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Author Topic: Modelling the Anthropocene  (Read 32371 times)

AbruptSLR

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Re: Modelling the Anthropocene
« Reply #150 on: August 22, 2017, 05:51:50 PM »
The linked references discusses the level of modeling effort recommended to reduce uncertainty of projecting future changes in the ENSO due to internal variability:

Xiao-Tong Zheng, Chang Hui & Sang-Wook Yeh (2017), "Response of ENSO amplitude to global warming in CESM large ensemble: uncertainty due to internal variability", Climate Dynamics, pp 1–17, https://doi.org/10.1007/s00382-017-3859-7

https://rd.springer.com/article/10.1007%2Fs00382-017-3859-7?utm_content=bufferc17f2&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "El Niño–Southern Oscillation (ENSO) is the dominant mode of variability in the coupled ocean-atmospheric system. Future projections of ENSO change under global warming are highly uncertain among models. In this study, the effect of internal variability on ENSO amplitude change in future climate projections is investigated based on a 40-member ensemble from the Community Earth System Model Large Ensemble (CESM-LE) project. A large uncertainty is identified among ensemble members due to internal variability. The inter-member diversity is associated with a zonal dipole pattern of sea surface temperature (SST) change in the mean along the equator, which is similar to the second empirical orthogonal function (EOF) mode of tropical Pacific decadal variability (TPDV) in the unforced control simulation. The uncertainty in CESM-LE is comparable in magnitude to that among models of the Coupled Model Intercomparison Project phase 5 (CMIP5), suggesting the contribution of internal variability to the intermodel uncertainty in ENSO amplitude change. However, the causations between changes in ENSO amplitude and the mean state are distinct between CESM-LE and CMIP5 ensemble. The CESM-LE results indicate that a large ensemble of ~15 members is needed to separate the relative contributions to ENSO amplitude change over the twenty-first century between forced response and internal variability."
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AbruptSLR

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Re: Modelling the Anthropocene
« Reply #151 on: August 31, 2017, 06:20:52 PM »
The linked reference uses a climate model to help quantify the impact of "Earth greening" on global warming & found that global land-surface warming was decreased by about 12% (over the past 30 years) due to this consideration.  This makes me wonder what will happen if/when "Earth greening" moves in the negative direction due to climate and land use stresses on vegetation:

Zhenzhong Zeng et. al. (2017), "Climate mitigation from vegetation biophysical feedbacks during the past three decades", Nature Climate Change  7, 432–436, doi:10.1038/nclimate3299

http://www.nature.com/nclimate/journal/v7/n6/full/nclimate3299.html?foxtrotcallback=true

Abstract: "The surface air temperature response to vegetation changes has been studied for the extreme case of land-cover change; yet, it has never been quantified for the slow but persistent increase in leaf area index (LAI) observed over the past 30 years (Earth greening). Here we isolate the fingerprint of increasing LAI on surface air temperature using a coupled land–atmosphere global climate model prescribed with satellite LAI observations. We find that the global greening has slowed down the rise in global land-surface air temperature by 0.09 ± 0.02 °C since 1982. This net cooling effect is the sum of cooling from increased evapotranspiration (70%), changed atmospheric circulation (44%), decreased shortwave transmissivity (21%), and warming from increased longwave air emissivity (−29%) and decreased albedo (−6%). The global cooling originated from the regions where LAI has increased, including boreal Eurasia, Europe, India, northwest Amazonia, and the Sahel. Increasing LAI did not, however, significantly change surface air temperature in eastern North America and East Asia, where the effects of large-scale atmospheric circulation changes mask local vegetation feedbacks. Overall, the sum of biophysical feedbacks related to the greening of the Earth mitigated 12% of global land-surface warming for the past 30 years."
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AbruptSLR

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Re: Modelling the Anthropocene
« Reply #152 on: September 12, 2017, 10:16:39 PM »
The linked comparison study provides insights into issues such as those raised by Sherwood et al (2014).  While the reference makes no definitive conclusions, it does highlight the importance of correctly modeling slow response feedback mechanisms associated with the ocean heat uptake (particularly in the (Equatorial Pacific) since 1750:

Kuan-Man Xu et al (9 September 2017), "Differences in the hydrological cycle and sensitivity between multiscale modeling frameworks with and without a higher-order turbulence closure", JAMES, DOI: 10.1002/2017MS000970

http://onlinelibrary.wiley.com/doi/10.1002/2017MS000970/full

Abstract: "Current conventional global climate models (GCMs) produce a weak increase in global-mean precipitation with anthropogenic warming in comparison with the lower tropospheric moisture increases. The motive of this study is to understand the differences in the hydrological sensitivity between two multiscale modeling frameworks (MMFs) that arise from the different treatments of turbulence and low clouds in order to aid to the understanding of the model spread among conventional GCMs. We compare the hydrological sensitivity and its energetic constraint from MMFs with (SPCAM-IPHOC) or without (SPCAM) an advanced higher-order turbulence closure. SPCAM-IPHOC simulates higher global hydrological sensitivity for the slow response but lower sensitivity for the fast response than SPCAM. Their differences are comparable to the spreads of conventional GCMs. The higher sensitivity in SPCAM-IPHOC is associated with the higher ratio of the changes in latent heating to those in net atmospheric radiative cooling, which is further related to a stronger decrease in the Bowen ratio with warming than in SPCAM. The higher sensitivity of cloud radiative cooling resulting from the lack of low clouds in SPCAM is another major factor in contributing to the lower precipitation sensitivity. The two MMFs differ greatly in the hydrological sensitivity over the tropical lands, where the simulated sensitivity of surface sensible heat fluxes to surface warming and CO2 increase in SPCAM-IPHOC is weaker than in SPCAM. The difference in divergences of dry static energy flux simulated by the two MMFs also contributes to the difference in land precipitation sensitivity between the two models."

Edit, see also:

Sherwood, S.C., Bony, S. and Dufresne, J.-L., (2014) "Spread in model climate sensitivity traced to atmospheric convective mixing", Nature; Volume: 505, pp 37–42, doi:10.1038/nature12829

http://www.nature.com/nature/journal/v505/n7481/full/nature12829.html

Fasullo, J.T. and Trenberth, K.E., (2012), "A Less Cloudy Future: The Role of Subtropical Subsidence in Climate Sensitivity", Science, vol. 338, pp. 792-794, 2012. http://dx.doi.org/10.1126/science.1227465.

http://www.sciencemag.org/content/338/6108/792
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AbruptSLR

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Re: Modelling the Anthropocene
« Reply #153 on: September 12, 2017, 10:44:09 PM »
The unusually high Pacific trade winds in recent decades is frequently associated with the faux hiatus; and the linked reference discusses bias in CMIP5 projections that resulted in under-predictions of the strength of these Pacific trade winds during the faux hiatus.

Jules B. Kajtar, Agus Santoso, Shayne McGregor, Matthew H. England & Zak Baillie (2017), "Model under-representation of decadal Pacific trade wind trends and its link to tropical Atlantic bias", Climate Dynamics", doi:10.1007/s00382-017-3699-5

https://link.springer.com/article/10.1007/s00382-017-3699-5

Abstract: "The strengthening of the Pacific trade winds in recent decades has been unmatched in the observational record stretching back to the early twentieth century. This wind strengthening has been connected with numerous climate-related phenomena, including accelerated sea-level rise in the western Pacific, alterations to Indo-Pacific ocean currents, increased ocean heat uptake, and a slow-down in the rate of global-mean surface warming. Here we show that models in the Coupled Model Intercomparison Project phase 5 underestimate the observed range of decadal trends in the Pacific trade winds, despite capturing the range in decadal sea surface temperature (SST) variability. Analysis of observational data suggests that tropical Atlantic SST contributes considerably to the Pacific trade wind trends, whereas the Atlantic feedback in coupled models is muted. Atmosphere-only simulations forced by observed SST are capable of recovering the time-variation and the magnitude of the trade wind trends. Hence, we explore whether it is the biases in the mean or in the anomalous SST patterns that are responsible for the under-representation in fully coupled models. Over interannual time-scales, we find that model biases in the patterns of Atlantic SST anomalies are the strongest source of error in the precipitation and atmospheric circulation response. In contrast, on decadal time-scales, the magnitude of the model biases in Atlantic mean SST are directly linked with the trade wind variability response."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

6roucho

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Re: Modelling the Anthropocene
« Reply #154 on: September 13, 2017, 08:14:04 PM »
AnruptSLR, how do you read so much and so widely? You're a machine!

AbruptSLR

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Re: Modelling the Anthropocene
« Reply #155 on: September 14, 2017, 04:22:32 PM »
AnruptSLR, how do you read so much and so widely? You're a machine!

As noted in the Adapting to the Anthropocene thread, by "... the recursive application of: deductive logic, inductive logic, the reduction of entropy, concentration/focus/effort/work and letting go of preconditioning ... "
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Modelling the Anthropocene
« Reply #156 on: September 19, 2017, 07:58:38 PM »
Given the complex nature of climate change, I think that CMIP6 and similarly future modeling efforts would do well to follow the advice given in the linked reference to combine "… dynamical modeling with data-driven methodological approaches (i.e., neural networks and Granger causality) …".

Fulvio Mazzocchi & Antonello Pasini (31 May 2017), "Climate model pluralism beyond dynamical ensembles", Wires: Climate Change, DOI: 10.1002/wcc.477

http://onlinelibrary.wiley.com/doi/10.1002/wcc.477/full

Abstract: "Using pluralist research strategies can be a profitable way to study complex systems. This contribution focuses on the approaches for studying the climate that make use of multiple different models, aiming to increase the reliability (in terms of robustness) of attribution results. This Opinion article argues that the traditional approach, which is based on ensemble runs of global climate models, only partially allows the application of a robustness scheme, owing to the difficulty to match or evaluate the conditions required for robustness (i.e., independence or heterogeneity among models). An alternative ‘multi-approach’ strategy is advanced, beyond dynamical modeling but still preserving the idea of model pluralism. Such a strategy, which uses a set of ensembles of different model types by combining dynamical modeling with data-driven methodological approaches (i.e., neural networks and Granger causality), seems to better match the condition of independence. In addition, neural networks and Granger causality lead to achievements in attribution studies that can complement those obtained by dynamical modeling."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Modelling the Anthropocene
« Reply #157 on: September 29, 2017, 03:40:48 PM »
The linked opinion piece describes actual and proposed systemic changes to CESM made in an effort to try to help modelers to gain a better understanding of the various Earth's Systems.  If this is done with sincerity it is a good idea; however, if managers/policy makers see that this affords them an opportunity to put their collective thumb on the modeling process/outcome then it is a bad idea:

Title: "When Less Is More: Opening the Door to Simpler Climate Models"

https://eos.org/opinions/when-less-is-more-opening-the-door-to-simpler-climate-models?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz092917

Extract: "Earth system models are resource intensive and complex. To cut through this complexity, the Community Earth System Model project will now be embracing a hierarchy of simpler climate models.

In a nutshell, ESMs may be good for simulating the climate system but may not be as valuable for understanding it. So we have now added a new set of tools within the Community Earth System Model (CESM) project: a hierarchy of simpler models to foster this understanding. Specifically, we are happy to announce that the next version of CESM will include two simple atmospheric models: a “dynamical core” and an “aquaplanet.”

We conclude by emphasizing one crucial point in Held’s proposal: Models in the hierarchy must be of lasting value. ESMs are constantly under development to promptly incorporate the latest findings or methods. However, we believe that at least some of the models in the hierarchy need to be forcefully shielded from the relentless cycle of model improving and updating. If those models are well chosen, their value will come precisely from the fact that they are not being updated. Because they remain unchanged, we will be able to understand them in great depth and thus close the gap between simulation and understanding—the ultimate motivation of this entire exercise."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Modelling the Anthropocene
« Reply #158 on: September 30, 2017, 06:23:48 PM »
The linked reference examines the output from CMIP5 projections to better differentiate between fast and slow components of the extratropical atmospheric circulation response to stepped radiative forcing.  I note that CMIP5 does not consider hosing from ice sheet mass loss & thus does not consider ice-climate feedback.  Nevertheless, the findings do indicate: (1) a fast response within 5 to 10 years of the stepped forcing; (2) an increase in ENSO activity (& increase in associated positive feedback mechanisms); and (3) an increase in Antarctic Amplification.  Hopefully, CMIP6 will consider freshwater hosing and ice-climate feedback.

Paulo Ceppi, Giuseppe Zappa, and Theodore G. Shepherd (28 September 2017), "Fast and slow components of the extratropical atmospheric circulation response to CO2 forcing", Journal of Climate, https://doi.org/10.1175/JCLI-D-17-0323.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0323.1?utm_content=buffer2cb5c&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Poleward shifts of the extratropical atmospheric circulation are a common response to CO2 forcing in global climate models (GCMs), but little is known about the time dependence of this response. Here it is shown that in coupled climate models, the long-term evolution of sea surface temperatures (SSTs) induces two distinct time scales of circulation response to step-like CO2 forcing. In most Coupled Model Intercomparison Project phase 5 GCMs as well as in the multi-model mean, all of the poleward shift of the midlatitude jets and Hadley cell edge occurs in a fast response within 5 to 10 years of the forcing, during which less than half of the expected equilibrium warming is realized. Compared with this fast response, the slow response over subsequent decades to centuries features stronger polar amplification (especially in the Antarctic), enhanced warming in the Southern Ocean, an El Niño-like pattern of tropical Pacific warming, and weaker land-sea contrast. Atmosphere-only GCM experiments demonstrate that the SST evolution drives the difference between the fast and slow circulation responses, although the direct radiative effect of CO2 also contributes to the fast response. It is further shown that the fast and slow responses determine the long-term evolution of the circulation response to warming in the RCP4.5 scenario. The results imply that shifts in midlatitude circulation generally scale with the radiative forcing, rather than with global-mean temperature change. A corollary is that time slices taken from a transient simulation at a given level of warming will considerably overestimate the extratropical circulation response in a stabilized climate."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Modelling the Anthropocene
« Reply #159 on: October 06, 2017, 06:49:20 PM »
The linked article recommends that future climate change projections should account for the effects of future volcanic eruptions, and I note that this should include the eruption of halogen emitting volcanoes in the WAIS:

Title: "5 links between erupting volcanoes and climate change"

https://www.eenews.net/stories/1060062893

Extract: "The effects of volcanoes need to be accounted for in future climate change predictions, according to a study published in August in Nature Climate Change. As researchers make future predictions from climate models, they need to factor in major eruptions over the next century, said Ed Hawkins, a climatologist at the University of Reading. To accurately forecast how climate change will transform the planet, researchers must account for temporary periods of cooling that come from volcanoes, according to Hawkins.

"Including some eruptions makes the changes in global temperature more variable, but as the effects of eruptions are only temporary they will not counteract the warming from greenhouse gases over the next century," he wrote in an email."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Modelling the Anthropocene
« Reply #160 on: October 06, 2017, 08:46:27 PM »
The former ACME project is now the Energy Exascale Earth System Model (E3SM) Project

Title: "Energy Exascale Earth System Model"

https://climatemodeling.science.energy.gov/projects/energy-exascale-earth-system-model

Extract: "The Energy Exascale Earth System Model (E3SM) project, previously known as ACME, is central to ESM as well as many of the Climate and Environmental Sciences Division activities, as it is developing a computationally advanced coupled climate-energy model to investigate the challenges posed by the interactions of weather-climate scale variability with energy and related sectors. The E3SM model simulates the fully coupled Earth system at high-resolution (15-25km, including higher resolution within regionally refined areas) and is incorporating coupling with energy, water, land-use and related energy-relevant activities, with a focus on near-term hind-casts (1970-2015) for model validation and a near-term projection (2015-2050) as needed for energy sector planning."
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AbruptSLR

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Re: Modelling the Anthropocene
« Reply #161 on: October 15, 2017, 06:00:03 PM »
While the linked reference's study of an Earth-like terra-planet may be of somewhat academic interest for newly discovered planets, the authors do note its possible relevance to an imaginary drop from present day conditions to the Snowball Earth state:

Kalidindi, S., Reick, C. H., Raddatz, T., and Claussen, M.: Two drastically different climate states on an Earth-like terra-planet, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2017-84, in review, 2017.

https://www.earth-syst-dynam-discuss.net/esd-2017-84/

Abstract. We study an Earth-like terra-planet with an overland recycling mechanism bringing fresh water back from higher latitudes to the lower latitudes. By performing model simulations for such a planet we find two drastically different climate states for the same set of boundary conditions and parameter values: A Cold and Wet (CW) state (present-day Earth-like climate) with dominant low-latitude precipitation and, a Hot and Dry (HD) state with only high-latitude precipitation. We notice that for perpetual equinox conditions, both climate states are stable below a certain threshold value of background soil albedo while above the threshold only the CW state is stable. Starting from the HD state and increasing background soil albedo above the threshold causes an abrupt shift from the HD state to the CW state resulting in a sudden cooling of about 35 °C globally which is of the order of the temperature difference between the present-day and the Snowball Earth state. In contrast to the Snowball Earth instability, we find that the sudden cooling in our study is driven by the cloud albedo feedback rather than the snow-albedo feedback. Also, when albedo in the CW state is reduced back to zero the terra-planet does not display a closed hysteresis. This is due to the high cloud cover in the CW state hiding the surface from solar irradiation. As a result, this reduction of background surface albedo has only a minor effect on the top of the atmosphere radiation balance, thereby making it impossible to heat the planet sufficiently strongly to switch back to the HD state. Additional simulations point to a similar abrupt transition from HD state to the CW state for non-zero obliquity which is the only stable state in this configuration. Our study also has implications for the habitability of Earth-like terra-planets. At the inner edge of the habitable zone, the higher cloud cover in the CW state cools the planet and may prevent the onset of a runaway greenhouse state. At the outer edge, the resupply of water at lower latitudes stabilizes the greenhouse effect and keeps the planet in the HD state and may prevent water from getting trapped at higher latitudes in frozen form. Overall, the existence of bi-stability in the presence of an overland recycling mechanism hints at the possibility of a wider habitable zone for Earth-like terra-planets at lower obliquities.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Modelling the Anthropocene
« Reply #162 on: October 16, 2017, 01:32:36 AM »
The linked reference discusses a climate model of intermediate sophistication that represents an initial effort to model Earth Systems subject to changing from on climate state to another due to periodic climate attractors:

Valerio Lucarini and Tamás Bódai (2017), "Edge states in the climate system: exploring global instabilities and critical transitions", Nonlinearity 30 R32, https://doi.org/10.1088/1361-6544/aa6b11

http://iopscience.iop.org/article/10.1088/1361-6544/aa6b11/meta

Abstract: "Multistability is a ubiquitous feature in systems of geophysical relevance and provides key challenges for our ability to predict a system's response to perturbations. Near critical transitions small causes can lead to large effects and—for all practical purposes—irreversible changes in the properties of the system. As is well known, the Earth climate is multistable: present astronomical and astrophysical conditions support two stable regimes, the warm climate we live in, and a snowball climate characterized by global glaciation. We first provide an overview of methods and ideas relevant for studying the climate response to forcings and focus on the properties of critical transitions in the context of both stochastic and deterministic dynamics, and assess strengths and weaknesses of simplified approaches to the problem. Following an idea developed by Eckhardt and collaborators for the investigation of multistable turbulent fluid dynamical systems, we study the global instability giving rise to the snowball/warm multistability in the climate system by identifying the climatic edge state, a saddle embedded in the boundary between the two basins of attraction of the stable climates. The edge state attracts initial conditions belonging to such a boundary and, while being defined by the deterministic dynamics, is the gate facilitating noise-induced transitions between competing attractors. We use a simplified yet Earth-like intermediate complexity climate model constructed by coupling a primitive equations model of the atmosphere with a simple diffusive ocean. We refer to the climatic edge states as Melancholia states and provide an extensive analysis of their features. We study their dynamics, their symmetry properties, and we follow a complex set of bifurcations. We find situations where the Melancholia state has chaotic dynamics. In these cases, we have that the basin boundary between the two basins of attraction is a strange geometric set with a nearly zero codimension, and relate this feature to the time scale separation between instabilities occurring on weather and climatic time scales. We also discover a new stable climatic state that is similar to a Melancholia state and is characterized by non-trivial symmetry properties."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Adam Ash

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Re: Modelling the Anthropocene
« Reply #163 on: October 26, 2017, 09:43:29 PM »

Burial-induced oxygen-isotope re-equilibration of fossil foraminifera explains ocean paleotemperature paradoxes
https://www.nature.com/articles/s41467-017-01225-9

According to the current methodology, the temperature of the ocean depths, and the surface of the polar ocean, was some 15C (59F) higher 100 million years ago, compared to now.

These estimates have been challenged, however, by a joint team of researchers from the French National Center for Scientific Research (CNRS) and the Swiss Federal Institute of Technology in Lausanne (EPFL).

In their study, published in Nature Communications, the team posits that ocean temperatures may have remained relatively stable throughout this period, raising serious concerns about the current level of climate change being experienced by Mother Earth.

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Re: Modelling the Anthropocene
« Reply #164 on: October 27, 2017, 12:01:01 AM »
If that Bernard paper holds up, it answers the question as to why the polar oceans in Cretaceous and Paleogene were so much warmer. The answer is that they were not, and the equator to pole gradient was larger than supposed.

"Furthermore, the present study suggests that the vertical and latitudinal temperature gradients of the late Cretaceous and Paleogene oceans were likely not very different from the current ones."

Fig 4 tells the story. I attach.

sidd

AbruptSLR

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Re: Modelling the Anthropocene
« Reply #165 on: October 27, 2017, 03:13:24 PM »
Tropical-Extratropical telecommunications (particularly w.r.t. ENSO patterns) are of fundamental importance for understanding numerous feedback mechanisms including Arctic Amplification and Hansen's ice-climate feedback (especially w.r.t. WAIS stability):

Cristiana Stan, David M. Straus, Jorgen S. Frederiksen, Hai Lin, Eric D. Maloney & Courtney Schumacher
 (24 October 2017), "Review of Tropical-Extratropical Teleconnections on Intraseasonal Time Scales", Review of Geophysics, DOI: 10.1002/2016RG000538

http://onlinelibrary.wiley.com/doi/10.1002/2016RG000538/abstract

Abstract: "The interactions and teleconnections between the tropical and midlatitude regions on intraseasonal time scales are an important modulator of tropical and extratropical circulation anomalies and their associated weather patterns. These interactions arise due to the impact of the tropics on the extratropics, the impact of the midlatitudes on the tropics, and two-way interactions between the regions. Observational evidence, as well as theoretical studies with models of complexity ranging from the linear barotropic framework to intricate Earth system models, suggest the involvement of a myriad of processes and mechanisms in generating and maintaining these interconnections. At this stage, our understanding of these teleconnections is primarily a collection of concepts; a comprehensive theoretical framework has yet to be established. These intraseasonal teleconnections are increasingly recognized as an untapped source of potential subseasonal predictability. However, the complexity and diversity of mechanisms associated with these teleconnections, along with the lack of a conceptual framework to relate them, prevent this potential predictability from being translated into realized forecast skill. This review synthesizes our progress in understanding the observed characteristics of intraseasonal tropical-extratropical interactions and their associated mechanisms, identifies the significant gaps in this understanding, and recommends new research endeavors to address the remaining challenges."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Modelling the Anthropocene
« Reply #166 on: October 27, 2017, 04:57:53 PM »
The linked article indicates that in order to more accurately model the Atlantic Meridional Mode, cloud feedback needs to be positive:

Myers, T.A., Mechoso, C.R. & DeFlorio, M.J. (2017), "Importance of positive cloud feedback for tropical Atlantic interhemispheric climate variability", Clim Dy., https://doi.org/10.1007/s00382-017-3978-1

https://link.springer.com/article/10.1007%2Fs00382-017-3978-1?utm_content=buffer90766&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Over the tropical Atlantic during boreal spring, average interhemispheric differences in sea-surface temperature (SST) coincide with a coherent pattern of interannual climate variability often referred to as the Atlantic Meridional Mode. This includes anomalous SST and sea-level pressure roughly anti-symmetric about the equator, as well as cross-equatorial near-surface winds directed toward the warmer hemisphere. Within subtropical marine boundary layer cloud regions in both hemispheres, enhanced cloudiness associated with this variability is co-located with cool SST, a strong temperature inversion, and cold horizontal surface temperature advection, while reduced cloudiness is associated with the opposite meteorological conditions. This is indicative a positive cloud feedback that reinforces the underlying SST anomalies. The simulation of this feedback varies widely among models participating in phase 5 of the Coupled Model Intercomparison Project. Models that fail to simulate this feedback substantially underestimate the amplitudes of typical tropical Atlantic interhemispheric variability in cloudiness off of the equator, SST, and atmospheric circulation. Models that correctly reproduce a positive cloud feedback generally produce higher and more realistic amplitudes of variability, but with substantial scatter. Marine boundary layer clouds therefore appear to be a key element of springtime coupled atmosphere–ocean variability over the tropical Atlantic. A markedly more successful simulation of this variability in climate models may be obtained by better representing boundary layer cloud processes."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Modelling the Anthropocene
« Reply #167 on: October 27, 2017, 05:46:28 PM »
If that Bernard paper holds up, it answers the question as to why the polar oceans in Cretaceous and Paleogene were so much warmer. The answer is that they were not, and the equator to pole gradient was larger than supposed.

I think that the key take away message here is that current climate models have likely been calibrated to over predict the amount of heat energy that the oceans will absorb with continuing radiative forcing; which will leave more heat in the atmosphere resulting in more rapid increases in GMSTA (global mean surface temperature anomalies), which implies that ECS is likely towards the upper end of model projections.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Modelling the Anthropocene
« Reply #168 on: October 30, 2017, 03:19:01 PM »
If you want a model to indicate that you will succeed, all you have to do is to jack around with your assumption/input; and then claim plausible deniability when your projects don't match the future reality. 

Title: "Guest post: Who will deliver the negative emissions needed to avoid 2C warming?"

https://www.carbonbrief.org/guest-post-who-will-deliver-the-negative-emissions-needed-to-avoid-2c-warming

Extract: "“Negative emissions”, also known as “carbon dioxide removal” (CDR), refers to a group of approaches and technologies that take CO2 from the atmosphere and store it on land, underground or in the oceans.

Integrated Assessment Models (IAMs) also indicate that it is cheaper to have large-scale CDR in the future, than to have deeper mitigation now.

Love it or hate it, it may be that CDR is simply unavoidable if society wants to stabilise temperatures. If one can accept that we need CDR, the real debate becomes at what scale.

The land areas required for such large-scale CDR would be the size of India, or even larger."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Modelling the Anthropocene
« Reply #169 on: October 30, 2017, 07:21:01 PM »
The linked open access reference discusses improvements to modeling global soil carbon:

Kefeng Wang, Changhui Peng, Qiuan Zhu, Xiaolu Zhou, Meng Wang, Kerou Zhang & Gangsheng Wang (27 October 2017), "Modeling Global Soil Carbon and Soil Microbial Carbon by Integrating Microbial Processes into the Ecosystem Process Model TRIPLEX-GHG", JAMES, DOI: 10.1002/2017MS000920 

http://onlinelibrary.wiley.com/doi/10.1002/2017MS000920/full

Abstract: "Microbial physiology plays a critical role in the biogeochemical cycles of the Earth system. However, most traditional soil carbon models are lacking in terms of the representation of key microbial processes that control the soil carbon response to global climate change. In this study, the improved process-based model TRIPLEX-GHG was developed by coupling it with the new MEND (Microbial-ENzyme-mediated Decomposition) model to estimate total global soil organic carbon (SOC) and global soil microbial carbon. The new model (TRIPLEX-MICROBE) shows considerable improvement over the previous version (TRIPLEX-GHG) in simulating SOC. We estimated the global soil carbon stock to be approximately 1195 Pg C, with 348 Pg C located in the high northern latitudes, which is in good agreement with the well-regarded Harmonized World Soil Database (HWSD) and the Northern Circumpolar Soil Carbon Database (NCSCD). We also estimated the global soil microbial carbon to be 21 Pg C, similar to the 23 Pg C estimated by Xu et al. (2014). We found that the microbial carbon quantity in the latitudinal direction showed reversions at approximately 30°N, near the equator and at 25°S. A sensitivity analysis suggested that the tundra ecosystem exhibited the highest sensitivity to a 1°C increase or decrease in temperature in terms of dissolved organic carbon (DOC), microbial biomass carbon (MBC), and mineral-associated organic carbon (MOC). However, our work represents the first step toward a new generation of ecosystem process models capable of integrating key microbial processes into soil carbon cycles."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Modelling the Anthropocene
« Reply #170 on: November 12, 2017, 01:01:03 AM »
The linked reference uses a ESM to study the impacts of freshwater hosing from the Greenland Ice Sheet.  While this is valuable information, studying the impacts of abrupt freshwater hosing from the WAIS would be even more useful:

Haijun Yang, Qin Wen, Jie Yao & Yuxing Wang (2017), "Bjerknes Compensation in Meridional Heat Transport under Freshwater Forcing and the Role of Climate Feedback", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0824.1

http://journals.ametsoc.org/doi/full/10.1175/JCLI-D-16-0824.1

Abstract: "Using a coupled Earth climate model, freshwater forcing experiments are performed to study the Bjerknes compensation (BJC) between meridional atmosphere heat transport (AHT) and meridional ocean heat transport (OHT). Freshwater hosing in the North Atlantic weakens the Atlantic meridional overturning circulation (AMOC) and thus reduces the northward OHT in the Atlantic significantly, leading to a cooling (warming) in the surface layer in the Northern (Southern) Hemisphere. This results in an enhanced Hadley cell and northward AHT. Meanwhile, the OHT in the Indo-Pacific is increased in response to the Hadley cell change, partially offsetting the reduced OHT in the Atlantic. Two compensations occur here: compensation between the AHT and the Atlantic OHT, and that between the Indo-Pacific OHT and the Atlantic OHT. The AHT change undercompensates the OHT change by about 60% in the extratropics, while the former overcompensates the latter by about 30% in the tropics due to the Indo-Pacific change. The BJC can be understood from the viewpoint of large-scale circulation change. However, the intrinsic mechanism of BJC is related to the climate feedback of the Earth system. The authors’ coupled model experiments confirm that the occurrence of BJC is an intrinsic requirement of local energy balance, and local climate feedback determines the extent of BJC, consistent with previous theoretical results. Even during the transient period of climate change, the BJC is well established when the ocean heat storage is slowly varying and its change is much weaker than the net local heat flux change at the ocean surface. The BJC can be deduced from the local climate feedback. Under the freshwater forcing, the overcompensation in the tropics is mainly caused by the positive longwave feedback related to clouds, and the undercompensation in the extratropics is due to the negative longwave feedback related to surface temperature change. Different dominant feedbacks determine different BJC scenarios in different regions, which are in essence constrained by local energy balance."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson