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Author Topic: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME  (Read 35579 times)

AbruptSLR

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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #150 on: October 23, 2017, 09:45:18 PM »
Personally, I suspect that Sentinel-5P's instrument, Tropomi, will show that trends in the Arctic Stratospheric Ozone will lead to more frequent Super El Nino events; which may significantly increase the effective value of ECS later this century:

Title: "Can we solve the mysteries of Earth's atmosphere?"

http://www.euronews.com/2017/10/19/can-we-solve-the-mysteries-of-earth-s-atmosphere

Extract: "Several thousand weather balloons are launched worldwide every day, but it’s not enough to get a really global picture. To do that, you need to go to space, and that’s exactly what ESA’s Sentinel-5P satellite did on launch on 13th October this year.

It’s part of the European Commission’s Copernicus Earth observation programme, and will measure pollution and ozone levels in unprecedented detail, offering vital information on where harmful emission come from, and where they go.

“You have one satellite instrument measuring the complete globe,” stresses Pieternel Levelt, “It means that you have one calibrated instrument measuring everywhere – it means that you can compare the pollution levels in Europe directly with those in China and United States.”

Sentinel-5P’s instrument, Tropomi, developed in the Netherlands, could also be the instrument to clear up the mystery of whether our planet’s ozone layer is on the road to recovery, after harmful CFCs were banned in 1989."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #151 on: October 24, 2017, 03:37:08 PM »
It is important that CMIP6 models be properly calibrated to account for stratospheric water vapor and methane:

Noël, S., Weigel, K., Bramstedt, K., Rozanov, A., Weber, M., Bovensmann, H., and Burrows, J. P.: Water Vapour and Methane Coupling in the Stratosphere observed with SCIAMACHY Solar Occultation Measurements, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-893, in review, 2017.

https://www.atmos-chem-phys-discuss.net/acp-2017-893/

Abstract. An improved stratospheric water vapour data set has been derived from SCIAMACHY/ENVISAT solar occultation measurements.

It is based on the same algorithm which has already been successfully applied to methane and carbon dioxide retrievals, thus resulting in a consistent data set for theses three constituents covering the altitudes 17–45 km, the latitude range between about 50 and 70° N, and the time interval August 2002 to April 2012.

The new water vapour data agree with collocated results from ACE-FTS and MLS/Aura within about 5 %. A significant positive water vapour trend for the time 2003–2011 is observed at lower stratospheric altitudes of about 0.015 ppmv/year around 17 km. Between 30 and 37 km the trends become significantly negative (about −0.01 ppmv/year).

The combined analysis of the SCIAMACHY methane and water vapour time series reveals that stratospheric methane and water vapour are strongly correlated and show a clear temporal variation related to the Quasi-Biannual-Oscillation (QBO). Above about 20 km most of the water vapour seems to be produced by methane, but short-term fluctuations and a temporal variation on a scale of 5–6 years are observed.

At lower altitudes the balance between water vapour and methane is affected by stratospheric transport of water vapour and methane from the tropics to higher latitudes via the shallow branch of the Brewer-Dobson circulation and by the increasing methane input into the stratosphere due to the rise of tropospheric methane after 2007.
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #152 on: October 24, 2017, 03:57:01 PM »
Attribution is a big part of calibrating ESM projections:

Andrew D. King (23 October 2017), "Attributing changing rates of temperature record-breaking to anthropogenic influences", Earth's Future, DOI: 10.1002/2017EF000611

http://onlinelibrary.wiley.com/doi/10.1002/2017EF000611/abstract?utm_content=buffera7789&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Record-breaking temperatures attract attention from the media, so understanding how and why the rate of record-breaking is changing may be useful in communicating the effects of climate change. A simple methodology designed for estimating the anthropogenic influence on rates of record-breaking in a given timeseries is proposed here. The frequency of hot and cold record-breaking temperature occurrences is shown to be changing due to the anthropogenic influence on the climate. Using ensembles of model simulations with and without human-induced forcings, it is demonstrated that the effect of climate change on global record-breaking temperatures can be detected as far back as the 1930s. On local scales, a climate change signal is detected more recently at most locations. The anthropogenic influence on the increased occurrence of hot record-breaking temperatures is clearer than it is for the decreased occurrence of cold records. The approach proposed here could be applied in rapid attribution studies of record extremes to quantify the influence of climate change on the rate of record-breaking in addition to the climate anomaly being studied. This application is demonstrated for the global temperature record of 2016 and the Central England temperature record in 2014."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #153 on: October 26, 2017, 08:54:18 PM »
Climate scientists will need to re-calibrate their paleo climate models to account for the linked finding that paleo-ocean temperatures were cooler than previously assumed:

Bernard et. al. (2017), "Burial-induced oxygen-isotope re-equilibration of fossil foraminifera explains ocean paleotemperature paradoxes", Nature Communications, doi: 10.1038/s41467-017-01225-9

http://www.nature.com/articles/s41467-017-01225-9

See also:

Title: "Oceans Were Colder Than We Thought"

https://www.rdmag.com/news/2017/10/oceans-were-colder-we-thought

Extract: "A team of EPFL and European researchers has discovered a flaw in the way past ocean temperatures have been estimated up to now. Their findings could mean that the current period of climate change is unparalleled over the last 100 million years.

According to the methodology widely used by the scientific community, the temperature of the ocean depths 100 million years ago was around 15 degrees higher than current readings. This approach, however, is now being challenged: ocean temperatures may in fact have remained relatively stable throughout this period, which raises serious concerns about current levels of climate change. These are the conclusions of a study conducted by a team of French researchers from the French National Center for Scientific Research (CNRS), Sorbonne University and the University of Strasbourg, and Swiss researchers from the Swiss Federal Institute of Technology in Lausanne (EPFL) and the University of Lausanne. The study has just been published in Nature Communications.

“If we are right, our study challenges decades of paleoclimate research,” says Anders Meibom, the head of EPFL’s Laboratory for Biological Geochemistry and a professor at the University of Lausanne. Meibom is categorical: “Oceans cover 70% of our planet. They play a key role in the earth’s climate. Knowing the extent to which their temperatures have varied over geological time is crucial if we are to gain a fuller understanding of how they behave and to predict the consequences of current climate change more accurately.”"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #154 on: October 30, 2017, 10:58:30 PM »
The linked article and associated linked reference study MIS 19 (an interglacial period between 780 and 760 kya) that is particularly relevant to climate sensitivity during the Holocene and they find that the two warmest periods demonstrated particularly high climate sensitivities.  Hopefully, CMIP6 will calibrate their models accordingly:

Title: "Rapid climate changes across northern hemisphere in the earliest Middle Pleistocene"

https://phys.org/news/2017-09-rapid-climate-northern-hemisphere-earliest.html

Extract: "In the interglacial period between 780 and 760 thousand years ago, the Earth's orbital patterns were quite similar to the current (Holocene) era, so this interglacial climate could be useful in predicting the Earth's future climate.

This shows that the second half of this interglacial period, namely the earliest stage of the Middle Pleistocene, was a time of extreme climate change when ice sheets expanded and shrunk causing changes of several meters in sea levels, repeating every 500 to 2000 years.

The phenomenon of rapid temperature rises modulated by bi-centennial cycles ending with a sudden freeze only occurred during a very brief portion of this interglacial period, during the two warmest periods. There is a high possibility that this 200 year period marks the de Vries Cycle (205 years), when the climate was particularly sensitive to solar activity."

See also the associated reference at:

Masayuki Hyodo et al. Millennial-scale northern Hemisphere Atlantic-Pacific climate teleconnections in the earliest Middle Pleistocene, Scientific Reports (2017). DOI: 10.1038/s41598-017-10552-2

http://www.nature.com/articles/s41598-017-10552-2
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #155 on: November 07, 2017, 04:52:05 PM »
The linked reference indicates that resolution is a fundamental issue/problem for calibrating coupled climate-ice-sheet models to match the observed paleo-record.  This is not reassuring given that we may soon be moving into Super Interglacial conditions, which none of our current models can simulate.

Löfverström, M. and Liakka, J.: A note on the influence of atmospheric model resolution in coupled climate–ice-sheet simulations, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-235, in review, 2017.

https://www.the-cryosphere-discuss.net/tc-2017-235/

Abstract. Coupled climate–ice-sheet simulations have been growing in popularity in recent years. Experiments of this type are however challenging as ice sheets evolve over multi-millennial time scales, which is beyond the practical integration limit for most Earth-system models. A common method to increase model throughput is to trade resolution for computational efficiency (compromises accuracy for speed). Here, we analyze how the resolution of an atmospheric general circulation model (AGCM) influences the simulation quality of a standalone ice-sheet model. Four identical AGCM simulations of the Last Glacial Maximum (LGM) were run at different horizontal resolutions: T85 (1.4°), T42 (2.8°), T31 (3.8°), and T21 (5.6°). These simulations were subsequently used as forcing of an ice-sheet model. While the T85 climate forcing reproduces the LGM ice sheets to a high accuracy, the intermediate resolution cases (T42 and T31) fail to build the Eurasian Ice Sheet. The T21 case fails in both Eurasia and North America. Sensitivity experiments using different surface mass balance parameterizations improve the simulations of the Eurasian ice-sheet in the T42 case, but the compromise is a substantial ice buildup in Siberia. The T31 and T21 cases are not improving in the same way in Eurasia, though the latter simulates the continent-wide Laurentide Ice Sheet in North America. The difficulty to reproduce the LGM ice sheets in the T21 case is in broad agreement with previous studies using low-resolution atmospheric models, and is caused by a deterioration of the atmospheric climate between the T31 and T21 resolutions. It is speculated that this deficiency may demonstrate a fundamental problem using low-resolution atmospheric models in these types of experiments.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #156 on: November 10, 2017, 04:17:13 PM »
The linked reference indicates that in the pre-industrial era about two thirds of cloud condensation nuclei (CCN) came from biogenic vapors vs only about half today.  This means that clouds were different in the past compared with today, and that the nature tomorrow's clouds will depend on a combination of how much we clean-up anthropogenic aerosol emissions and also how well biogenic vapor sources fare (including deforestation impacts) in the future.  Climate models (e.g. CMIP6) should be calibrated with this information in mind:

Hamish Gordon, et al (24 August 2017), "Causes and importance of new particle formation in the present-day and preindustrial atmospheres" JGR Atmospheres, DOI: 10.1002/2017JD026844

http://onlinelibrary.wiley.com/doi/10.1002/2017JD026844/abstract

Abstract: "New particle formation has been estimated to produce around half of cloud-forming particles in the present-day atmosphere, via gas-to-particle conversion. Here we assess the importance of new particle formation (NPF) for both the present-day and the preindustrial atmospheres. We use a global aerosol model with parametrizations of NPF from previously published CLOUD chamber experiments involving sulfuric acid, ammonia, organic molecules, and ions. We find that NPF produces around 67% of cloud condensation nuclei at 0.2% supersaturation (CCN0.2%) at the level of low clouds in the preindustrial atmosphere (estimated uncertainty range 45–84%) and 54% in the present day (estimated uncertainty range 38–66%). Concerning causes, we find that the importance of biogenic volatile organic compounds (BVOCs) in NPF and CCN formation is greater than previously thought. Removing BVOCs and hence all secondary organic aerosol from our model reduces low-cloud-level CCN concentrations at 0.2% supersaturation by 26% in the present-day atmosphere and 41% in the preindustrial. Around three quarters of this reduction is due to the tiny fraction of the oxidation products of BVOCs that have sufficiently low volatility to be involved in NPF and early growth. Furthermore, we estimate that 40% of preindustrial CCN0.2% are formed via ion-induced NPF, compared with 27% in the present day, although we caution that the ion-induced fraction of NPF involving BVOCs is poorly measured at present. Our model suggests that the effect of changes in cosmic ray intensity on CCN is small and unlikely to be comparable to the effect of large variations in natural primary aerosol emissions."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #157 on: November 10, 2017, 05:19:54 PM »
The linked reference studies the paleo decay of the Cordilleran ice sheet and finds that it lost most of its ice mass earlier than consensus science previously thought, and it lost much of its ice mass over a relatively short period.  CMIP6 models should be calibrated with such information which indicates that dry land ice sheets may be less stable during global warming periods.  Personally, I am concerned about the impact of rainfall at increasingly high latitudes (with warming) on both the Greenland Ice Sheet, on Arctic permafrost, and on the WAIS:

B. Menounos et al (10 Nov 2017), "Cordilleran Ice Sheet mass loss preceded climate reversals near the Pleistocene Termination", Science, Vol. 358, Issue 6364, pp. 781-784, DOI: 10.1126/science.aan3001

http://science.sciencemag.org/content/358/6364/781

Abstract: "The Cordilleran Ice Sheet (CIS) once covered an area comparable to that of Greenland. Previous geologic evidence and numerical models indicate that the ice sheet covered much of westernmost Canada as late as 12.5 thousand years ago (ka). New data indicate that substantial areas throughout westernmost Canada were ice free prior to 12.5 ka and some as early as 14.0 ka, with implications for climate dynamics and the timing of meltwater discharge to the Pacific and Arctic oceans. Early Bølling-Allerød warmth halved the mass of the CIS in as little as 500 years, causing 2.5 to 3.0 meters of sea-level rise. Dozens of cirque and valley glaciers, along with the southern margin of the CIS, advanced into recently deglaciated regions during the Bølling-Allerød and Younger Dryas."

Disappearance of an ice sheet

The Cordilleran Ice Sheet is thought to have covered westernmost Canada until about 13,000 years ago, even though the warming and sea level rise of the last deglaciation had begun more than a thousand years earlier. This out-of-phase behavior has puzzled glaciologists because it is not clear what mechanisms could account for it. Menounos et al. report measurements of the ages of cirque and valley glaciers that show that much of western Canada was ice-free as early as 14,000 years ago—a finding that better agrees with the record of global ice volume (see the Perspective by Marcott and Shakun). Previous reconstructions seem not to have adequately reflected the complexity of ice sheet decay.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #158 on: November 11, 2017, 11:19:29 PM »
Calibrating CMIP6 models to lessons learned from the last glacial maximum is a good idea:

Kageyam et al. (2017), "The PMIP4 contribution to CMIP6–Part4: Scientific objectives and experimental design of the PMIP4-CMIP6 Last Glacial Maximum experiments and PMIP4 sensitivity experiments", Geosci. Model Dev., 10, 4035–4055, https://doi.org/10.5194/gmd-10-4035-2017

https://www.geosci-model-dev.net/10/4035/2017/gmd-10-4035-2017-relations.html
&
https://www.geosci-model-dev.net/10/4035/2017/gmd-10-4035-2017.pdf

Abstract: "Abstract. The Last Glacial Maximum (LGM, 21000 years ago) is one of the suite of paleoclimate simulations included in the current phase of the Coupled Model Intercomparison Project (CMIP6). It is an interval when insolation was similar to the present, but global ice volume was at a maximum, eustatic sea level was at or close to a minimum, green house gas concentrations were lower, atmospheric aerosol loadings were higher than today, and vegetation and land surface characteristics were different from today. The LGM has been a focus for the Paleoclimate Modelling Intercomparison Project (PMIP) since its inception, and thus many of the problems that might be associated with simulating such a radically different climate are well documented. The LGM state provides an ideal case study for evaluating climate model performance because the changes in forcing and temperature between the LGM and pre-industrial are of the same order of magnitude as those projected for the end of the 21st century. Thus, the CMIP6 LGM experiment could provide additional information that can be used to constrain estimates of climate sensitivity. The design of the Tier 1 LGM experiment (lgm) includes an assessment of uncertainties in boundary conditions, in particular through the use of different reconstructions of the ice sheets and of the change in dust forcing. Additional (Tier 2) sensitivity experiments have been designed to quantify feedbacks associated with land surface changes and aerosol loadings, and to isolate the role of individual forcings. Model analysis and evaluation will capitalize on the relative abundance of paleoenvironmental observations and quantitative climate reconstructions already available for the LGM."

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #159 on: November 14, 2017, 12:37:02 AM »
The linked reference discusses the study of microbial assemblages in the paleoceanographic record to better understand the sulfate-methane transition zone.  Such information could better delineate risks of future methane releases from Arctic marine sediments:

Han et al. (2017), "Inference on Paleoclimate Change Using Microbial Habitat Preference in Arctic Holocene Sediment", Scientific Reports 7, Article #9652, doi: 10.1038/s41598-017-08757-6

https://www.nature.com/articles/s41598-017-08757-6
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #160 on: November 25, 2017, 04:37:28 PM »
Calibrating CMIP6 models to lessons learned from 850 to 1849, and from 1850 to 2014, is a good idea

Jungclaus, J. H., Bard, E., Baroni, M., Braconnot, P., Cao, J., Chini, L. P., Egorova, T., Evans, M., González-Rouco, J. F., Goosse, H., Hurtt, G. C., Joos, F., Kaplan, J. O., Khodri, M., Klein Goldewijk, K., Krivova, N., LeGrande, A. N., Lorenz, S. J., Luterbacher, J., Man, W., Maycock, A. C., Meinshausen, M., Moberg, A., Muscheler, R., Nehrbass-Ahles, C., Otto-Bliesner, B. I., Phipps, S. J., Pongratz, J., Rozanov, E., Schmidt, G. A., Schmidt, H., Schmutz, W., Schurer, A., Shapiro, A. I., Sigl, M., Smerdon, J. E., Solanki, S. K., Timmreck, C., Toohey, M., Usoskin, I. G., Wagner, S., Wu, C.-J., Yeo, K. L., Zanchettin, D., Zhang, Q., and Zorita, E.: The PMIP4 contribution to CMIP6 – Part 3: The last millennium, scientific objective, and experimental design for the PMIP4 past1000 simulations, Geosci. Model Dev., 10, 4005-4033, https://doi.org/10.5194/gmd-10-4005-2017, 2017

https://www.geosci-model-dev.net/10/4005/2017/

Abstract. The pre-industrial millennium is among the periods selected by the Paleoclimate Model Intercomparison Project (PMIP) for experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the PMIP (PMIP4). The past1000 transient simulations serve to investigate the response to (mainly) natural forcing under background conditions not too different from today, and to discriminate between forced and internally generated variability on interannual to centennial timescales. This paper describes the motivation and the experimental set-ups for the PMIP4-CMIP6 past1000 simulations, and discusses the forcing agents orbital, solar, volcanic, and land use/land cover changes, and variations in greenhouse gas concentrations. The past1000 simulations covering the pre-industrial millennium from 850 Common Era (CE) to 1849 CE have to be complemented by historical simulations (1850 to 2014 CE) following the CMIP6 protocol. The external forcings for the past1000 experiments have been adapted to provide a seamless transition across these time periods. Protocols for the past1000 simulations have been divided into three tiers. A default forcing data set has been defined for the Tier 1 (the CMIP6 past1000) experiment. However, the PMIP community has maintained the flexibility to conduct coordinated sensitivity experiments to explore uncertainty in forcing reconstructions as well as parameter uncertainty in dedicated Tier 2 simulations. Additional experiments (Tier 3) are defined to foster collaborative model experiments focusing on the early instrumental period and to extend the temporal range and the scope of the simulations. This paper outlines current and future research foci and common analyses for collaborative work between the PMIP and the observational communities (reconstructions, instrumental data).
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #161 on: December 01, 2017, 05:31:42 PM »
The linked article and subsequent associated linked references, address efforts to improve/advance climate forecasting.  While the article addresses a range of efforts from correcting model bias to predicting snow (& associated albedo effects) distribution, in this post I only extract sections related to efforts to better understand the telecommunication of tropical heat energy to the Arctic (see the attached image & caption, which does not show telecommunications of tropical heat energy to Antarctica, which also occurs).  While climate modelers are working hard to improve their projections, I noted that none of the efforts discussed consider the impacts of freshwater hosing events (such as the possible collapse of the WAIS this century).

Merryfield, W. J., F. J. Doblas-Reyes, L. Ferranti, J.-H. Jeong, Y. J. Orsolini, R. I. Saurral, A. A. Scaife, M. A. Tolstykh, and M. Rixen (2017), Advancing climate forecasting, Eos, 98, https://doi.org/10.1029/2017EO086891

https://eos.org/project-updates/advancing-climate-forecasting?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz120117

Extract: "The heaviest rainfall on Earth occurs over tropical oceans. As water vapor condenses to form droplets in the moist tropical air, the water releases substantial amounts of latent heat. This heat produces deep convection currents that propel the resulting clouds to great heights. The accompanying uplift turns into divergent horizontal winds near the tops of these clouds, high in the troposphere.

Variations in climate alter the patterns of tropical rainfall from year to year. Shifts in upper level divergent winds drive disturbances in atmospheric circulation. These disturbances, known as Rossby or planetary waves, propagate eastward and poleward away from the equator in the winter hemisphere and affect atmospheric circulation in the extratropical regions, outside of the tropics. Such tropical influences on extratropical climate are known as teleconnections (Figure 1).

In some regions of the tropics, climate variations are relatively predictable because strong couplings between the tropical ocean and atmosphere modulate climate on relatively slow oceanic timescales. The most prominent such modulation is the El Niño–Southern Oscillation.
Because the predictable tropical climate influences the less predictable extratropical climate through teleconnections, tropical predictability could enable skillful predictions of the extratropical climate.

These interconnections raise several important and related questions:
•   How much do tropical teleconnections contribute to extratropical climate variability?
•   How well are extratropical circulation responses to tropical climate variability represented in current climate models?
•   To what extent can improvements in the modeling of teleconnections improve the skill of extratropical climate forecasts?

To address these questions, the WGSIP teleconnection initiative is examining how well climate forecast models represent the chain of causation connecting variations in tropical rainfall to planetary wave forcing and propagation and hence to modulation of extratropical climate. A pilot analysis of one model [Scaife et al., 2017] is being extended to many models, drawing on the CHFP archive and other hindcast data sources.

Recent results [Molteni et al., 2015] indicate that teleconnections are more directly connected to tropical rainfall than sea surface temperature, which has often been used to infer teleconnection driving. In addition, climate forecast models show encouraging levels of skill at predicting seasonal rainfall in all tropical ocean basins during the Northern Hemisphere’s winter months, especially in the eastern and western Pacific.

Ongoing efforts will determine how well different models represent the sources and propagation of planetary waves driven by tropical rainfall. We will then relate those model attributes to skill in forecasting winter climate variations in the northern extratropics, including the Arctic and North Atlantic oscillations."

Caption: "Fig. 1. Averaged atmospheric response during winter in the Northern Hemisphere to recent El Niño events, connecting atmospheric changes in the tropics with those at latitudes farther north and south. Dots represent approximate pathways of planetary waves [after Scaife et al., 2017]. Colors show associated changes in sea level pressure (SLP) in hectopascals (hPa), indicative of atmospheric circulation changes. In the Northern Hemisphere, changes are clockwise for positive contours, represented by warm colors, and counterclockwise for negative contours, represented by cool colors; these directions are opposite in the Southern Hemisphere. Credit: Adam Scaife"

See also:
Scaife, A. A., et al. (2017), Tropical rainfall, Rossby waves and regional winter climate predictions, Q. J. R. Meteorol. Soc., 143, 1–11, https://doi.org/10.1002/qj.2910.

http://onlinelibrary.wiley.com/doi/10.1002/qj.2910/abstract?systemMessage=Wiley+Online+Library+will+be+unavailable+on+2nd+Dec+2017+starting+from+0800+EST+%2F+1300+GMT+%2F+21.00+SGT+for+2.5+hours+due+to+urgent+server+maintenance.+Apologies+for+the+inconvenience.

Abstract: "Skilful climate predictions of the winter North Atlantic Oscillation and Arctic Oscillation out to a few months ahead have recently been demonstrated, but the source of this predictability remains largely unknown. Here we investigate the role of the Tropics in this predictability. We show high levels of skill in tropical rainfall predictions, particularly over the Pacific but also the Indian and Atlantic Ocean basins. Rainfall fluctuations in these regions are associated with clear signatures in tropical and extratropical atmospheric circulation that are approximately symmetric about the Equator in boreal winter. We show how these patterns can be explained as steady poleward propagating linear Rossby waves emanating from just a few key source regions. These wave source ‘hotspots’ become more or less active as tropical rainfall varies from winter to winter but they do not change position. Finally, we show that predicted tropical rainfall explains a highly significant fraction of the predicted year-to-year variation of the winter North Atlantic Oscillation."
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Tompkins, A. M., et al. (2017), The Climate-system Historical Forecast Project: Providing open access to seasonal forecast ensembles from centers around the globe, Bull. Am. Meteorol. Soc., https://doi.org/10.1175/BAMS-D-16-0209.1.

http://journals.ametsoc.org/doi/10.1175/BAMS-D-16-0209.1

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Sanchez-Gomez, E., et al. (2016), Drift dynamics in a coupled model initialized for decadal forecasts, Clim. Dyn., 46, 1819–1840, https://doi.org/10.1007/s00382-015-2678-y.

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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #162 on: December 01, 2017, 05:42:39 PM »
The linked reference indicates that current models of methane emissions from peatlands need to be improved to account for hotspots in the peat/soil with varying conditions (including varying ground water elevation):

Yang et al. (2017), "Evaluating the Classical Versus an Emerging Conceptual Model of Peatland Methane Dynamics", Global Biogeochemical Cycles, doi: 10.1002/2017GB005622

http://onlinelibrary.wiley.com/doi/10.1002/2017GB005622/abstract;jsessionid=120CA9C25B38DF660F8C127A470C3997.f02t01?systemMessage=Wiley+Online+Library+will+be+unavailable+on+2nd+Dec+2017+starting+from+0800+EST+%2F+1300+GMT+%2F+21.00+SGT+for+2.5+hours+due+to+urgent+server+maintenance.+Apologies+for+the+inconvenience.

See also:

Thompson, E. (2017), A new model yields a better picture of methane fluxes, Eos, 98, https://doi.org/10.1029/2017EO086831

https://eos.org/research-spotlights/a-new-model-yields-a-better-picture-of-methane-fluxes?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz120117

Extract: "… generally speaking, methane is produced below the water table, where there is little to no oxygen, and it is destroyed above the water table, especially right at the boundary, where the most methane accumulates. When the water table is high, a greater proportion of the soil falls into methane-producing conditions. Likewise, when the water table drops, more soil is exposed to oxygen and thereby able to destroy methane. Current models commonly use this relationship to predict net methane production essentially on the basis of water table height.

Now Yang et al. suggest updating this classical conceptual model to include new information on methane dynamics gleaned from recent studies: For example, oxygen-poor pockets within the soil produce methane even above the water table, and methane can be destroyed below the water table in the absence of oxygen, depending on the presence of specific microbes and molecules in the soil that can play the role of oxygen to gain the electrons lost by methane."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on ACME
« Reply #163 on: December 02, 2017, 11:03:20 PM »
The first linked pdf provides a useful summary of the new, DOE sponsored, Energy Exascale Earth System Model, E3SM, project strategy (see also the related attached images), that is subsuming the Accelerated Climate Model for Energy, ACME, project.  The E3SM project was developed, and scheduled to run through 2027, largely because it was concluded that the ACME project could not meet the goal of adequately modeling Earth Systems focused on Water Cycles, Biogeochemistry and Cryosphere Systems; which also implies that E3SM management has concluded that the CMIP6 models are also inadequate to answer associated questions associated with climate risk.  Furthermore, in the extract below, I focus a little bit extra on Cryosphere Systems and I conclude that even after the E3SM project concludes in 2027 that it will not likely be able to replicate the findings of DeConto & Pollard (2016-extended); which may not be the objective of this effort which seem better organized to address the risks of Hansen's ice-climate feedback mechanism [as one can always accept the findings of ice cliff and hydrofracturing models and then introduce the required hosing into any model and Hansen et al (2016) did].

While this E3SM project is impressive and clearly engages the thinking of serious scientists; nevertheless, the final E3SM model is left under the control of Oak Ridge National Laboratory, whom I personally do not trust with regard to their geoengineering efforts (i.e. geoengineering can easily be weaponized which is one of ORNL's specialties).  Indeed, after reviewing the write-up in the various linked sources, I am left with the distinct impression that the authors consider the collapse of the WAIS this century as a foregone conclusion and they just want a model powerful enough to guide geoengineering efforts beginning between 2040 and 2050.  I hope that I am wrong, but I am concerned that what they learned in Phase 1 of the ACME program concerned them [with regard to such topics as: ECS, ESS, GWP25-100 of methane, Ozone RF, Biogeochemistry, Bipolar Seesaw/Climate Attractors, Polar Amplification (telecommunication with the tropics, future rainfall at the poles and albedo flip), and Ice-Climate Feedback] enough to fund and organize the much larger E3SM project. 

D. Bader (September 20, 2017), "Energy Exascale Earth System Model (E3SM) Project Strategy"

https://e-reports-ext.llnl.gov/pdf/892182.pdf

Extract: "Mission and science needs defined our three grand challenge science questions and the simulations envisioned to answer those questions by 2027. The grand challenge simulations are not yet possible with current model and computing capabilities. Nevertheless, we developed a set of achievable experiments that make major advances toward answering the grand challenge questions using a modeling system, v1, which we have constructed to run on leadership computing architectures available to the project now. Like all research projects, our early results will be used to refine science questions and develop new testable hypotheses to be addressed with subsequent versions of the modeling system. As shown on the left side of Figure 1, E3SM envisions simulation campaigns of four to five years each with successive versions of the modeling system. Every campaign will inform the next, and we envision three campaigns with successive versions of the modeling system leading to the grand challenge simulations in approximately 10 years.

The three drivers (and each driver’s summary term used hereafter) are:

1. (Water Cycle) How do the hydrological cycle and water resources interact with the climate system on local to global scales?

2. (Biogeochemistry) How do biogeochemical cycles interact with global climate change?

3. Cryosphere Systems) How do rapid changes in cryospheric systems interact with the climate system?

The E3SM project will target at least two base model configurations. The first configuration is a low resolution coupled model with horizontal resolutions comparable to climate models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6). This version will provide more rapid turnaround for development purposes. It will also serve as a useful benchmark for comparison with other CMIP-class models and as the control for evaluating the impacts of increasing resolution. This low resolution coupled model configuration will also be used for the v1 biogeochemistry cycle experiments with the goal of gaining experience with simulations that include biogeochemical processes in the atmosphere, land, ocean, and sea ice components. The second configuration is a global coupled high-resolution version that can provide sufficient detail to address science questions and can further provide improved decision-relevant simulation results for DOE mission needs. This configuration will serve to produce benchmark simulations to evaluate model scientific and computational performance. Simulations for the water cycle experiments will utilize both the low and high resolution configurations to evaluate the impacts of model resolution. Additional configuration will feature regional refinement over North America for better representation of physical and dynamical processes and regional refinement for the ocean and ice over Antarctica and the Southern Ocean to simulate the interactions between ocean circulation and ice shelf cavities.

The ice sheet component, MPAS-LI, will span the Antarctic continent using variable-resolution (down to ~500 m) in regions of dynamic complexity, such as ice streams and grounding lines, but the model is static for the v1 cryosphere experiments. This v1 global uniform high-resolution coupled configuration will be used in the water cycle experiments."

See also:

(http://science.energy.gov/ascr/research/scidac/co-design/)
&
https://exascaleproject.org/wp-content/uploads/2017/04/Messina-ECP-Presentation-HPCUser-
Forum-2017-04-18.pdf
&
https://www.wcrp-climate.org/images/modelling/WGCM/WGCM21/10oct/11_10-Meehl_CESM_WGCM_2017.pdf
&
https://www2.cisl.ucar.edu/sites/default/files/iCAS%202017%20Messina%20keynote.final_.pdf

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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #164 on: December 04, 2017, 03:12:21 AM »
The linked reference is proposing to develop 'climate response functions', CRFs, to abrupt stepwise changes in forcing fields.  I highly support implementation of this dynamical approach to improving models for the Arctic Ocean.

Marshall, J., Scott, J., and Proshutinsky, A.: “Climate response functions” for the Arctic Ocean: a proposed coordinated modelling experiment, Geosci. Model Dev., 10, 2833-2848, https://doi.org/10.5194/gmd-10-2833-2017, 2017.

https://www.geosci-model-dev.net/10/2833/2017/

Abstract. A coordinated set of Arctic modelling experiments, which explore how the Arctic responds to changes in external forcing, is proposed. Our goal is to compute and compare climate response functions (CRFs) – the transient response of key observable indicators such as sea-ice extent, freshwater content of the Beaufort Gyre, etc. – to abrupt step changes in forcing fields across a number of Arctic models. Changes in wind, freshwater sources, and inflows to the Arctic basin are considered. Convolutions of known or postulated time series of these forcing fields with their respective CRFs then yield the (linear) response of these observables. This allows the project to inform, and interface directly with, Arctic observations and observers and the climate change community. Here we outline the rationale behind such experiments and illustrate our approach in the context of a coarse-resolution model of the Arctic based on the MITgcm. We conclude by summarizing the expected benefits of such an activity and encourage other modelling groups to compute CRFs with their own models so that we might begin to document their robustness to model formulation, resolution, and parameterization.


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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #165 on: December 08, 2017, 04:03:09 PM »
The linked information is valuable for helping to calibrate ESMs:

Title: "Examining our Eyes in the Sky"

https://eos.org/editors-vox/examining-our-eyes-in-the-sky?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz120817

Extract: "A recent paper in Reviews of Geophysics explored the challenges of validating data collected from Earth observation satellites."

See also:

Loew, A., et al. (2017), Validation practices for satellite-based Earth observation data across communities, Rev. Geophys., 55, 779–817, doi:10.1002/2017RG000562.

http://onlinelibrary.wiley.com/doi/10.1002/2017RG000562/epdf
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #166 on: December 15, 2017, 04:39:40 PM »
It looks like the Trump Administration is determined to hobble the DOE previous efforts to better calibrate state-of-the-art ESMs:

Popkin, G. (2017), Major federal tropical research project to cease 7 years early, Eos, 98, https://doi.org/10.1029/2017EO088505. Published on 11 December 2017.

https://eos.org/articles/major-federal-tropical-research-project-to-cease-7-years-early?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz121517

Extract: "When the U.S. Department of Energy’s (DOE) $100 million Next-Generation Ecosystem Experiment–Tropics (NGEE-Tropics) launched in 2015, Ariel Lugo, an ecologist and director of the International Institute of Tropical Forestry (IITF) in Río Piedras, Puerto Rico, was excited.  He felt that the project’s large budget and international scope might help it take on one of the field’s long-standing challenges: helping computer models accurately represent how tropical forests will respond to climate change.

The plan was for it to run until 2025. But this spring, sometime after the release of the White House’s 2018 budget request in May, the NGEE-Tropics project’s leaders began telling collaborators the project would shut down in 2018. The project is slated to end 7 years ahead of schedule.

But the massive computer simulations that scientists build to forecast Earth’s future make inconsistent predictions about whether tropical forests will absorb or release carbon in the future. “Almost any global model, no matter what you’re modeling, whether it be carbon dioxide, whether it be temperature changes—the predictions that are made, they always diverge in tropics,” Lugo said.

The outcomes depend on assumptions about how trees and soil microbes will respond to higher temperatures, higher carbon dioxide levels, changes in rainfall and nutrient levels, and other factors. To improve how models represent these processes, Lugo and other project scientists have designed studies to tease out data on how factors such as soil nutrients, water movement, and root decomposition influence forest growth and carbon release."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #167 on: December 15, 2017, 05:35:06 PM »
The linked open access reference indicates that land use change will likely play a 50% larger role in future radiative forcing scenarios than previously assumed by the SSP scenarios:

Fuchs, R., Prestele, R., and Verburg, P. H.: A global assessment of gross and net land change dynamics for current conditions and future scenarios, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2017-121, in review, 2017.

https://www.earth-syst-dynam-discuss.net/esd-2017-121/
&
https://www.earth-syst-dynam-discuss.net/esd-2017-121/esd-2017-121.pdf

Abstract. The consideration of gross land changes, meaning all area gains and losses within a pixel or administrative unit (e.g. country), plays an essential role in the estimation of total land changes. Gross land changes affect the magnitude of total land changes, which feeds back to the attribution of biogeochemical and biophysical processes related to climate change in Earth System Models. Global empirical studies on gross land changes are currently lacking. Whilst the relevance of gross changes for global change has been indicated in the literature, it is not accounted for in future land change scenarios. In this study, we extract gross and net land change dynamics from large-scale and high-resolution (30–100 m) remote sensing products to create a new global gross and net change dataset. Subsequently, we developed an approach to integrate our empirically derived gross and net changes with the results of future simulation models, by accounting for the gross and net change addressed by the land use model and the gross and net change that is below the resolution of modelling. Based on our empirical data, we found that gross land change within 0.5-degree grid cells were substantially larger than net changes in all parts of the world. As 0.5-degree grid cells are a standard resolution of Earth System Models, this leads to an underestimation of the amount of change. This finding contradicts earlier studies, which assumed gross land changes to appear in shifting cultivation areas only. Applied in a future scenario, the consideration of gross land changes led to approximately 50 % more land changes globally compared to a net land change representation. Gross land changes were most important in heterogeneous land systems with multiple land uses (e.g. shifting cultivation, smallholder farming, and agro-forestry systems). Moreover, the importance of gross changes decreased over time due to further polarization and intensification of land use. Our results serve as empirical database for land change dynamics that can be applied in Earth System Models and Integrated Assessment Models.


Extract: "In this study, we could show that that, based on empirical data, gross land changes occur globally in every world region. This finding contradicts earlier studies, which assumed gross land changes to appear in shifting cultivation areas only. Applied to our future reference scenario, net land changes led globally to an average of 0.92% area change per year, while for gross land changes the average change rate was 1.35% per year. This is an increase of roughly 50% compared to the net change approach.  Empirical data contributed ca. 80% of changes in the future scenario we used. This highlights the importance of accounting for sub-pixel processes in global assessments. In our scenario, gross land changes appeared in regional patterns, most dominant in Eastern Europe, Turkey, the Sahel zone, the United States and development countries in transition, like the BRICS states (Brazil, Russia, India, China and South Africa). Large-scale and high-resolution remote sensing data was crucial for this kind of assessment. This highlights the increasing importance of land related remote sensing data in global assessments. With our approach, it is possible to further decrease uncertainties in land changes dynamics and related land atmosphere fluxes in ESMs.  This again, helps to improve accuracies for future mitigation and adaptation scenarios."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #168 on: December 19, 2017, 03:40:36 PM »
The findings of the linked research on the impact of cosmic rays on cloud formation may help to calibrate climate models using paleo data:

Title: "The missing link between exploding stars, clouds, and climate on Earth"

https://phys.org/news/2017-12-link-stars-clouds-climate-earth.html

Extract: "The study reveals that atmospheric ions, produced by energetic cosmic rays raining down through the atmosphere, help the growth and formation of cloud condensation nuclei—the seeds necessary for forming clouds in the atmosphere.

When the ionization in the atmosphere changes, the number of cloud condensation nuclei changes, affecting the properties of clouds. More cloud condensation nuclei mean more clouds and a colder climate, and vice versa. Since clouds are essential for the amount of solar energy reaching the surface of Earth, the implications are significant for the understanding of past climate variation and also for future climate changes."

See also:

H. Svensmark et al, Increased ionization supports growth of aerosols into cloud condensation nuclei, Nature Communications (2017). DOI: 10.1038/s41467-017-02082-2

http://www.nature.com/articles/s41467-017-02082-2

Edit: I note that the cited research may be of little practical value as the impacts are primarily of interest during Supernovae events; which are short-term in nature and difficult to predict (for either forecasts or hindcasts)
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #169 on: December 27, 2017, 03:00:17 AM »
I do not have time to address the many important topics discussed in the open access linked reference, but it is well worth a look:

Eds: Crucifix M, de vernal A, Franzke C & von Gunten L (2017), "Centennial to Millennial Climate Variability", Past Global Changes Magazine, vol. 25(3), 131-166,

http://pastglobalchanges.org/products/pages-magazine/11504

Edit:
Extract from Crucifix et al 2017, https://doi.org/10.22498/pages.25.3.133: "Arguably, centennial variability has been the forgotten orphan of climate dynamics theory. In a 1990 paper titled "Three basic problems of palaeoclimate modelling", the late Barry Saltzman presented the centennial timescale as a zone with a variability gap – a demilitarized zone, separating people interested in weather from those interested in the slow evolution of climate.

Saltzman was putting forward an idea that has, until recently, deeply penetrated our paradigms of climate modeling. General circulation models generate weather. A so-called "climate snapshot" is often an average of the generated weather over a few centuries or so. At the other extreme, the dynamics of ice ages are simulated with models which do not include weather variability. We know today that this separation is no longer tenable. There is centennial variability, which seamlessly connects weather to the great ice ages.

Caption for the attached image from Kopp et al 2017, https://doi.org/10.22498/pages.25.3.148: "Figure 1: Sea-level reconstructions proposed for the Last Interglacial period (not to precise scale). Different interpretations have been made regarding the number of sea-level peaks, though several suggest evidence for one or multiple sea-level oscillations on millennial timescales.
« Last Edit: December 27, 2017, 01:37:33 PM by AbruptSLR »
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #170 on: January 03, 2018, 04:46:27 PM »
The research cited in the linked article implies that if the area burned by wildfires increase with continued global warming then net methane emission should also increase:

Title: "NASA-led study solves a methane puzzle"
https://phys.org/news/2018-01-nasa-led-methane-puzzle.html

Extract: "Methane emissions have been rising sharply since 2006. Different research teams have produced viable estimates for two known sources of the increase: emissions from the oil and gas industry, and microbial production in wet tropical environments like marshes and rice paddies. But when these estimates were added to estimates of other sources, the sum was considerably more than the observed increase. In fact, each new estimate was large enough to explain the whole increase by itself.

Scientist John Worden of NASA's Jet Propulsion Laboratory in Pasadena, California, and colleagues focused on fires because they're also changing globally. The area burned each year decreased about 12 percent between the early 2000s and the more recent period of 2007 to 2014, according to a new study using observations by NASA's Moderate Resolution Imaging Spectrometer satellite instrument. The logical assumption would be that methane emissions from fires have decreased by about the same percentage. Using satellite measurements of methane and carbon monoxide, Worden's team found the real decrease in methane emissions was almost twice as much as that assumption would suggest.

When the research team subtracted this large decrease from the sum of all emissions, the methane budget balanced correctly, with room for both fossil fuel and wetland increases."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #171 on: January 03, 2018, 05:11:13 PM »
It will be interesting to see how much precipitation variability impacts tree cover in the tropics:

Xiangtao Xu et al. (2 January 2018), "Tree cover shows strong sensitivity to precipitation variability across the global tropics", Global Ecology and Biogeography, DOI: 10.1111/geb.12707

http://onlinelibrary.wiley.com/doi/10.1111/geb.12707/abstract?utm_content=bufferfa373&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #172 on: January 03, 2018, 05:13:43 PM »
Per the linked article if we keep following RCP 8.5 (assuming ECS = 3.1C), then about 25% of the Earth will be subject to desertification by 2050 (see the attached image).  It will be interesting to see if this reduces the land based carbon sink in these impacted areas:

Chang-Eui Park et al (2018), "Keeping global warming within 1.5 °C constrains emergence of aridification",  Nature Climate Change, doi:10.1038/s41558-017-0034-4

http://www.nature.com/articles/s41558-017-0034-4
&
http://www.nature.com/articles/s41558-017-0034-4.epdf?referrer_access_token=uomV724E6L7Azgr_quk6KdRgN0jAjWel9jnR3ZoTv0Md-_o5A1rhm4JzTytmIvTkmxaaT7siHGll-VC_gYGc86rzaCGyHAOR4rvUdRgQU-l25yhfdvQ3YA9Sav1Hp-9FF5MB-iTHjnQ37ZcRAyET_8yswPHc50VudILwTqUqzbfytP20P8axT5rTSHLyrhghYS-UOsW-GxJvHJaa_8Fq3dvxpyfvvNDVuVY3ll6olzw%3D&tracking_referrer=www.newsweek.com

Abstract: "Aridity—the ratio of atmospheric water supply (precipitation; P) to demand (potential evapotranspiration; PET)—is projected to decrease (that is, areas will become drier) as a consequence of anthropogenic climate change, exacerbating land degradation and desertification. However, the timing of significant aridification relative to natural variability—defined here as the time of emergence for aridification (ToEA)—is unknown, despite its importance in designing and implementing mitigation policies. Here we estimate ToEA from projections of 27 global climate models (GCMs) under representative concentration pathways (RCPs) RCP4.5 and RCP8.5, and in doing so, identify where emergence occurs before global mean warming reaches 1.5 °C and 2 °C above the pre-industrial level. On the basis of the ensemble median ToEA for each grid cell, aridification emerges over 32% (RCP4.5) and 24% (RCP8.5) of the total land surface before the ensemble median of global mean temperature change reaches 2 °C in each scenario. Moreover, ToEA is avoided in about two-thirds of the above regions if the maximum global warming level is limited to 1.5 °C. Early action for accomplishing the 1.5 °C temperature goal can therefore markedly reduce the likelihood that large regions will face substantial aridification and related impacts."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #173 on: January 16, 2018, 01:46:59 AM »
The linked reference provides calibration information about the influence vegetation on the stability on the southern edge of Arctic permafrost regions:

Weichao Guo et al (15 April 2018), "Vegetation can strongly regulate permafrost degradation at its southern edge through changing surface freeze-thaw processes", Agricultural and Forest Meteorology
Volume 252, Pages 10–17, https://doi.org/10.1016/j.agrformet.2018.01.010

http://www.sciencedirect.com/science/article/pii/S0168192318300108

Abstract: "Permafrost contains twice as much carbon as the atmosphere and the degradation of permafrost due to climatic warming, which could potentially change the global carbon cycle and could also enhance global climate change. It is well studied that permafrost degradation could result in vegetation transition. Aboveground vegetation can act as a buffer for climatic warming, however its role in regulating permafrost degradation remains unclear. In this study we examined how different vegetation types regulated the amplitude and duration of diurnal soil freeze/thaw (FT) cycles and the timing of seasonal soil FT. Soil temperature data (hourly and half hourly) was collected from paired forest-steppe sampling plots spanning a large spatial gradient from northern China to southern Siberia, Russia from 2008 to 2015. FT cycles were found to be larger in amplitude and longer in duration in steppe sites in comparison to forest sites. Soils in the forest sites and steppe sites freeze almost simultaneously, but experience a delay in thawing of approximately 14, 19 and 25 days for deciduous broadleaf forest, evergreen coniferous forest, and deciduous coniferous forest, respectively. Variations in snow accumulation due to differences in vegetation structure as opposed to solar radiation were responsible for the disparity in thaw timing. These findings imply that deciduous conifer forest in east Eurasia could reduce carbon emissions more effectively than evergreen conifer forest in west Eurasia by slowing down warming-induced permafrost degradation during spring thaw."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #174 on: January 23, 2018, 06:51:31 PM »
The linked reference confirms at most climate simulations do not capture the greater polar amplification during the Eocene.  As CO2e approaches 560ppm this type of information could become highly relevant to modern times:

David Evans, et al (January 22, 2018), "Eocene greenhouse climate revealed by coupled clumped isotope-Mg/Ca thermometry", PNAS, doi: 10.1073/pnas.1714744115

http://www.pnas.org/content/early/2018/01/12/1714744115.abstract

Significance: "Reconstructing the degree of warming during geological periods of elevated CO2 provides a way of testing our understanding of the Earth system and the accuracy of climate models. We present accurate estimates of tropical sea-surface temperatures (SST) and seawater chemistry during the Eocene (56–34 Ma before present, CO2 >560 ppm). This latter dataset enables us to reinterpret a large amount of existing proxy data. We find that tropical SST are characterized by a modest warming in response to CO2. Coupling these data to a conservative estimate of high-latitude warming demonstrates that most climate simulations do not capture the degree of Eocene polar amplification."

Abstract: "Past greenhouse periods with elevated atmospheric CO2 were characterized by globally warmer sea-surface temperatures (SST). However, the extent to which the high latitudes warmed to a greater degree than the tropics (polar amplification) remains poorly constrained, in particular because there are only a few temperature reconstructions from the tropics. Consequently, the relationship between increased CO2, the degree of tropical warming, and the resulting latitudinal SST gradient is not well known. Here, we present coupled clumped isotope (Δ47)-Mg/Ca measurements of foraminifera from a set of globally distributed sites in the tropics and midlatitudes. Δ47 is insensitive to seawater chemistry and therefore provides a robust constraint on tropical SST. Crucially, coupling these data with Mg/Ca measurements allows the precise reconstruction of Mg/Casw throughout the Eocene, enabling the reinterpretation of all planktonic foraminifera Mg/Ca data. The combined dataset constrains the range in Eocene tropical SST to 30–36 °C (from sites in all basins). We compare these accurate tropical SST to deep-ocean temperatures, serving as a minimum constraint on high-latitude SST. This results in a robust conservative reconstruction of the early Eocene latitudinal gradient, which was reduced by at least 32 ± 10% compared with present day, demonstrating greater polar amplification than captured by most climate models."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #175 on: January 26, 2018, 08:17:41 PM »
Ocean current – hydroclimate interactions merit better calibration as indicated by the linked reference.  This implies that rainfall patterns will likely change as the AMOC continues to slow-down:

Kaustubh Thirumalai et al. (2018), "Pronounced centennial-scale Atlantic Ocean climate variability correlated with Western Hemisphere hydroclimate", Nature Communications 9, Article number: 392, doi:10.1038/s41467-018-02846-4

https://www.nature.com/articles/s41467-018-02846-4

Abstract: "Surface-ocean circulation in the northern Atlantic Ocean influences Northern Hemisphere climate. Century-scale circulation variability in the Atlantic Ocean, however, is poorly constrained due to insufficiently-resolved paleoceanographic records. Here we present a replicated reconstruction of sea-surface temperature and salinity from a site sensitive to North Atlantic circulation in the Gulf of Mexico which reveals pronounced centennial-scale variability over the late Holocene. We find significant correlations on these timescales between salinity changes in the Atlantic, a diagnostic parameter of circulation, and widespread precipitation anomalies using three approaches: multiproxy synthesis, observational datasets, and a transient simulation. Our results demonstrate links between centennial changes in northern Atlantic surface-circulation and hydroclimate changes in the adjacent continents over the late Holocene. Notably, our findings reveal that weakened surface-circulation in the Atlantic Ocean was concomitant with well-documented rainfall anomalies in the Western Hemisphere during the Little Ice Age."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #176 on: February 02, 2018, 11:32:05 PM »
It is important for climate models to correctly account for freshwater hosing, particularly in the Southern Ocean:

Ariaan Purich, Matthew H. England, Wenju Cai, Arnold Sullivan, and Paul J. Durack (2018), "Impacts of broad-scale surface freshening of the Southern Ocean in a coupled climate model", Journal of Climate, https://doi.org/10.1175/JCLI-D-17-0092.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0092.1

Abstract: "The Southern Ocean surface has freshened in recent decades, increasing water column stability and reducing upwelling of warmer subsurface waters. The majority of CMIP5 models underestimate or fail to capture this historical surface freshening, yet little is known about the impact of this model bias on regional ocean circulation and hydrography. Here we perform experiments using a global coupled climate model with additional freshwater applied to the Southern Ocean to assess the influence of recent surface freshening. The simulations explore the impact of persistent and long-term broad-scale freshening due to processes including precipitation minus evaporation changes. Thus, unlike previous studies, the freshening is applied as far north as 55°S, beyond the Antarctic ice margin. We find that imposing a large-scale surface freshening causes a surface cooling and sea-ice increase under pre-industrial conditions, due to a reduction in ocean convection and weakened entrainment of warm subsurface waters into the surface ocean. This is consistent with inter-model relationships between CMIP5 models and our simulations, which suggest that models with larger surface freshening also exhibit stronger surface cooling and increased sea ice. Additional experiments are conducted with surface salinity restoration applied to capture observed regional salinity trends. Remarkably, without any mechanical wind trend forcing, these simulations accurately represent the spatial pattern of observed surface temperature and sea-ice trends around Antarctica. This study highlights the importance of accurately simulating changes in Southern Ocean salinity to capture changes in ocean circulation, sea surface temperature and sea ice."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #177 on: February 02, 2018, 11:32:28 PM »
It is important for climate models to correctly account for Agulhas leakage if they are going to accurately estimate ECS:

Shane Elipot and Lisa M. Beal (2018), "Observed Agulhas Current sensitivity to interannual and long-term trend atmospheric forcings", The Journal of Climate, https://doi.org/10.1175/JCLI-D-17-0597.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0597.1?utm_content=buffer43aa3&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Twenty-nine percent of the interannual variance of the Agulhas Current transport can be linearly related to six modes of Southern Hemisphere atmospheric variability. Agulhas Current transport is quantified by a 24-yr proxy constructed using satellite altimetry and in situ data, while atmospheric variability is represented by two reanalysis products. The two leading modes of atmospheric variability, each explaining 5% of the variance of the Agulhas Current, can be described as a tropical Indo-Pacific mode, strongly correlated to ENSO, and a subtropical-subpolar mode, strongly correlated with the SAM. ENSO alone can explain 11.5% of Agulhas transport variance, yet SAM alone has no significant correlation. The remaining four atmospheric modes are not related to common climate indices and together they explain 19% of Agulhas variance, describing decadal oscillations. In previous studies using reanalyses and climate models it has been suggested that the Agulhas Current is intensifying in response to a strengthening and poleward shift of the Westerlies, expressed by a positive trend in the SAM. Here, we find that, given its apparent weak sensitivity to the SAM, the increase in SAM over the past 24 years does not lead to a detectable trend in Agulhas Current transport."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #178 on: February 06, 2018, 04:13:34 PM »
Here is more paleodata that can be used to better calibrate climate models:

Rehfeld, K. et al. (2018), "Global patterns of declining temperature variability from the Last Glacial Maximum to the Holocene", Nature, https://www.nature.com/articles/nature25454

https://www.nature.com/articles/nature25454

Abstract: "Changes in climate variability are as important for society to address as are changes in mean climate1. Contrasting temperature variability during the Last Glacial Maximum and the Holocene can provide insights into the relationship between the mean state of the climate and its variability2,3. However, although glacial–interglacial changes in variability have been quantified for Greenland2, a global view remains elusive. Here we use a network of marine and terrestrial temperature proxies to show that temperature variability decreased globally by a factor of four as the climate warmed by 3–8 degrees Celsius from the Last Glacial Maximum (around 21,000 years ago) to the Holocene epoch (the past 11,500 years). This decrease had a clear zonal pattern, with little change in the tropics (by a factor of only 1.6–2.8) and greater change in the mid-latitudes of both hemispheres (by a factor of 3.3–14). By contrast, Greenland ice-core records show a reduction in temperature variability by a factor of 73, suggesting influences beyond local temperature or a decoupling of atmospheric and global surface temperature variability for Greenland. The overall pattern of reduced variability can be explained by changes in the meridional temperature gradient, a mechanism that points to further decreases in temperature variability in a warmer future."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #179 on: February 14, 2018, 01:22:50 AM »
The linked reference discusses difficulties with calibrating estimates of climate sensitivity, and makes recommendations for future research on this matter:

Eelco J. Rohling, Gianluca Marino, Gavin L. Foster, Philip A. Goodwin, Anna S. von der Heydt, and Peter Köhler (January 2018, First published as a Review in Advance on September 22, 2017), "Comparing Climate Sensitivity, Past and Present", Annual Review of Marine Science, Vol. 10:261-288, https://doi.org/10.1146/annurev-marine-121916-063242

http://www.annualreviews.org/doi/abs/10.1146/annurev-marine-121916-063242

Abstract: "Climate sensitivity represents the global mean temperature change caused by changes in the radiative balance of climate; it is studied for both present/future (actuo) and past (paleo) climate variations, with the former based on instrumental records and/or various types of model simulations. Paleo-estimates are often considered informative for assessments of actuo-climate change caused by anthropogenic greenhouse forcing, but this utility remains debated because of concerns about the impacts of uncertainties, assumptions, and incomplete knowledge about controlling mechanisms in the dynamic climate system, with its multiple interacting feedbacks and their potential dependence on the climate background state. This is exacerbated by the need to assess actuo- and paleoclimate sensitivity over different timescales, with different drivers, and with different (data and/or model) limitations. Here, we visualize these impacts with idealized representations that graphically illustrate the nature of time-dependent actuo- and paleoclimate sensitivity estimates, evaluating the strengths, weaknesses, agreements, and differences of the two approaches. We also highlight priorities for future research to improve the use of paleo-estimates in evaluations of current climate change."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #180 on: February 27, 2018, 07:13:10 PM »
The linked reference supports other recent research that indicates that decadal climate variability is related to climate sensitivity:

Colman, R. & Power, S.B. (2018), "What can decadal variability tell us about climate feedbacks and sensitivity?", Clim Dyn, https://doi.org/10.1007/s00382-018-4113-7

https://rd.springer.com/article/10.1007%2Fs00382-018-4113-7?utm_content=buffer44f1b&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Radiative feedbacks are known to determine climate sensitivity. Global top-of-atmosphere radiation correlations with surface temperature performed here show that decadal variability in surface temperature is also reinforced by strong positive feedbacks in models, both in the long wave (LW) and short wave (SW), offsetting much of the Planck radiative damping. Net top-of-atmosphere feedback is correlated with the magnitude of decadal temperature variability, particularly in the tropics. This indicates decadal-timescale radiative reinforcement of surface temperature variability. Assuming a simple global ocean mixed layer response, the reinforcement is found to be of a magnitude comparable to that required for typical decadal global scale anomalies. The magnitude of decadal variability in the tropics is uncorrelated with LW feedbacks, but it is correlated with total SW feedbacks, which are, in turn, correlated with tropical SW cloud feedback. Globally, water vapour/lapse rate, surface albedo and cloud feedbacks on decadal timescales are, on average, as strong as those operating under climate change. Together these results suggest that some of the physical processes responsible for setting the magnitude of global temperature change in the twenty-first century and climate sensitivity also help set the magnitude of the natural decadal variability. Furthermore, a statistically significant correlation exists between climate sensitivity and decadal variability in the tropics across CMIP5 models, although this is not apparent in the earlier generation of CMIP3 models. Thus although the link to sensitivity is not conclusive, this opens up potential paths to improve our understanding of climate feedbacks, climate sensitivity and decadal climate variability, and has the potential to reduce the associated uncertainty."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #181 on: March 14, 2018, 05:07:02 PM »
The linked article discusses a new research project, that should provide findings that will help calibrate climate model feedbacks associated with high-latitude NH methane emissions:

Title: "Understanding High-Latitude Methane in a Warming Climate"

https://eos.org/project-updates/understanding-high-latitude-methane-in-a-warming-climate

Extract: "Climate change could spur greenhouse gas release from the Arctic. A new project will synthesize existing data to improve uncertain predictions."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #182 on: March 24, 2018, 04:59:11 PM »
I hope that the linked reference helps to calibrate ESMs to better reflect the importance of wetlands on increasing atmospheric methane concentrations:

Peter O. Hopcroft et al. (2018), "Bayesian analysis of the glacial‐interglacial methane increase constrained by stable isotopes and Earth System modelling", GRL, https://doi.org/10.1002/2018GL077382

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2018GL077382

Abstract: "The observed rise in atmospheric methane (CH4) from 375 ppbv during the last glacial maximum (LGM: 21,000 yr ago) to 680 ppbv during the late pre‐industrial era is not well understood. Atmospheric chemistry considerations implicate an increase in CH4 sources, but process‐based estimates fail to reproduce the required amplitude. CH4 stable isotopes provide complementary information that can help constrain the underlying causes of the increase. We combine Earth System model simulations of the late pre‐industrial and LGM CH4 cycles, including process‐based estimates of the isotopic discrimination of vegetation, in a box‐model of atmospheric CH4 and its isotopes. Using a Bayesian approach, we show how model‐based constraints and ice core observations may be combined in a consistent probabilistic framework. The resultant posterior distributions point to a strong reduction in wetland and other biogenic CH4 emissions during the LGM, with a modest increase in the geological source, or potentially natural or anthropogenic fires, accounting for the observed enrichment of δ13CH4."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #183 on: March 24, 2018, 05:05:19 PM »
I hope that the linked research is used to better calibrate ESMs w.r.t. the nonlinear interaction between Arctic sea ice extent and incursions of Atlantic water across the Greenland-Scotland Ridge:

Mari F. Jensen et al. (2018), "Large changes in sea ice triggered by small changes in Atlantic water temperature", The Journal of Climate, https://doi.org/10.1175/JCLI-D-17-0802.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0802.1

Abstract: "The sensitivity of sea ice to the temperature of inflowing Atlantic water across the Greenland-Scotland Ridge is investigated using an eddy-resolving configuration of the Massachusetts Institute of Technology general circulation model with idealized topography. During the last glacial period, when climate on Greenland is known to have been extremely unstable, sea ice is thought to have covered the Nordic Seas. The dramatic excursions in climate during this period, seen as large abrupt warming events on Greenland and known as Dansgaard-Oeschger events (DO events), are proposed to have been caused by a rapid retreat of Nordic Seas sea ice. Here, we show that a full sea-ice cover and Arctic-like stratification can exist in the Nordic Seas given a sufficiently cold Atlantic inflow and corresponding low transport of heat across the Greenland-Scotland Ridge. Once sea ice is established, continued sea-ice formation and melt efficiently freshens the surface ocean and makes the deeper layers more saline. This creates a strong salinity stratification in the Nordic Seas, similar to today’s Arctic Ocean, with a cold fresh surface layer protecting the overlying sea ice from the warm Atlantic water below. There is a non-linear response in Nordic Seas sea ice to Atlantic water temperature with simulated large abrupt changes in sea ice given small changes in inflowing temperature. This suggests that the DO events were more likely to have occurred during periods of reduced warm Atlantic water inflow to the Nordic Seas."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #184 on: March 30, 2018, 10:36:13 PM »
Preliminary calibration of E3SM to MOFLUX indicate that "… modelling soil respiration can be significantly improved by better model representations of the soil water retention curve."

Liang, J., Wang, G., Ricciuto, D. M., Gu, L., Hanson, P. J., Wood, J. D., and Mayes, M. A.: Evaluating the E3SM Land Model at a temperate forest site using flux and soil water measurements, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2018-34, in review, 2018.

https://www.geosci-model-dev-discuss.net/gmd-2018-34/

Abstract. Accurate simulations of soil respiration and carbon dioxide (CO2) efflux are critical to project global biogeochemical cycles and the magnitude of carbon (C) feedbacks to climate change in Earth system models (ESMs). Currently, soil respiration is not represented well in ESMs, and few studies have attempted to address this deficiency. In this study, we evaluated the simulation of soil respiration in the Energy Exascale Earth System Model (E3SM) using long-term observations from the Missouri Ozark AmeriFlux (MOFLUX) forest site in the central U.S. Simulations using the default model parameters significantly underestimated annual soil respiration and gross primary production, while underestimating soil water potential during growing seasons and overestimating it during non-growing seasons. A site-specific soil water retention curve significantly improved modelled soil water potential, gross primary production and soil respiration. However, the model continued to underestimate soil respiration during peak growing seasons, and overestimate soil respiration during non-peak growing seasons. One potential reason may be that the current model does not adequately represent the seasonal cycle of microbial organisms and soil macroinvertebrates, which have high biomass and activity during peak growing seasons and tend to be dormant during non-growing seasons. Our results confirm that modelling soil respiration can be significantly improved by better model representations of the soil water retention curve.
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #185 on: April 02, 2018, 08:38:39 PM »
The linked open access reference discusses technical considerations of using energy-balance frameworks to estimate the impacts of radiative feedback mechanisms:

Proistosescu, C., Donohoe, A., Armour, K., Roe, G. H., Stuecker, M. F., & Bitz, C. M. (2018, March 2), "Radiative feedbacks from stochastic variability in surface temperature and radiative imbalance", http://doi.org/10.17605/OSF.IO/5DSBF

https://eartharxiv.org/5dsbf

Abstract: "Estimates of radiative feedbacks obtained by regressing fluctuations in top-of-atmosphere (TOA) energy imbalance and surface temperature depend critically on assumptions about the nature of the stochastic forcing and on the sampling interval. Here we develop an energy-balance framework that allows us to model the different contributions of stochastic atmospheric and oceanic forcing on feed- back estimates. The contribution of different forcing components are parsed based on their impacts on the covariance structure of temperature and TOA energy fluxes, and the framework is validated in a hierarchy of climate model simulations that span a range of oceanic configurations and reproduce the key features seen in observations. We find that at least three distinct forcing sources, feedbacks, and time scales are needed to explain the full covariance structure. Atmospheric and oceanic forcings drive modes of variability with distinct relationships between near-surface air temperature and TOA radiation, and the net regression-based feedback estimate is found to be a weighted average of the distinct feedbacks associated with each mode. Moreover, the estimated feedback depends on whether surface temperature and TOA energy fluxes are sampled at monthly or annual timescales. The results suggest that regression-based feedback estimates reflect contributions from a combination of stochastic forcings, and should not be interpreted as providing an estimate of the radiative feedback governing the climate response to greenhouse gas forcing."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #186 on: April 02, 2018, 11:52:55 PM »
The linked reference discusses ten years (2002 to 2012) of observational measurement of Earth's surface radiative forcing from atmospheric methane.  Such measurements can be used to better calibrate ESM projections:

D. R. Feldman, W. D. Collins, S. C. Biraud, M. D. Risser, D. D. Turner, P. J. Gero, J. Tadić, D. Helmig, S. Xie, E. J. Mlawer, T. R Shippert & M. S. Torn. Observationally derived rise in methane surface forcing mediated by water vapour trends. Nature Geoscience, 2018 DOI: 10.1038/s41561-018-0085-9

https://www.nature.com/articles/s41561-018-0085-9

Abstract: "Atmospheric methane (CH4) mixing ratios exhibited a plateau between 1995 and 2006 and have subsequently been increasing. While there are a number of competing explanations for the temporal evolution of this greenhouse gas, these prominent features in the temporal trajectory of atmospheric CH4 are expected to perturb the surface energy balance through radiative forcing, largely due to the infrared radiative absorption features of CH4. However, to date this has been determined strictly through radiative transfer calculations. Here, we present a quantified observation of the time series of clear-sky radiative forcing by CH4 at the surface from 2002 to 2012 at a single site derived from spectroscopic measurements along with line-by-line calculations using ancillary data. There was no significant trend in CH4 forcing between 2002 and 2006, but since then, the trend in forcing was 0.026 ± 0.006 (99.7% CI) W m2 yr−1. The seasonal-cycle amplitude and secular trends in observed forcing are influenced by a corresponding seasonal cycle and trend in atmospheric CH4. However, we find that we must account for the overlapping absorption effects of atmospheric water vapour (H2O) and CH4 to explain the observations fully. Thus, the determination of CH4 radiative forcing requires accurate observations of both the spatiotemporal distribution of CH4 and the vertically resolved trends in H2O."

See also:

Title: "First direct observations of methane's increasing greenhouse effect at the Earth's surface"

https://www.sciencedaily.com/releases/2018/04/180402123305.htm

Extract: "Scientists have directly measured the increasing greenhouse effect of methane at the Earth's surface for the first time. A research team has tracked a rise in the warming effect of methane - one of the most important greenhouse gases for the Earth's atmosphere - over a 10-year period.

The researchers believe this type of direct field observation can provide a more accurate and complete picture of the relationship between atmospheric greenhouse gas concentrations and their warming effect on Earth's surface."
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Re: Climate Model Test Beds: Calibrating Nonlinear ESMs focused on E3SM/ACME
« Reply #187 on: April 25, 2018, 12:20:26 AM »
Information such as that in the linked reference can be used to better calibrate advanced climate models:

Nijsse, F. J. M. M. and Dijkstra, H. A.: A mathematical approach to understanding emergent constraints, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2018-15, in review, 2018.

https://www.earth-syst-dynam-discuss.net/esd-2018-15/

Abstract. One of the approaches to constrain uncertainty in climate models is the identification of emergent constraints. These are physically explainable empirical relationships between a particular simulated characteristic of the current climate versus future climate change from an ensemble of climate models, which can be exploited using current observations. In this paper, we develop a theory to understand the appearance of such emergent constraints. Based on this theory, we also propose a classification for emergent constraints and applications are shown for several idealized climate models.
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The DOE has now released computer code & preliminary results from ACME (Accelerated Climate Model for Energy) while the DOE has renamed the program E3SM (Energy Exascale Earth System Model), and this world's most sophisticated climate model projects that ECS for the rest of this century will be about 5.2C (& this relatively high value is likely attributable to the state-of-the-art way that ACME/E3SM models aerosols and cloud feedback mechanisms).

While some consensus scientists (like Bjorn Stevens) have said that it is difficult to determine whether the ACME findings are any more relevant than other models in the CMIP6 program; I believe that these findings from the world's most advanced ESM warrant the adoptions of the Precautionary Principle, particularly as the ACME results only partially address Hansen's ice-climate feedback mechanism:

Title: "DOE’s maverick climate model is about to get its first test"
doi:10.1126/science.aau0578

http://www.sciencemag.org/news/2018/05/does-maverick-climate-model-about-get-its-first-test

Extract: "In 2017, after President Donald Trump took office and pulled the nation out of the Paris climate accords, DOE dropped "climate" from the project name. The new name, the Energy Exascale Earth System Model (E3SM), better reflects the model's focus on the entire Earth system, says project leader David Bader of Lawrence Livermore National Laboratory in California.
..
One preliminary result, on the climate's sensitivity to carbon dioxide (CO2), will "raise some eyebrows," Bader says. Most models estimate that, for a doubling of CO2 above preindustrial levels, average global temperatures will rise between 1.5°C and 4.5°C. The E3SM predicts a strikingly high rise of 5.2°C, which Leung suspects is due to the way the model handles aerosols and clouds. And like many models, the E3SM produces two bands of rainfall in the tropics, rather than the one seen in nature near the equator.

The first test of the E3SM will be its performance in CMIP6. Nearly three dozen modeling groups, including newcomers from South Korea, India, Brazil, and South Africa, are expected to submit results to the intercomparison between now and 2020."

Edit, see also:

https://gcn.com/articles/2018/04/26/e3sm-earth-model.aspx

&

https://www.llnl.gov/news/new-exascale-system-earth-simulation

Edit2, see also:

Title: "SimEarth"

https://phys.org/news/2018-05-simearth.html

Extract: ""With this new system, we'll be able to more realistically simulate the present, which gives us more confidence to simulate the future," says David Bader, computational scientist at Lawrence Livermore National Laboratory and overall E3SM project lead."
« Last Edit: May 08, 2018, 12:20:30 AM by AbruptSLR »
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The finding from the linked reference can be used to improve the calibration of advanced ESMs:

Claire E. Huck et al. (11 June 2017), "Antarctic climate, Southern Ocean circulation patterns, and deep water formation during the Eocene", Paleoceanography and Paleoclimatology, https://doi.org/10.1002/2017PA003135

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017PA003135

Abstract: "We assess early‐to‐middle Eocene seawater neodymium (Nd) isotope records from seven Southern Ocean deep‐sea drill sites to evaluate the role of Southern Ocean circulation in long‐term Cenozoic climate change. Our study sites are strategically located on either side of the Tasman Gateway and are positioned at a range of shallow (<500 m) to intermediate/deep (~1000–2500 m) paleowater depths. Unradiogenic seawater Nd isotopic compositions, reconstructed from fish teeth at intermediate/deep Indian Ocean pelagic sites (Ocean Drilling Program (ODP) Sites 738 and 757 and Deep Sea Drilling Project (DSDP) Site 264), indicate a dominant Southern Ocean‐sourced contribution to regional deep waters (εNd(t) = −9.3 ± 1.5). IODP Site U1356 off the coast of Adélie Land, a locus of modern‐day Antarctic Bottom Water production, is identified as a site of persistent deep water formation from the early Eocene to the Oligocene. East of the Tasman Gateway an additional local source of intermediate/deep water formation is inferred at ODP Site 277 in the SW Pacific Ocean (εNd(t) = −8.7 ± 1.5). Antarctic‐proximal shelf sites (ODP Site 1171 and Site U1356) reveal a pronounced erosional event between 49 and 48 Ma, manifested by ~2 εNd unit negative excursions in seawater chemistry toward the composition of bulk sediments at these sites. This erosional event coincides with the termination of peak global warmth following the Early Eocene Climatic Optimum and is associated with documented cooling across the study region and increased export of Antarctic deep waters, highlighting the complexity and importance of Southern Ocean circulation in the greenhouse climate of the Eocene."
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The linked reference indicates that terrestrial carbon sinks degrade more quickly when starting increased radiative forcing from pre-industrial conditions than from glacial conditions.  Thus Earth System Models, that were calibrated based on paleo data, should be recalibrated to expect faster loss of terrestrial carbon sinks for the rest of this century:

Adloff, M., Reick, C. H., and Claussen, M.: Earth system model simulations show different feedback strengths of the terrestrial carbon cycle under glacial and interglacial conditions, Earth Syst. Dynam., 9, 413-425, https://doi.org/10.5194/esd-9-413-2018, 2018.

https://www.earth-syst-dynam.net/9/413/2018/

Abstract. In simulations with the MPI Earth System Model, we study the feedback between the terrestrial carbon cycle and atmospheric CO2 concentrations under ice age and interglacial conditions. We find different sensitivities of terrestrial carbon storage to rising CO2 concentrations in the two settings. This result is obtained by comparing the transient response of the terrestrial carbon cycle to a fast and strong atmospheric CO2 concentration increase (roughly 900 ppm) in Coupled Climate Carbon Cycle Model Intercomparison Project (C4MIP)-type simulations starting from climates representing the Last Glacial Maximum (LGM) and pre-industrial times (PI). In this set-up we disentangle terrestrial contributions to the feedback from the carbon-concentration effect, acting biogeochemically via enhanced photosynthetic productivity when CO2 concentrations increase, and the carbon–climate effect, which affects the carbon cycle via greenhouse warming. We find that the carbon-concentration effect is larger under LGM than PI conditions because photosynthetic productivity is more sensitive when starting from the lower, glacial CO2 concentration and CO2 fertilization saturates later. This leads to a larger productivity increase in the LGM experiment. Concerning the carbon–climate effect, it is the PI experiment in which land carbon responds more sensitively to the warming under rising CO2 because at the already initially higher temperatures, tropical plant productivity deteriorates more strongly and extratropical carbon is respired more effectively. Consequently, land carbon losses increase faster in the PI than in the LGM case. Separating the carbon–climate and carbon-concentration effects, we find that they are almost additive for our model set-up; i.e. their synergy is small in the global sum of carbon changes. Together, the two effects result in an overall strength of the terrestrial carbon cycle feedback that is almost twice as large in the LGM experiment as in the PI experiment. For PI, ocean and land contributions to the total feedback are of similar size, while in the LGM case the terrestrial feedback is dominant.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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The linked article discusses one of the efforts to reduce uncertainties w.r.t. biogeochemistry and land processes in the E3SM projections:

Daniel Ricciuto et al. (27 December 2017), "The Impact of Parametric Uncertainties on Biogeochemistry in the E3SM Land Model", JAMES, Vol 10, Issue 2, https://doi.org/10.1002/2017MS000962

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017MS000962

Abstract: "We conduct a global sensitivity analysis (GSA) of the Energy Exascale Earth System Model (E3SM), land model (ELM) to calculate the sensitivity of five key carbon cycle outputs to 68 model parameters. This GSA is conducted by first constructing a Polynomial Chaos (PC) surrogate via new Weighted Iterative Bayesian Compressive Sensing (WIBCS) algorithm for adaptive basis growth leading to a sparse, high‐dimensional PC surrogate with 3,000 model evaluations. The PC surrogate allows efficient extraction of GSA information leading to further dimensionality reduction. The GSA is performed at 96 FLUXNET sites covering multiple plant functional types (PFTs) and climate conditions. About 20 of the model parameters are identified as sensitive with the rest being relatively insensitive across all outputs and PFTs. These sensitivities are dependent on PFT, and are relatively consistent among sites within the same PFT. The five model outputs have a majority of their highly sensitive parameters in common. A common subset of sensitive parameters is also shared among PFTs, but some parameters are specific to certain types (e.g., deciduous phenology). The relative importance of these parameters shifts significantly among PFTs and with climatic variables such as mean annual temperature."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Hopefully, climate modelers will use such paleo data to address the influence of snow albedo regarding the potential for rapid ice sheet retreat in the coming decades:

Willeit, M. and Ganopolski, A.: The importance of snow albedo for ice sheet evolution over the last glacial cycle, Clim. Past, 14, 697-707, https://doi.org/10.5194/cp-14-697-2018, 2018.

https://www.clim-past.net/14/697/2018/

Abstract. The surface energy and mass balance of ice sheets strongly depends on the amount of solar radiation absorbed at the surface, which is mainly controlled by the albedo of snow and ice. Here, using an Earth system model of intermediate complexity, we explore the role played by surface albedo for the simulation of glacial cycles. We show that the evolution of the Northern Hemisphere ice sheets over the last glacial cycle is very sensitive to the representation of snow albedo in the model. It is well known that the albedo of snow depends strongly on snow grain size and the content of light-absorbing impurities. Excluding either the snow aging effect or the dust darkening effect on snow albedo leads to an excessive ice build-up during glacial times and consequently to a failure in simulating deglaciation. While the effect of snow grain growth on snow albedo is well constrained, the albedo reduction due to the presence of dust in snow is much more uncertain because the light-absorbing properties of dust vary widely as a function of dust mineral composition. We also show that assuming slightly different optical properties of dust leads to very different ice sheet and climate evolutions in the model. Conversely, ice sheet evolution is less sensitive to the choice of ice albedo in the model. We conclude that a proper representation of snow albedo is a fundamental prerequisite for a successful simulation of glacial cycles.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Hopefully, governments will provide sufficient funding to support the recommended drilling program to test for past WAIS collapse.  Such information would be useful for the calibration of ESMs w.r.t. freshwater hosing and the ice-climate feedback mechanism:

Spector, P., Stone, J., Pollard, D., Hillebrand, T., Lewis, C., and Gombiner, J.: West Antarctic sites for subglacial drilling to test for past ice-sheet collapse, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-88, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-88/

Abstract. Mass loss from the West Antarctic Ice Sheet (WAIS) is increasing, and there is concern that an incipient large-scale deglaciation of the marine basins may already be underway. Measurements of cosmogenic nuclides in subglacial bedrock surfaces have the potential to establish whether and when the marine-based portions of the WAIS deglaciated in the past. However, because most of the bedrock revealed by ice-sheet collapse would remain below sea level, shielded from the cosmic-ray flux, drill sites for subglacial sampling must be located in areas where thinning of the residual ice sheet would expose presently subglacial bedrock surfaces. In this paper we discuss the criteria and considerations for choosing drill sites where subglacial samples will provide maximum information about WAIS extent during past interglacial periods. We evaluate candidate sites in West Antarctica and find that sites located adjacent to the large marine basins of West Antarctica will be most diagnostic of past ice-sheet collapse. There are important considerations for drill-site selection on the kilometer scale that can only be assessed by field reconnaissance. As a case study of these considerations, we describe reconnaissance at sites in West Antarctica, focusing on the Pirrit Hills, where in the summer of 2016–2017, an 8 m bedrock core was retrieved from below 150 m of ice.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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When mainly the satellite data is processed using new & improved algorithms the 'observed' temperature trends from 1979 to 2005 move closer to the model projections.  By extension this implies that the AR5 ECS values are too low:

Amanda C. Maycock et al. (04 June 2018), "Revisiting the mystery of recent stratospheric temperature trends", Geophysical Research Letters,  https://doi.org/10.1029/2018GL078035

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL078035

"Abstract
Simulated stratospheric temperatures over the period 1979‐2016 in models from the Chemistry‐Climate Model Initiative (CCMI) are compared with recently updated and extended satellite observations. The multi‐model mean global temperature trends over 1979‐2005 are ‐0.88 ± 0.23, ‐0.70 ± 0.16, and ‐0.50 ± 0.12 K decade‐1 for the Stratospheric Sounding Unit (SSU) channels 3 (~40‐50 km), 2 (~35‐45 km), and 1 (~25‐35 km), respectively. These are within the uncertainty bounds of the observed temperature trends from two reprocessed satellite datasets. In the lower stratosphere, the multi‐model mean trend in global temperature for the Microwave Sounding Unit channel 4 (~13‐22 km) is ‐0.25 ± 0.12 K decade‐1 over 1979‐2005, consistent with estimates from three versions of this satellite record. The simulated stratospheric temperature trends in CCMI models over 1979‐2005 agree with the previous generation of chemistry‐climate models. The models and an extended satellite dataset of SSU with the Advanced Microwave Sounding Unit‐A show weaker global stratospheric cooling over 1998‐2016 compared to the period of intensive ozone depletion (1979‐1997). This is due to the reduction in ozone‐induced cooling from the slow‐down of ozone trends and the onset of ozone recovery since the late 1990s. In summary, the results show much better consistency between simulated and satellite observed stratospheric temperature trends than was reported by Thompson et al. (2012) for the previous versions of the SSU record and chemistry‐climate models. The improved agreement mainly comes from updates to the satellite records; the range of simulated trends is comparable to the previous generation of models.
Plain Language Summary
A previous analysis by Thompson et al. (2012) showed substantial differences between satellite observed and model simulated stratospheric cooling trends since the late 1970s. Here we compare recently revised and extended satellite temperature records with new simulations from 14 chemistry‐climate models. The results show much better agreement in the magnitude of stratospheric cooling over 1979‐2005 between models and observations. This cooling was driven by both increasing greenhouse gases and declining stratospheric ozone levels. An extended satellite temperature record and the models show weaker global stratospheric cooling over 1998‐2016 compared to 1979‐1997. This is due to the reduction in ozone‐induced cooling from the slow‐down of ozone trends and the onset of ozone recovery since the late 1990s. There are larger differences in the latitudinal structure of past stratospheric temperature trends due to the effects of unforced atmospheric variability. In summary, the results show much better consistency between simulated and satellite observed stratospheric temperature trends than was reported by Thompson et al. (2012) for the previous versions of the satellite record and last generation of chemistry‐climate models. The improved agreement mainly comes from updates to the satellite records, while the range of simulated trends is comparable to the previous generation of models."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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The linked reference discusses the finding of improved modeling near the Eocene–Oligocene transition (EOT) that are of particular interest for calibrating climate models to including Hansen's ice-climate feedback mechanism (that is highly related to the response of the meridional overturning circulation).  These new finding indicate higher climate sensitivity than projected by earlier (as in those used by AR5) less-sophisticated models.  These findings increase the probability that Hansen's warnings about the risks of abrupt climate change this century are correct:

Hutchinson, D. K., de Boer, A. M., Coxall, H. K., Caballero, R., Nilsson, J., and Baatsen, M.: Climate sensitivity and meridional overturning circulation in the late Eocene using GFDL CM2.1, Clim. Past, 14, 789-810, https://doi.org/10.5194/cp-14-789-2018, 2018.

https://www.clim-past.net/14/789/2018/

Abstract. The Eocene–Oligocene transition (EOT), which took place approximately 34 Ma ago, is an interval of great interest in Earth's climate history, due to the inception of the Antarctic ice sheet and major global cooling. Climate simulations of the transition are needed to help interpret proxy data, test mechanistic hypotheses for the transition and determine the climate sensitivity at the time. However, model studies of the EOT thus far typically employ control states designed for a different time period, or ocean resolution on the order of 3°. Here we developed a new higher resolution palaeoclimate model configuration based on the GFDL CM2.1 climate model adapted to a late Eocene (38 Ma) palaeogeography reconstruction. The ocean and atmosphere horizontal resolutions are 1°  ×  1.5° and 3°  ×  3.75° respectively. This represents a significant step forward in resolving the ocean geography, gateways and circulation in a coupled climate model of this period. We run the model under three different levels of atmospheric CO2: 400, 800 and 1600 ppm. The model exhibits relatively high sensitivity to CO2 compared with other recent model studies, and thus can capture the expected Eocene high latitude warmth within observed estimates of atmospheric CO2. However, the model does not capture the low meridional temperature gradient seen in proxies. Equatorial sea surface temperatures are too high in the model (30–37 °C) compared with observations (max 32 °C), although observations are lacking in the warmest regions of the western Pacific. The model exhibits bipolar sinking in the North Pacific and Southern Ocean, which persists under all levels of CO2. North Atlantic surface salinities are too fresh to permit sinking (25–30 psu), due to surface transport from the very fresh Arctic ( ∼  20 psu), where surface salinities approximately agree with Eocene proxy estimates. North Atlantic salinity increases by 1–2 psu when CO2 is halved, and similarly freshens when CO2 is doubled, due to changes in the hydrological cycle.
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These findings indicate that the implications of paleo records on the calibration of impacts of Hansen's ice-climate feedback mechanism on paleo-climate model projections, need to be revised:

R. F. Ivanovic et al. (04 June 2018), "Climatic Effect of Antarctic Meltwater Overwhelmed by Concurrent Northern Hemispheric Melt", Geophysical Research Letters, https://doi.org/10.1029/2018GL077623

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL077623

Abstract
Records indicate that 14,500 years ago, sea level rose by 12–22 m in under 340 years. However, the source of the sea level rise remains contentious, partly due to the competing climatic impact of different hemispheric contributions. Antarctic meltwater could indirectly strengthen the Atlantic Meridional Overturning Circulation (AMOC), causing northern warming, whereas Northern Hemisphere ice sheet meltwater has the opposite effect. This story has recently become more intriguing, due to increasing evidence for sea level contributions from both hemispheres. Using a coupled climate model with freshwater forcing, we demonstrate that the climatic influence of southern‐sourced meltwater is overridden by northern sources even when the Antarctic flux is double the North American contribution. This is because the Southern Ocean is quickly resalinized by Antarctic Circumpolar water. These results imply that the pattern of surface climate changes caused by ice sheet melting cannot be used to fingerprint the hemispheric source of the meltwater.
Plain Language Summary
The fastest major sea level rise ever recorded took place 14,500 years ago, when sea level rose by 12–22 m in under 340 years. The extra water came from melting ice sheets, which stretched across North America and northern Europe as well as Greenland and Antarctica. We ran a climate model to test the impact of different meltwater contributions from Antarctica and the Northern Hemisphere ice sheets (North America, Greenland, and Eurasia). Our simulations demonstrate that northern meltwater has a much stronger and longer lasting effect on ocean circulation and climate than Southern Hemisphere melt. Consequently, northern melting overrides the impact of southern melting even when the flux of water from North America is only half the magnitude of the Antarctic flux. This means that past climate records cannot be used to identify the contribution of meltwater from different ice sheets: the northern signal can override the southern signal.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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While the linked research, indicating more rapid bedrock uplift in Amundsen Sea Embayment, seems like good news, if one refers to projections from ice sheet models that do not include Pollard's & DeConto's ice cliff and hydrofacturing mechanism and which assume radiative forcing scenarios of RCP 4.5 or less.  However, if one assumes radiative forcing scenarios close to BAU for the next two decades and projections from Pollard & DeConto's recent work, then Barletta et al (2018)'s finding are actually bad news regarding the potential collapse of the WAIS this century.

V.R. Barletta el al. (22 Jun 2018), "Observed rapid bedrock uplift in Amundsen Sea Embayment promotes ice-sheet stability," Science,:
Vol. 360, Issue 6395, pp. 1335-1339, DOI: 10.1126/science.aao1447.

http://science.sciencemag.org/content/360/6395/1335

Abstract
The marine portion of the West Antarctic Ice Sheet (WAIS) in the Amundsen Sea Embayment (ASE) accounts for one-fourth of the cryospheric contribution to global sea-level rise and is vulnerable to catastrophic collapse. The bedrock response to ice mass loss, glacial isostatic adjustment (GIA), was thought to occur on a time scale of 10,000 years. We used new GPS measurements, which show a rapid (41 millimeters per year) uplift of the ASE, to estimate the viscosity of the mantle underneath. We found a much lower viscosity (4 × 1018 pascal-second) than global average, and this shortens the GIA response time scale from tens to hundreds of years. Our finding requires an upward revision of ice mass loss from gravity data of 10% and increases the potential stability of the WAIS against catastrophic collapse.


Title: "Bedrock in West Antarctica rising at surprisingly rapid rate"

https://phys.org/news/2018-06-bedrock-west-antarctica-surprisingly-rapid.html
Extract: "The findings, reported in the journal Science, have surprising and positive implications for the survival of the West Antarctic Ice Sheet (WAIS), which scientists had previously thought could be doomed because of the effects of climate change.

The unexpectedly fast rate of the rising earth may markedly increase the stability of the ice sheet against catastrophic collapse due to ice loss, scientists say.

Moreover, the rapid rise of the earth in this area also affects gravity measurements, which implies that up to 10 percent more ice has disappeared in this part of Antarctica than previously assumed.

Researchers led by scientists at The Ohio State University used a series of six GPS stations (part of the POLENET-ANET array) attached to bedrock around the Amundsen Sea Embayment to measure its rise in response to thinning ice.

The "uplift rate" was measured at up to 41 millimeters (1.6 inches) a year, said Terry Wilson, one of the leaders of the study and a professor emeritus of earth sciences at Ohio State.

In contrast, places like Iceland and Alaska, which have what are considered rapid uplift rates, generally are measured rising 20 to 30 millimeters a year.
"The rate of uplift we found is unusual and very surprising. It's a game changer," Wilson said.

And it is only going to get faster. The researchers estimate that in 100 years, uplift rates at the GPS sites will be 2.5 to 3.5 times more rapid than currently observed.

While modeling studies have shown that bedrock uplift could theoretically protect WAIS from collapse, it was believed that the process would take too long to have practical effects.

"We previously thought uplift would occur over thousands of years at a very slow rate, not enough to have a stabilizing effect on the ice sheet. Our results suggest the stabilizing effect may only take decades," Wilson said.

Wilson said the rapid rise of the bedrock in this part of Antarctica suggests that the geology underneath Antarctica is different from what scientists had previously believed.

Some scientists suggest that WAIS may have passed a tipping point in which ice loss can no longer be stopped, which could be catastrophic, Wilson said. The glaciers there contain enough water to raise global sea levels up to four feet.

The problem is that much of this area of Antarctica is below sea level. Relatively warm ocean water has flowed in underneath the bottom of the ice sheet, causing thinning and moving the grounding line—where the water, ice and solid earth meet—further inland.

The process seemed unstoppable, Wilson said. "But we found feedbacks that could slow or even stop the process."

One important feedback involves "pinning points—elevated features of the earth rising from the surface below the grounding line that pin the ice sheet to solid earth. These pinning points are going up in response to the uplift of the earth and could prevent further retreat of the ice sheet.

Another feedback is lowering sea levels. Massive ice sheets along the ocean have their own gravitational pull and raise the sea level near them. But as the ice thins and retreats, the gravitational pull lessens and the sea level near the coast goes down.

"The lowering of the sea level, the rising of pinning points and the decrease of the inland slope due to the uplift of the bedrock are all feedbacks that can stabilize the ice sheet," Wilson said.

Other researchers had estimated how much the earth would have to rise to protect WAIS given a range of future climate warming scenarios.

Results of this study estimate that the bedrock at the Pine Island Glacier grounding line (which is part of WAIS) will have risen about 8 meters in 100 years. That is about three times higher than values shown by others to reduce run-away retreat in this area.

"Under many realistic climate models, this should be enough to stabilize the ice sheet," Wilson said.

She said while this study delivers some potentially good news for the Amundsen Sea Embayment, that doesn't mean all is well in Antarctica.

"The physical geography of Antarctica is very complex. We found some potentially positive feedbacks in this area, but other areas could be different and have negative feedbacks instead," she said. Regardless of feedbacks, models suggest that the WAIS will collapse if future global warming is large."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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More input for better calibration of climate models:

Kittel, C., Amory, C., Agosta, C., Delhasse, A., Huot, P.-V., Fichefet, T., and Fettweis, X.: Sensitivity of the current Antarctic surface mass balance to sea surface conditions using MAR, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-106, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-106/

Abstract. Estimates for the recent period and projections of the Antarctic surface mass balance (SMB) often rely on high-resolution polar-oriented regional climate models (RCMs). However, RCMs require large-scale boundary forcing fields provided by reanalyses or general circulation models (GCMs). Since the recent variability of sea surface conditions (SSC, namely sea ice concentration (SIC) and sea surface temperature (SST)) over the Southern Ocean are not reproduced by most GCMs from the 5th phase of the Coupled Model Intercomparison Project (CMIP5) for the last decades, RCMs are then subject to potential biases. We investigate here the direct sensitivity of the Antarctic SMB to SSC perturbations around the Antarctic. With the RCM MAR, different sensitivity experiments are performed over 1979–2015 by altering the ERA-Interim SSC with (i) homogeneous perturbations and (ii) mean anomalies estimated from all CMIP5 models and two extreme ones, while atmospheric lateral boundary conditions remained unchanged. Results show increased (resp. decreased) precipitation due to perturbations inducing warmer (resp. colder) SSC than ERA-Interim significantly altering the SMB of coastal areas, as precipitation is mainly related to cyclones that do not penetrate far into the continent. At the continental scale, significant SMB anomalies (i.e, greater than the interannual variability) are found for the largest combined SST/SIC perturbations. Sensitivity experiments with warmer SSC reveal integrated SMB anomalies (+5 %–+13 %) over the present climate (1979–2015) in the lower range of the SMB increase projected for the end of the 21st century.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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The linked paleo findings should help researchers to calibrate future advanced Earth System Models to better account for possible future freshwater hosing events (like a possibly abrupt collapse of the WAIS this century):

Title: "Fingerprint of ancient abrupt climate change found in Arctic"

https://phys.org/news/2018-07-fingerprint-ancient-abrupt-climate-arctic.html

Extract: "A research team led by Woods Hole Oceanographic Institution (WHOI) found the fingerprint of a massive flood of fresh water in the western Arctic, thought to be the cause of an ancient cold snap that began around 13,000 years ago.

"This abrupt climate change—known as the Younger Dryas—ended more than 1,000 years of warming," explains Lloyd Keigwin, an oceanographer at WHOI and lead author of the paper published online July 9, 2018, in the journal Nature Geoscience.

The cause of the cooling event, which is named after a flower (Dryas octopetala) that flourished in the cold conditions in Europe throughout the time, has remained a mystery and a source of debate for decades.

Many researchers believed the source was a huge influx of freshwater from melting ice sheets and glaciers that gushed into the North Atlantic, disrupting the deep-water circulation system—Atlantic Meridional Overturning Circulation (AMOC)— that transports warmer waters and releases heat to the atmosphere. However, geologic evidence tracing its exact path had been lacking.

In 2013, a team of researchers from WHOI, Scripps Institution of Oceanography at the University of California San Diego, and Oregon State University, set sail to the eastern Beaufort Sea in search of evidence for the flood near where the Mackenzie River enters the Arctic Ocean, forming the border between Canada's Yukon and Northwest territories. From aboard the U.S. Coast Guard Cutter Healy, the team gathered sediment cores from along the continental slope east of the Mackenzie River. After analyzing the shells of fossil plankton found in the sediment cores, they found the long sought-after geochemical signal from the flood."


See also:

Keigwin et al. (2018), "Deglacial floods in the Beaufort Sea preceded Younger Dryas cooling", Nature Geoscience, DOI: 10.1038/s41561-018-0169-6 ,

 http://www.nature.com/articles/s41561-018-0169-6
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson