Conservative Scientists & its Consequences

[Daniel B.]

Hence, the big debate about which is more accurate; modeled values, which are biased high, or observational values, which are biased low?

As ECS changes depending on Earth System conditions and on rate and magnitude of radiative, AR5's compilation of different measures of ECS (see attached image) is actually comparing apples to oranges when comparing inferred ECS values from instrumentation, paleodata, climatological constraints and Earth System models.  This image makes it clear that inferred values of ECS based on instruments can be as high as 9C, while the mean value for ECS determined by ACME of 5.2C is not even included in AR5's compilation.  As the following extract makes clear, the value of ECS that policy makers should be interested in is the one that will match the Earth Systems and radiative forcing pattern for the next several coming centuries, and that inferred measures of past ECS values should primarily be used for calibrating state-of-the-art ESMs like E3SM.

Title: "IPCC AR5 Climate Sensitivity “A consensus of Controversies”"

http://www.gci.org.uk/images/IPCC_AR5_CS.pdf

Extract: "No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies.
…
The equilibrium climate sensitivity quantifies the response of the climate system to constant radiative forcing on multi-century time scales. It is defined as the change in global mean surface temperature at equilibrium that is caused by a doubling of the atmospheric CO2 concentration."

See also:

https://en.wikipedia.org/wiki/Global_Commons_Institute

Yes, there exists a wide range of values, from about 0.5 up to 9.  Unfortunately, there is no agreement as to which method(s) generate the best values.  Therefore, anyone trying to make predictions too far into the future are simply guessing.

[Shared Humanity]

Yes, there exists a wide range of values, from about 0.5 up to 9.  Unfortunately, there is no agreement as to which method(s) generate the best values.  Therefore, anyone trying to make predictions too far into the future are simply guessing.

I can't even guess tomorrow's temperature right. We should wait for a couple of decades and see how things work out.

[Daniel B.]

Yes, there exists a wide range of values, from about 0.5 up to 9.  Unfortunately, there is no agreement as to which method(s) generate the best values.  Therefore, anyone trying to make predictions too far into the future are simply guessing.

I can't even guess tomorrow's temperature right. We should wait for a couple of decades and see how things work out.

By then, we may have a more accurate calculation of the ECS - or if it is even constant (unlikely).

[Shared Humanity]

Yes, there exists a wide range of values, from about 0.5 up to 9.  Unfortunately, there is no agreement as to which method(s) generate the best values.  Therefore, anyone trying to make predictions too far into the future are simply guessing.

I can't even guess tomorrow's temperature right. We should wait for a couple of decades and see how things work out.

By then, we may have a more accurate calculation of the ECS - or if it is even constant (unlikely).

Having 2 more decades of hard data will certainly provide us with far better estimates of ECS with narrower confidence intervals. Of course, since we're heading towards a climate disaster and the possibility of higher ECS is very real with its serious implications for life on the planet, I think it is ill advised to wait.

But then, you already know that.

[AbruptSLR]

The linked research identifies why current climate models have underestimated the decadal variability of Pacific Ocean.  As this variability is directly tied to ENSO variability, and as climate variability is directly tied to the magnitude of ECS; it is clear (to me) that when current models (hopefully including CMIP6 models) are correct to minimize their current bias in this matter, they will project higher values of ECS than projected by AR5:

Title: "Research sheds new light on understanding Pacific Trade Winds"

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

Extract: "Now a new international study, featuring Professor Mat Collins from the University of Exeter, has for the first time been able to identify a deficiency thought to underpin this model underrepresentation of Pacific Trade Wind trends.
…
Lead study author Dr. Shayne McGregor, from the Monash School of Earth, Atmosphere and Environment added: "Numerical models are known to have biases in their representation of the long term average climate, these same models are also known to have biases in their representation of variability, which includes the underrepresentation of decadal variability in the Pacific Ocean.

"However, these two issues have often been treated separately as there was little evidence linking the two until now. Our results identify biases in the representation of the model long term average appear to play a prominent role in the under representation of this recent Pacific Ocean trade wind strengthening."

Since all of the ocean basins are connected by the atmosphere and ocean, it is not just the mean state in the Pacific Ocean that is important, according to Dr. McGregor."

See also:

McGregor et al. (2018), "Model tropical Atlantic biases underpin diminished Pacific decadal variability", Nature Climate Change, doi:10.1038/s41558-018-0163-4

http://www.nature.com/articles/s41558-018-0163-4

[AbruptSLR]

While the reported implications of the three newly identified bed troughs at the bottleneck between East & West Antarctica (i.e. a projection of greater ice mass loss from the interior of Antarctica with continued global warming) are bad enough; I note that the fact that these troughs exist is a clear indication that such higher ice mass loss from the interior of Antarctica has occurred in the past.  This consideration increases the likelihood of such rapid ice mass loss events occurring, and of hydraulically connecting the Weddell Sea to the Ross Sea, later this century:

Kate Winter et al. (2018), "Topographic Steering of Enhanced Ice Flow at the Bottleneck Between East and West Antarctica", Geophysical Research Letters, doi:10.1029/2018GL077504

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018GL077504

Abstract: "Hypothesized drawdown of the East Antarctic Ice Sheet through the “bottleneck” zone between East and West Antarctica would have significant impacts for a large proportion of the Antarctic Ice Sheet. Earth observation satellite orbits and a sparseness of radio echo sounding data have restricted investigations of basal boundary controls on ice flow in this region until now. New airborne radio echo sounding surveys reveal complex topography of high relief beneath the southernmost Weddell/Ross ice divide, with three subglacial troughs connecting interior Antarctica to the Foundation and Patuxent Ice Streams and Siple Coast ice streams. These troughs route enhanced ice flow through the interior of Antarctica but limit potential drawdown of the East Antarctic Ice Sheet through the bottleneck zone. In a thinning or retreating scenario, these topographically controlled corridors of enhanced flow could however drive ice divide migration and increase mass discharge from interior West Antarctica to the Southern Ocean."

Plain Language Summary: "The East and West Antarctic Ice Sheets meet at the inland termination of the Transantarctic Mountains. The ice sheets coalesce at a major ice divide, which could migrate and impact ice flow across large parts of Antarctica. A lack of satellite observations of ice flow and ice thickness has previously restricted characterization of this region, its glaciology, and its subglacial landscape. Our ice-penetrating radar surveys reveal three deep subglacial valleys and mountainous subglacial topography beneath the ice divide. New measurements of ice flow evidence faster ice flow within these troughs than in the surrounding thinner ice. Were the ice sheet to shrink in size, an increase in the speed at which ice flows through these troughs could lead to the ice divide moving and increase the rate at which ice flows out from the center of Antarctica to its edges."

See also:

Title: "Giant canyons discovered in Antarctica"

http://www.bbc.com/news/science-environment-44245893

Extract: "Scientists have discovered three vast canyons in one of the last places to be explored on Earth - under the ice at the South Pole.
…
And if Antarctica thins in a warming climate, as scientists suspect it will, then these channels could accelerate mass towards the ocean, further raising sea-levels.

"These troughs channelise ice from the centre of the continent, taking it towards the coast," explained Dr Winter.

"Therefore, if climate conditions change in Antarctica, we might expect the ice in these troughs to flow a lot faster towards the sea. That makes them really important, and we simply didn't know they existed before now," she told BBC News.

[AbruptSLR]

The simple fact of the matter is that as the AMOC continues to slow down, Hansen's ice-climate feedback mechanism will become increasingly more positive (and I note that this consideration is not addressed in AR5 projections):

Title: "If you doubt that the AMOC has weakened, read this"

http://www.realclimate.org/index.php/archives/2018/05/if-you-doubt-that-the-amoc-has-weakened-read-this/#more-21423

[AbruptSLR]

1 would like to reiterate Paul Edwards' 2011 message to climate change skeptics: "without models, there are no data."  This is obvious with regards to satellite 'observations' related to cloud feedback where extensive uncertainties associated with assumptions and calculations are involved before researchers publish any 'data', and this is particularly important regarding the various types of ECS reported by various researchers:

Title: "A Vast Machine - Computer Models, Climate Data, and the Politics of Global Warming"

https://mitpress.mit.edu/books/vast-machine

Extract: "Global warming skeptics often fall back on the argument that the scientific case for global warming is all model predictions, nothing but simulation; they warn us that we need to wait for real data, “sound science.” In A Vast Machine Paul Edwards has news for these skeptics: without models, there are no data."

[Daniel B.]

1 would like to reiterate Paul Edwards' 2011 message to climate change skeptics: "without models, there are no data."  This is obvious with regards to satellite 'observations' related to cloud feedback where extensive uncertainties associated with assumptions and calculations are involved before researchers publish any 'data', and this is particularly important regarding the various types of ECS reported by various researchers:

Title: "A Vast Machine - Computer Models, Climate Data, and the Politics of Global Warming"

https://mitpress.mit.edu/books/vast-machine

Extract: "Global warming skeptics often fall back on the argument that the scientific case for global warming is all model predictions, nothing but simulation; they warn us that we need to wait for real data, “sound science.” In A Vast Machine Paul Edwards has news for these skeptics: without models, there are no data."

Does that mean that he is agreeing that only modeled predictions exist?

[AbruptSLR]

1 would like to reiterate Paul Edwards' 2011 message to climate change skeptics: "without models, there are no data."  This is obvious with regards to satellite 'observations' related to cloud feedback where extensive uncertainties associated with assumptions and calculations are involved before researchers publish any 'data', and this is particularly important regarding the various types of ECS reported by various researchers:

Title: "A Vast Machine - Computer Models, Climate Data, and the Politics of Global Warming"

https://mitpress.mit.edu/books/vast-machine

Extract: "Global warming skeptics often fall back on the argument that the scientific case for global warming is all model predictions, nothing but simulation; they warn us that we need to wait for real data, “sound science.” In A Vast Machine Paul Edwards has news for these skeptics: without models, there are no data."

Does that mean that he is agreeing that only modeled predictions exist?

In a constantly changing world, reality is as much a function of the trend as of one's last observation:

Kate Marvel, Robert Pincus, Gavin A. Schmidt & Ron L. Miller (29 January 2018), "Internal Variability and Disequilibrium Confound Estimates of Climate Sensitivity From Observations", Geophysical Research Letters, https://doi.org/10.1002/2017GL076468

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076468

Extract: "An emerging literature suggests that estimates of equilibrium climate sensitivity (ECS) derived from recent observations and energy balance models are biased low because models project more positive climate feedback in the far future. Here we use simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to show that across models, ECS inferred from the recent historical period (1979–2005) is indeed almost uniformly lower than that inferred from simulations subject to abrupt increases in CO2 radiative forcing. However, ECS inferred from simulations in which sea surface temperatures are prescribed according to observations is lower still. ECS inferred from simulations with prescribed sea surface temperatures is strongly linked to changes to tropical marine low clouds. However, feedbacks from these clouds are a weak constraint on long‐term model ECS. One interpretation is that observations of recent climate changes constitute a poor direct proxy for long‐term sensitivity."

[jai mitchell]

ECS inferred from simulations with prescribed sea surface temperatures is strongly linked to changes to tropical marine low clouds. However, feedbacks from these clouds are a weak constraint on long‐term model ECS.

Funny, that isn't the result of the most comprehensive analysis of modeled constraints today.  The tropical cloud feedback is considered to be one of the most robust in this analysis.

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0631.1

Emergent constraints are quantities that are observable from current measurements and have skill predicting future climate. This study explores 19 previously proposed emergent constraints related to equilibrium climate sensitivity (ECS; the global-average equilibrium surface temperature response to CO2 doubling). Several constraints are shown to be closely related, emphasizing the importance for careful understanding of proposed constraints. A new method is presented for decomposing correlation between an emergent constraint and ECS into terms related to physical processes and geographical regions. Using this decomposition, one can determine whether the processes and regions explaining correlation with ECS correspond to the physical explanation offered for the constraint. Shortwave cloud feedback is generally found to be the dominant contributor to correlations with ECS because it is the largest source of intermodel spread in ECS. In all cases, correlation results from interaction between a variety of terms, reflecting the complex nature of ECS and the fact that feedback terms and forcing are themselves correlated with each other. For 4 of the 19 constraints, the originally proposed explanation for correlation is borne out by our analysis. These four constraints all predict relatively high climate sensitivity. The credibility of six other constraints is called into question owing to correlation with ECS coming mainly from unexpected sources and/or lack of robustness to changes in ensembles. Another six constraints lack a testable explanation and hence cannot be confirmed. The fact that this study casts doubt upon more constraints than it confirms highlights the need for caution when identifying emergent constraints from small ensembles.

[AbruptSLR]

Aside from the ecological implications of the newly identified marine paths for Pacific plankton to follow thru the Arctic and into the Atlantic (see the attached image), this article does not address such potential cascading positive radiative forcing feedback mechanisms as:

1. More Arctic plankton decreases Arctic albedo in a warming Arctic with thinning sea ice;
 
2. If/when the Beaufort Gyre releases a large pulse of relatively fresh water into the North Atlantic this would accelerate Arctic Amplification; and

3. If/when the WAIS collapses, the rate of Pacific seawater into the Arctic would increase abruptly and would also contribute to a cascading acceleration of Arctic Amplification (and associated global warming).

Title: "New Paths for Plankton in Warming Arctic?"

https://eos.org/articles/new-paths-for-plankton-in-warming-arctic?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz060118

Extract: "Water flowing from the Pacific to the Atlantic could find new shortcuts, enabling plankton to survive the trip through the cold polar region."

[AbruptSLR]

Contrary to current climate consensus conventional wisdom, new finding indicate that as the oceans continue to warm the less the oceans will be able to act as a carbon sink for atmospheric CO₂.  This means that the concentration of atmospheric CO₂ will increase faster than previously expected:

Title: "Invisible scum on sea cuts CO2 exchange with air 'by up to 50%'"

https://www.theguardian.com/environment/2018/may/28/invisible-scum-on-sea-cuts-co2-exchange-with-air-by-up-to-50

Extract: "The world’s oceans absorb around a quarter of all man-made carbon dioxide emissions, making them the largest long-term sink of carbon on Earth.
…
They found surfactants can reduce carbon dioxide exchange by up to 50%.
…
Dr Ryan Pereira, a Lyell research fellow at Heriot-Watt University in Edinburgh, said: “As surface temperatures rise, so too do surfactants, which is why this is such a critical finding.
“The warmer the ocean surface gets, the more surfactants we can expect, and an even greater reduction in gas exchange.
…
Rob Upstill-Goddard, professor of marine biogeochemistry at Newcastle University, said: “These latest results build on our previous findings that, contrary to conventional wisdom, large sea surface enrichments of natural surfactants counter the effects of high winds.”"

[AbruptSLR]

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."

[jai mitchell]

Cross Posted from Aerosols thread.

------------
Earlier papers that project aerosol forcing have real problems since many (most!) of the ESM models did not include key (known) atmospheric and atmospheric chemistry interactions with aerosols.  These models underestimate the aerosol effect.  This has been well known even before the publication of AR5 as satellite observations indicated much greater effects than were being modeled.

This total indirect effect is comprised of First (FIE) and Second (SIE) indirect effects, both are negative (cooling). 

The lack of these mechanisms in some models and the poor representation (compared to direct observations in others) led to the great uncertainty bars in the AR4 and AR5 (image below) for this effect.  The total indirect effect here is labeled "Cloud Adjustments due to Aerosols" with a median value of about 0.56 Watts/m^2.

Recent observations from the Satellite record indicate that the FIE component itself is underestimated by approximately 23% which has a cascading local effect based on relative humidity of several watts per meter squared.  See: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL077679

One‐unit enhancement in aerosol scattering coefficient by swelling effect is found to lead to a systematic underestimation of the first indirect effect (FIE) by about 23% that can result in an underestimation in the FIE‐related radiative forcing by several W/m2 depending on aerosol properties and relative humidity.

Recent observations from the satellite record performed by a different team of scientists shows that the FIE effect is approximately double the total effect shown in the graphic below (and cited as the median value of aerosol cloud impacts in AR5) See : http://www-k12.atmos.washington.edu/~dennis/McCoy-2017-Theglobalaerosol-cloud.pdf

Using preindustrial emissions models, the change in Nd between preindustrial and present day is estimated. Nd is inferred to have more than tripled in some regions. Cloud properties from Moderate Resolution Imaging Spectroradiometer (MODIS) are used to estimate the radiative forcing due to this change in Nd. The Twomey (FIE) effect operating in isolation is estimated to create a radiative forcing of -0.97 ± 0.23 W m^2 relative to the preindustrial era.

The problem (and this will be cross posted in the "Conservative Scientists" thread) is that these more recent papers that rely on models specifically tuned to include the total effects of aerosols show much higher cooling impacts, especially in the  Arctic than your examples.  see: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076079

We note that in two models, Arctic warming due to aerosol reductions reaches 4°C in some locations (Figures S2–S5). The four‐model mean increase for the 60°N–90°N region is 2.8°C.

note:  Even the four models used in this paper severely underestimate the FIE as shown in the first papers (23%) cited which was published only 1 month ago

Image of average model (4 model) response to aerosols removal found here: https://wol-prod-cdn.literatumonline.com/cms/attachment/46814f2f-f617-4dea-83ce-0ab4c61244bf/grl56865-fig-0002-m.jpg

You can download the Supplementary information with the individual model results of aerosol removal on temperatures (figures S2-S5) here:
https://agupubs.onlinelibrary.wiley.com/action/downloadSupplement?doi=10.1002%2F2017GL076079&attachmentId=2186427861

It is strongly urged that you limit your research for best accuracy to papers less than 2 years old since the modeling capabilities have increased significantly since 2015.  I understand that this has produced a lot of confusion in the discussion since the understanding of these aerosol impacts are changing very rapidly.

[AbruptSLR]

I look forward to when the following reference is published, but based on the title it appears to indicate that paleo-based estimates of ECS are higher when they account for changing temperature patterns:

Andrews T, JM Gregory, D Paynter, LG Silvers, C Zhou, T Mauritsen, MJ Webb, KC Armour, PM Forster and H Titchner (2018) Accounting for changing temperature patterns increases historical estimates of climate sensitivity (submitted for publication)

[AbruptSLR]

New research indicates that the Southern Ocean is absorbing less CO₂ than previously assumed, possibly due changes in the surface currents associate with changes in the westerlies.

Title: "Antarctic Ocean Discovery Warns of Faster Global Warming"

http://www.climatecentral.org/news/antarctic-ocean-discovery-warns-of-faster-global-warming-21865

Extract: "A group of scientists, including one from the University of Arizona, has new findings suggesting Antarctica's Southern Ocean — long known to play an integral role in climate change — may not be absorbing as much pollution as previously thought.

The old belief was the ocean pulled about 13 percent of the world’s carbon dioxide — a greenhouse gas that contributes to climate change — out of the atmosphere, helping put the brakes on rising global temperatures.

To reach their contradictory conclusion, the team used state-of-the-art sensors to collect more data on the Southern Ocean than ever before, including during the perilous winter months that previously made the research difficult if not impossible.

Some oceanographers suspect that less CO2 is being absorbed because the westerlies — the winds that ring the southernmost continent — are tightening like a noose. As these powerful winds get more concentrated, they dig at the water, pushing it out and away."

[AbruptSLR]

The linked reference uses an updated version of the World3 model called the World Energy Model (WEM) to reassess limits to growth.  WEM projects a reduced sensitivity to socio-economic collapse, but it adopts consensus climate change dogma to project only a 2.4 to 2.7C increase in mean global warming by 2100.  If the authors had assumed an ECS value of 5.2C as projected by the ACME climate model I believe that they might have projected a socio-economic collapse in the 2050 to 2060 timeframe:

Thomas Ansell & Steve Cayzer (September 2018), "Limits to growth redux: A system dynamics model for assessing energy and climate change constraints to global growth", Energy Policy, Volume 120, Pages 514-525, https://doi.org/10.1016/j.enpol.2018.05.053

https://www.sciencedirect.com/science/article/pii/S0301421518303562

Abstract: "This study investigates the notion of limits to socioeconomic growth with a specific focus on the role of climate change and the declining quality of fossil fuel reserves. A new system dynamics model has been created. The World Energy Model (WEM) is based on the World3 model (The Limits to Growth, Meadows et al., 2004) with climate change and energy production replacing generic pollution and resources factors. WEM also tracks global population, food production and industrial output out to the year 2100. This paper presents a series of WEM's projections; each of which represent broad sweeps of what the future may bring. All scenarios project that global industrial output will continue growing until 2100. Scenarios based on current energy trends lead to a 50% increase in the average cost of energy production and 2.4–2.7 °C of global warming by 2100. WEM projects that limiting global warming to 2 °C will reduce the industrial output growth rate by 0.1–0.2%. However, WEM also plots industrial decline by 2150 for cases of uncontrolled climate change or increased population growth. The general behaviour of WEM is far more stable than World3 but its results still support the call for a managed decline in society's ecological footprint."

[AbruptSLR]

Remember that ice mass loss from Antarctica is expected to accelerate nonlinearly with continued global warming, so while the current Antarctic contribution to sea level rise of 0.5mm/y may seem small, when it is increased nonlinearly to 2100, this small value could become big:

Title: "Antarctica’s Ice Sheet Is Melting Three Times Faster Than We Thought"

https://www.thedailybeast.com/antarcticas-ice-sheet-is-melting-three-times-faster-than-we-thought

Extract: "Antarctica’s ice sheet is melting three times faster than previously forecasted, according to a report published Wednesday in the journal Nature by 80 scientists. The team said that the ice sheet is melting so fast that 219 billion tons of ice is pouring into the ocean annually—enough to raise sea levels by a half millimeter per year. Between 1992 and 1997, Antarctica was losing 49 billion times of ice per year; from 2012 to 2017, that number increased more than eightfold, according to the Ice Sheet Mass Balance Inter-comparison Exercise. At this rate of acceleration, scientists warn that oceans would rise faster than ever, which means a reduced amount of time for low-lying communities to prepare adequately. “We’re still talking about roughly a half a millimeter per year,” one scientist told The Washington Post. “That isn’t going to sound horribly unmanageable. But remember for the northern hemisphere, for North America, the fact that the location in West Antarctica is where the action is amplifies that rate of sea level rise by up to an about additional 25 percent in a city like Boston or New York.”"

[gerontocrat]

The NOAA recently produced its 2017 report and data on C02e for 2017.

The graph below is from their data. Note how the annual increase in other gases other than CO2 is really flat. I added the CH4 (methane) element to the graph.

The second image is the map of the monitoring stations that NOAA use

(https://www.esrl.noaa.gov/gmd/aggi/aggi.html)

Observations
The NOAA monitoring program provides high-precision measurements of the global abundance and distribution of long-lived greenhouse gases that are used to calculate changes in radiative climate forcing.

Air samples are collected through the NOAA/ESRL global air sampling network, including a cooperative program for the carbon gases which provides samples from ~80 global background air sites, including measurements at 5 degree latitude intervals from ship routes

The map shows that monitoring stations in the Arctic tundra are sparse or non-existent.

So - is NOAA underestimating emissions from melting permafrost on the tundra and the shallow seas of the Eastern Siberian Arctic Shelf?

[AbruptSLR]

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.

[AbruptSLR]

Warm Atlantic waters are increasingly invading the north Barents Sea, and rapidly transitioning it from an Arctic-type to an Atlantic-type of climate regime & this is occurring faster than consensus climate science models have projected:

Lind, et al. (2018), "Arctic warming hotspot in the northern Barents Sea linked to declining sea-ice import", Nature Climate Change; https://doi.org/10/s41558-018-0205-y

http://www.nature.com/articles/s41558-018-0205-y

Extract: "Thus, the northern Barents Sea may soon complete the transition from a cold and stratified Arctic to a warm and well-mixed Atlantic-dominated climate regime."

[jai mitchell]

https://t.co/1w3U1O2ivK

Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond

This paper uses new constraints on long-term impacts to the earth's system under much warmer paleoclimate regimes.  It indicates that current models used are vastly underestimating historic Arctic Amplification and that some land-ice feedbacks not included in the models due to their perceived timeline of impact should be included as these feedbacks are much more rapid than modeled. 

Using their model and adjusting for current conditions (reduced land ice as we are in an interglacial) they find that the ECS for 2XCO2 is closer to 7C than 3C.

The EECO simulations that include the effect of surface albedo (blue triangles) are closer to the palaeo reconstructions, but still underestimate the inferred EECO warming at high CO2

[jai mitchell]

"On the Contrary, our results suggest that, if anything, model shortcomings can be used to reject the least severe projections"

https://www.youtube.com/watch?v=mBP1kO1yrh4&t=2m34s

[AbruptSLR]

The CMIP5 model runs in AR5 do not account for the influence of ice sheets and only a few approximated the influence of ice shelves.  However, the reference research demonstrates that improved modeling of ice shelves using the models in CMIP5 that considered the approximate influence of ice shelves indicate dramatic increases of basal ice melting and particularly for the ice shelves in the Amundsen Sea area, see the attached images.  Thus, over-relying on AR5 projections is subjecting the world to higher climate change risks and policymakers currently acknowledge.

Kaitlin A. Naughten et al (2018), "Future Projections of Antarctic Ice Shelf Melting Based on CMIP5 Scenarios, Journal of Climate, https://doi.org/10.1175/JCLI-D-17-0854.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0854.1

Abstract: "Basal melting of Antarctic ice shelves is expected to increase during the twenty-first century as the ocean warms, which will have consequences for ice sheet stability and global sea level rise. Here we present future projections of Antarctic ice shelf melting using the Finite Element Sea Ice/Ice-Shelf Ocean Model (FESOM) forced with atmospheric output from models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). CMIP5 models are chosen based on their agreement with historical atmospheric reanalyses over the Southern Ocean; the best-performing models are ACCESS 1.0 and the CMIP5 multimodel mean. Their output is bias-corrected for the representative concentration pathway (RCP) 4.5 and 8.5 scenarios. During the twenty-first-century simulations, total ice shelf basal mass loss increases by between 41% and 129%. Every sector of Antarctica shows increased basal melting in every scenario, with the largest increases occurring in the Amundsen Sea. The main mechanism driving this melting is an increase in warm Circumpolar Deep Water on the Antarctic continental shelf. A reduction in wintertime sea ice formation simulated during the twenty-first century stratifies the water column, allowing a warm bottom layer to develop and intrude into ice shelf cavities. This effect may be overestimated in the Amundsen Sea because of a cold bias in the present-day simulation. Other consequences of weakened sea ice formation include freshening of High Salinity Shelf Water and warming of Antarctic Bottom Water. Furthermore, freshening around the Antarctic coast in our simulations causes the Antarctic Circumpolar Current to weaken and the Antarctic Coastal Current to strengthen."

See also, Title: "Future projections of Antarctic ice shelf melting"

https://www.skepticalscience.com/future-projections-antarctic-ice-shelf-melt.html

Extract: "Climate models don’t typically include ice sheets, or ice shelves, or icebergs. This is one reason why projections of sea level rise are so uncertain. But some standalone ocean models do include ice shelves. At least, they include the little pockets of ocean beneath the ice shelves – we call them ice shelf cavities – and can simulate the melting and refreezing that happens on the ice shelf base.

We took one of these ocean/ice-shelf models and forced it with the atmospheric output of regular climate models, which periodically make projections of climate change from now until the end of the century. We completed four different simulations, consisting of two different greenhouse gas emissions scenarios (“Representative Concentration Pathways” or RCPs) and two different choices of climate model (“ACCESS 1.0”, or “MMM” for the multi-model mean). Each simulation required 896 processors on the supercomputer in Canberra. By comparison, your laptop or desktop computer probably has about 4 processors. These are pretty sizable models!

In every simulation, and in every region of Antarctica, ice shelf melting increased over the 21st century. The total increase ranged from 41% to 129% depending on the scenario. The largest increases occurred in the Amundsen Sea region, marked with red circles in the maps below, which happens to be the region exhibiting the most severe melting in recent observations. In the most extreme scenario, ice shelf melting in this region nearly quadrupled.
So what processes were causing this melting? This is where the sea ice comes in. When sea ice forms, it spits out most of the salt from the seawater (brine rejection), leaving the remaining water saltier than before. Salty water is denser than fresh water, so it sinks. This drives a lot of vertical mixing, and the heat from warmer, deeper water is lost to the atmosphere. The ocean surrounding Antarctica is unusual in that the deep water is generally warmer than the surface water. We call this warm, deep water Circumpolar Deep Water, and it’s currently the biggest threat to the Antarctic Ice Sheet. (I say “warm” – it’s only about 1°C, so you wouldn’t want to go swimming in it, but it’s plenty warm enough to melt ice.)

In our simulations, warming winters caused a decrease in sea ice formation. So there was less brine rejection, causing fresher surface waters, causing less vertical mixing, and the warmth of Circumpolar Deep Water was no longer lost to the atmosphere. As a result, ocean temperatures near the bottom of the Amundsen Sea increased. This better-preserved Circumpolar Deep Water found its way into ice shelf cavities, causing large increases in melting.

Slices through the Amundsen Sea – you’re looking at the ocean sideways, like a slice of birthday cake, so you can see the vertical structure. Temperature is shown on the top row (blue is cold, red is warm); salinity is shown on the bottom row (blue is fresh, red is salty). Conditions at the beginning of the simulation are shown in the left 2 panels, and conditions at the end of the simulation are shown in the right 2 panels. At the beginning of the simulation, notice how the warm, salty Circumpolar Deep Water rises onto the continental shelf from the north (right side of each panel), but it gets cooler and fresher as it travels south (towards the left) due to vertical mixing. At the end of the simulation, the surface water has freshened and the vertical mixing has weakened, so the warmth of the Circumpolar Deep Water is preserved. Figure 8 of Naughten et al., 2018, © American Meteorological Society.

This link between weakened sea ice formation and increased ice shelf melting has troubling implications for sea level rise. Unfortunately, models like the one we used for this study can’t actually be used to simulate sea level rise, as they have to assume that ice shelf geometry stays constant. No matter how much ice shelf melting the model simulates, the ice shelves aren’t allowed to thin or collapse. Basically, this design assumes that any ocean-driven melting is exactly compensated by the flow of the upstream glacier such that ice shelf geometry remains constant.

Of course this is not a good assumption, because we’re observing ice shelves thinning all over the place, and a few have even collapsed. But removing this assumption would necessitate coupling with an ice sheet model, which presents major engineering challenges. We’re working on it – at least ten different research groups around the world – and over the next few years, fully coupled ice-sheet/ocean models should be ready to use for the most reliable sea level rise projections yet."

[jai mitchell]

https://newsroom.unsw.edu.au/news/science-tech/global-warming-may-be-twice-what-climate-models-predict

Global warming may be twice what climate models predict

A new study based on evidence from past warm periods suggests global warming may be double what is forecast.

The findings published last week in Nature Geoscience are based on observational evidence from three warm periods over the past 3.5 million years when the world was 0.5°C-2°C warmer than the pre-industrial temperatures of the 19th Century.

The research also revealed how large areas of the polar ice caps could collapse and significant changes to ecosystems could see the Sahara Desert become green and the edges of tropical forests turn into fire dominated savanna.

“Observations of past warming periods suggest that a number of amplifying mechanisms, which are poorly represented in climate models, increase long-term warming beyond climate model projections,” said lead author, Prof Hubertus Fischer of the University of Bern.

Paper here:  https://www.nature.com/articles/s41561-018-0146-0

Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond

Abstract: 

Over the past 3.5 million years, there have been several intervals when climate conditions were warmer than during the pre-industrial Holocene. Although past intervals of warming were forced differently than future anthropogenic change, such periods can provide insights into potential future climate impacts and ecosystem feedbacks, especially over centennial-to-millennial timescales that are often not covered by climate model simulations. Our observation-based synthesis of the understanding of past intervals with temperatures within the range of projected future warming suggests that there is a low risk of runaway greenhouse gas feedbacks for global warming of no more than 2 °C. However, substantial regional environmental impacts can occur. A global average warming of 1–2 °C with strong polar amplification has, in the past, been accompanied by significant shifts in climate zones and the spatial distribution of land and ocean ecosystems. Sustained warming at this level has also led to substantial reductions of the Greenland and Antarctic ice sheets, with sea-level increases of at least several metres on millennial timescales. Comparison of palaeo observations with climate model results suggests that, due to the lack of certain feedback processes, model-based climate projections may underestimate long-term warming in response to future radiative forcing by as much as a factor of two, and thus may also underestimate centennial-to-millennial-scale sea-level rise.

[Michael Hauber]

This thread started four years ago.  I recall lots of claims that new evidence implied a much greater climate sensitivity than the IPCC range.

Four years down the track, and the latest papers on climate sensitivity still seem to agree with IPCC.

First few from the google search that comment on possible values for climate sensitivity.
Emergent constraint on equilibrium climate sensitivity from global temperature variability  best estimate 2.8, likely range 2.2 to 3.4.  IPCC range is 1.5 to 4.5.
Global warming projections to 2100 using simple CO2 greenhouse gas modeling and comments on CO2 climate sensitivity factor Co2 sensitivity factor is 2.52, compared to IPCC 4.33.  Red flags on this paper include reference to Loehle and Scafetta, and statement of a value to 2 decimal places without a range.
Climate sensitivity estimates – sensitivity to radiative forcing time series and observational data Effective climate sensitivity is 1.9C, range 1.2 to 3.1.  Note effective not equilibrium.  Abstract claims consistency with IPCC and with models
Energy budget constraints on climate sensitivity in light of inconstant climate feedbacks  Equilibrium climate sensitivity 2.9.  Range 1.9-7.1

I note they are all largely observational based estimates.  I scan through to the second page to find something more model based.

The role of Hadley cell extent in determining the radiative effect of midlatitude clouds, and the resulting effects on CMIP5 models' climate sensitivity

No specific value for sensitivity in abstract, but they find that models with a realistic hadley cell expansion have a significantly lower climate sensitivity than models that over-estimate hadley cell expansion.  I haven't kept up with this thread for quite some time, did this paper get as much exposure on this thread as the papers finding higher climate sensitivity for models that have a more realistic representation of clouds?


Also since 2014, modern global temp trends (GISS, from 1975 as per Tamino breakpoint analysis) have increased from 1.66 C/century to 1.82 C/century.  This is still not as high as the highest temperature trend pre-pause at 1.88 C/century (1975 to mid 2017), or the CMIP5 trend of 2.25 C/century.

I also note that yet again the usual suspects have been convinced that this would be the year that Arctic ice would crash, and yet again the minimum looks like failing to seriously challenge 2012's record.  Assuming no amazing finish to the melt season this will be the equal longest period failing to set a new melt record in the ADS data set, equaling the previous record of 6 years between 1984 and 1990.

This thread started in 2014, and the period from 2014 is still kind of short to expect much change.  But serious projections of global warming started in the late 70s.  Today's estimates of climate sensitivity have not been significantly changed by the last 30-40 years of data.  Projections of temperature change have not changed substantially.  We have been close to, and maybe a little lower than these projections.

[jai mitchell]

Dessler &  Forster - 3.3K https://eartharxiv.org/4et67
Paynter et. al. - 3.3K and 4.8K  https://www.researchgate.net/profile/Levi_Silvers/publication/322776893_Equilibrium_Climate_Sensitivity_Obtained_from_Multi-Millennial_Runs_of_Two_GFDL_Climate_Models/links/5a7a0e1aa6fdccebdd81909d/Equilibrium-Climate-Sensitivity-Obtained-from-Multi-Millennial-Runs-of-Two-GFDL-Climate-Models.pdf
Caldwell et. al. - emerging constraints show higher sensitivities between 3.4 and 5.2K  https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-17-0631.1 (reported values inside paper)
Qu et. al.  (see fig 1.) climate constraints on CMIP5 models show models have significantly low bias and for all 4 constraints, the observational values indicate ECS >4.0K  https://www.researchgate.net/profile/Xin_Qu2/publication/320954837_On_the_Emergent_Constraints_of_Climate_Sensitivity/links/5a57e2cfaca2726376b70d9f/On-the-Emergent-Constraints-of-Climate-Sensitivity.pdf
Frey & Kay Adjustment of models to include observations on supercoold cloud shortwave feedbacks show ECS between 4.1K and 5.6K  https://link.springer.com/article/10.1007/s00382-017-3796-5

It should be noted, however that the majority of the discussion regarding the low-balling of ECS is explained to be a function of how ECS is defined, which short term feedbacks are included or excluded. 

For example,, none of the models include carbon cycle response feedbacks from melting permafrost which effectively reduces the amount of anthropogenic emissions of carbon to achieve 2XCO2 nor do they include land-based feedbacks that are already being observed to be in decline (sinks).

Finally, it should also be noted that the current body of climate models still being used today are still underepresenting both the rate of albedo shift in the Arctic and do not accurately model the albedo response even when sea ice is lost - as shown by observations from NASA of the Beaufort Sea.

So, to suggest that we must rely on continued statements regarding ECS without critically analyzing their sets of assumptions and shortcomings (since we are actually trying to get to the real world impacts of CO2 that are only loosely attached to ECS - as it is currently defined) is really not effective.  Not until they change the definition of ECS or come up with a new definition like ESS (short-term).

[AbruptSLR]

This is the type of trigger that could lead to a collapse of the WAIS this century:

Title: "Slowdown of Atlantic conveyor belt could trigger ‘two decades’ of rapid global warming"

https://www.carbonbrief.org/slowdown-atlantic-conveyor-belt-could-trigger-two-decades-rapid-global-warming

Extract: "A slowdown in the Atlantic Ocean current bringing warm water up to Europe from the tropics could trigger “a period of rapid global surface warming”, a new study suggests.

The research, published in Nature, says that a recent weakening of the “Atlantic Meridional Overturning Circulation” (AMOC) is coming to an end, but will stay at a “prolonged minimum” for the next two decades.

See also:

http://www.nature.com/articles/s41586-018-0320-y.epdf?referrer_access_token=S6k9dOfchK34XxUTYELy_NRgN0jAjWel9jnR3ZoTv0Ptia3hkCpjkCV6kA0JU4C3i_vb6r0jGDG0JbxpCb-xOuz_fX2804bSVcLl4-PbDwgpRiMAFIwyREht0zwX87zI4O0ghtB3QfbPIkbCoBItpmhArMOvC32jK9lfmgDcU83a1e9BJ61WjK74T3ZfR4FIGmY0tSanxYAtjZ2x8dqIkobQcZrSRrM0BjjZH5c7d9S7FQjH5sdOznmms9R9xwtCYex1MKyhX1iVS76qW1lA9966b6ueTqrgnbbxOWo3N88%3D&tracking_referrer=www.carbonbrief.org

[Michael Hauber]

Dessler & Forster.  Mode 2.9k, median 3.3k.  Quite consistent with IPCC.
Paynter et al.  3.3k and 4.8k are two individual models.  CMIP5 models range from 2 to 4.5, so pretty much in the range.  However both models are found to be one degree higher than the corresponding value quoted for that model by IPCC due to a different method of defining ECS.
Caldwell et al.  models which match clouds the best have a high sensitivity(in this case 3.4 to 5.2)
Qu et al - again models which match clouds the best have a high sensitivity.  Last sentence from abstract - 'any proposed ECS constraint should not be taken at face value since other factors influencing ECS besides shortwave cloud feedback could be systematically biased in the models.'
Frey & Kay - again improving the accuracy of cloud feedbacks results in a model with a higher sensitivity.

It should be noted, however that the majority of the discussion regarding the low-balling of ECS is explained to be a function of how ECS is defined, which short term feedbacks are included or excluded. 

For example,, none of the models include carbon cycle response feedbacks from melting permafrost which effectively reduces the amount of anthropogenic emissions of carbon to achieve 2XCO2 nor do they include land-based feedbacks that are already being observed to be in decline (sinks).

Seems to me from what you posted, from what was discussed back near the start of this thread, and from quickly skimming the last two pages,  that the one piece of significant evidence for a higher sensitivity is the possibility of a much higher cloud feedback.  This is not a slow feedback or a carbon cycle issue.  Currently the modeled warming rate since 1975 is 2.2C per century, and observed 1.9C.  If a higher cloud feedback is included then surely the modelled rate from 1975 to now would go up to be even further above the observed rate.

Finally, it should also be noted that the current body of climate models still being used today are still underepresenting both the rate of albedo shift in the Arctic and do not accurately model the albedo response even when sea ice is lost - as shown by observations from NASA of the Beaufort Sea.

By how much?  And again if a stronger Arctic ice feedback is put into the models then the models would presumably further overestimate the currently observed warming. 

Best image on Arctic Sea ice decline I can find is



Big gap between obs and model in 2012, but we are in 2018, and looks like we should be somewhere 4.5 to 5m.  Last year was 4.47m by ADS, 16 and 17 closer to 4m, and to date we are 500k more ice than last year.  so I'd say that the slowdown since 2012 we are still a little less than model but the gap is getting quite narrow - about the same size as the gap between observations and modelling for global temps.

[jai mitchell]

Logically ASI loss changes in albedo may be insignificant on a global basis, due to quite a small area involved plus being the pole the relative insolation (sun intensity overall) is quite small versus the rest of the planet. And for example this year's summer period and others have shown increased cloud clover haven't they?

while the overall area is small and the time of intense sunlight in the arctic is short, NASA has already documented a 50 W/meter-squared increase in absorbed solar energy over the beaufort sea. 

On an annual basis, since the intensity of sunlight in the Arctic on summer solstice over a 24 hour period is actually more than that of the equator (by about 15%), the annual average increase due to a June 21 ice free arctic is about 0.3 W/meter-squared (globally averaged)  however, it is not going to be globally averaged but rather focused intensely on the Arctic.  Modeled studies I have seen show a +8C regional warming over the Arctic when this happens.  Note that this is no currently being evidence (much) in terms of Arctic Amplification which has been largely forced by increased water vapor, meridional flows and shifts in the Polar Vortex during the Winter Months.

With regard to michael's comment, the cloud forcing that is now being defined (which we have already shown in this thread through multiple lines of evidence to be understated by the climate models) and it shows what we have already suspected, with an upper bound from this impact only of ~3.7C ECS.  However, our projections are not based on historical observational constraints but rather the impacts under future warming conditions, especially under the regime of much lower tropical SO2 atmospheric loading, leading to even fewer cloud regimes and greater expansion of the Hadley Cell.

The short term feedbacks that I would include in the discussion of  ECS are glacier and sea ice feedbacks and near-term carbon cycle feedbacks, which would shift the term "ECS" to "ECScc" which would deduct the CO2e value of net positive carbon cycle emissions through 2100 from the total weight of CO2 needed to achieve 2XCO2 and scale it accordingly to temperature response.

Since this is how ECS is being used in common parlance (i.e. the media)  in terms of total warming potential.  This would shift the terms of the conversation to include those responses and earth system dynamics that are currently being left out of the assessment. 

[Michael Hauber]

With regard to michael's comment, the cloud forcing that is now being defined (which we have already shown in this thread through multiple lines of evidence to be understated by the climate models) and it shows what we have already suspected, with an upper bound from this impact only of ~3.7C ECS.  However, our projections are not based on historical observational constraints but rather the impacts under future warming conditions, especially under the regime of much lower tropical SO2 atmospheric loading, leading to even fewer cloud regimes and greater expansion of the Hadley Cell.

Yes the models that model clouds better have a higher ECS.  I already acknowledged that.  But what about the fact that the models are already over predicting the warming rate, and increasing cloud feedbacks would presumably make that worse?  Do you have a response to that issue?  Or is your response that 'projections are not based on observational constraints'.  Is this a fancy way of saying 'We are ignoring reality'?

[jai mitchell]

With regard to michael's comment, the cloud forcing that is now being defined (which we have already shown in this thread through multiple lines of evidence to be understated by the climate models) and it shows what we have already suspected, with an upper bound from this impact only of ~3.7C ECS.  However, our projections are not based on historical observational constraints but rather the impacts under future warming conditions, especially under the regime of much lower tropical SO2 atmospheric loading, leading to even fewer cloud regimes and greater expansion of the Hadley Cell.

Yes the models that model clouds better have a higher ECS.  I already acknowledged that.  But what about the fact that the models are already over predicting the warming rate, and increasing cloud feedbacks would presumably make that worse?  Do you have a response to that issue?  Or is your response that 'projections are not based on observational constraints'.  Is this a fancy way of saying 'We are ignoring reality'?

As I have stated and shown along multiple lines of evidence, the impacts of Aerosols on global circulation patterns, especially in regard to cloud effects and PDO/AMO are NOT represented in the models.  This is why we had a 'pause' and why we are starting to see the rapid increase in warming and shift to (probably) another El Nino this year.

If I am correct, the SO2 impact of the models is understating their cooling impact by much more than the 0.7C (median estimate) from this recent study (but still much more than the CMIP5 model mean):  https://nationalpost.com/news/world/scrubbing-aerosol-particles-from-the-atmosphere-a-faustian-bargain-study-finds

[S.Pansa]

But what about the fact that the models are already over predicting the warming rate ...

Are they?
Going by the updated IPCC graph (Figure 11.25a) taken from this article on climate-lab-book, models and actual mean temperatures match quite well (see first pic below).

If you further take into account that:
1) CIMP5 forcings from 2005 onwords do differ from those in real life [see second pic from this real climate article]

2) and the fact that the comparisons above do not compare apples with apples (see for that this article from Kevin Cowton & pic 3)

I wouldn't be so sure that the "fact that the models are already over predicting the warming rate" is really a fact anymore.

Edit: Sorry just realised that the graph taken from the Real Climate article does already account for the use of SST instead of SAT. From the caption:

Forcing adjustment is updated from Schmidt et al. (2014). Observations are the standard quasi-global estimates of anomalies with no adjustment for spatial coverage or the use of SST instead of SAT over the open ocean. Last updated 20 Jan 2018.

Nonetheless: it shows the models beeing bang on the money.

[Michael Hauber]

But what about the fact that the models are already over predicting the warming rate ...

Are they?

Yes, but only by a quite small amount, which shows up quite well in your last graph.  The argument here is not that the models are overpredicting observed warming by a significant amount so as to throw doubt on model performance.  The argument is that as the models are overpredicting observed warming, then claiming that they are overly conservative is an extraordinary claim requiring extraordinary evidence.

Nonetheless: it shows the models beeing bang on the money.

Agree, and i think claims they are overly conservative and need to be revised upwards are silly.

[jai mitchell]

Agree, and i think claims they are overly conservative and need to be revised upwards are silly.

So do you have an argument why my statement is incorrect?

If I am correct, the SO2 impact of the models is understating their cooling impact by much more than the 0.7C (median estimate) from this recent study (but still much more than the CMIP5 model mean):  https://nationalpost.com/news/world/scrubbing-aerosol-particles-from-the-atmosphere-a-faustian-bargain-study-finds

and, of course, you posit that historic performance of models indicates that their projections of future warming are not understating the likely reality even though we already know that they do not include permafrost emissions, severely understate the non-permafrost land-based carbon cycle feedbacks, understate cloud regime changes, do not include ocean aerosol reductions under future ocean acidification and understate both the speed and impact of Arctic Sea ice loss (especially under a rapid SO2 emissions reduction projection).

I think that you are being silly.

[Michael Hauber]

If I am correct, the SO2 impact of the models is understating their cooling impact by much more than the 0.7C (median estimate) from this recent study (but still much more than the CMIP5 model mean):  https://nationalpost.com/news/world/scrubbing-aerosol-particles-from-the-atmosphere-a-faustian-bargain-study-finds

Thats not a study but a news article.  The first link finds a study that runs some climate models and finds that removing aerosols accounts for 0.5 to 1 degree of warming.  It presents zero evidence that the models are understating the amount of cooling due to aerosols.

and, of course, you posit that historic performance of models indicates that their projections of future warming are not understating the likely reality even though we already know that they do not include permafrost emissions, severely understate the non-permafrost land-based carbon cycle feedbacks, understate cloud regime changes, do not include ocean aerosol reductions under future ocean acidification and understate both the speed and impact of Arctic Sea ice loss (especially under a rapid SO2 emissions reduction projection).

I think that you are being silly.

Permafrost has been melting for the last 40 years.  Land-based carbon cycle feedbacks have been occuring for the last 40 years.  Cloud regimes have been changing for the last 40 years.  Aerosols have been changing due to ocean acidification for 40 years.  The Arctic ice has been melting for 40 years.

If these factors are going to cause the temperature to warm faster than the models, then why have they not done so for the last 40 years?

[Michael Hauber]

Because all the models are wrong - they are useful not perfection. Close enough is often good enough.

Yes so we could certainly end up with more warming in the future than forecast.  Or we could end up with less warming than predicted. 

PS When will the 0.5C supposedly already built into the climate system but not yet showing up as observed surface / ocean Temperature anomalies going to appear and how fast will it appear? Is this already detailed in past and future modelling efforts?

How else could we possibly measure the warming built into the climate system but with models?

[Bruce Steele]

Jai mentioned acidification and future reductions in DMS ( Dimethyl sulfide ) as a potential positive feedback not included in forecasts. We are headed into a world with much larger areas of ocean surfaces that will be exposed to aragonite undersaturation in polar oceans and eastern  boundary current upwelling areas. Undersaturation results in a change in phytoplankton communities . Those community phytoplankton changes result in a decrease of DMS production, less clouds and increased insolation. Currently modeled as a weak positive feedback.
 https://link.springer.com/article/10.1007/s10533-018-0430-5

" Comparisons between parallel simulations with and without DMS fluxes into the atmosphere show significant differences in marine ecosystems and physical fields. Without DMS, the missing subsequent aerosol indirect effects on clouds and radiative forcing lead to fewer clouds, more solar radiation, and a much warmer climate."

This is an example of a chemical threshold , undersaturation, that results in biological responses only once that threshold is crossed. It is coming but we can't look at past trends to see the signal . I would agree with Jai that there are  positive feedbacks not incorporated into current models. There are also some negative feedbacks not incorporated . If however the Arctic Summer's cloudiness is reduced in the future as ocean acidification advances then potentially the positive feedbacks of less DMS production will counteract some of the negative feedbacks that Arctic  summer cloudiness currently produces.

[jai mitchell]

WRT Millar et. al. and other carbon budgets  https://twitter.com/BrigitteKnopf/status/1020916210622484480

The 'rebasing' of warming periods extracts the warming that is anthropogenic from that which has been deemed 'natural variability'  This then adds to the carbon budget by reducing the amount of warming that has been observed that is anthropogenic (from what we are actually experiencing). 

My confidence in our ability to identify and extract the natural variability component is nil.

It has already been shown that the differences in aerosol emissions loading and distribution over the last 2 decades has significantly impacted the PDO/AMO/AMOC and AO.  These are not natural variations.

[jai mitchell]

Permafrost has been melting for the last 40 years.  Land-based carbon cycle feedbacks have been occuring for the last 40 years.  Cloud regimes have been changing for the last 40 years.  Aerosols have been changing due to ocean acidification for 40 years.  The Arctic ice has been melting for 40 years.

Not so much

The reason the 0.5C to 1.0C of cooling by current aerosols is more than the CMIP5 model mean used in the IPCC AR5 is because it is. 

and https://www.nature.com/articles/nature03671

[Michael Hauber]

That paper provides no evidence of a higher aerosol forcing.  It only looks at what the implications of a higher aerosol forcing for climate sensitivity.  To quote from the paper

The range of aerosol forcings predicted by ‘forward’ models, using our best knowledge on the atmospheric aerosol burden and its climate effects, is vast, from 0 to 4.4 Wm2

IPCC 5 aerosol forcing is stated as -1.9 to  0.1 w/m2.  Total anthropogenic net forcing is stated as 1.1 to 3.3 2/m2.  A net forcing of 1.1, and net aerosol forcing of -1.9, a current warming of 1C would imply that aerosols are currently causing about 2C of cooling.  Probably also corresponds to a climate sensitivity at the upper end, but half that if climate sensitivity is moderate.  Therefore a range of 0.5 to 1C for aerosol cooling is not at all inconsistent with the IPCC range.

[jai mitchell]

That paper provides no evidence of a higher aerosol forcing.  It only looks at what the implications of a higher aerosol forcing for climate sensitivity.  To quote from the paper

The range of aerosol forcings predicted by ‘forward’ models, using our best knowledge on the atmospheric aerosol burden and its climate effects, is vast, from 0 to 4.4 Wm2

IPCC 5 aerosol forcing is stated as -1.9 to  0.1 w/m2.  Total anthropogenic net forcing is stated as 1.1 to 3.3 2/m2.  A net forcing of 1.1, and net aerosol forcing of -1.9, a current warming of 1C would imply that aerosols are currently causing about 2C of cooling.  Probably also corresponds to a climate sensitivity at the upper end, but half that if climate sensitivity is moderate.  Therefore a range of 0.5 to 1C for aerosol cooling is not at all inconsistent with the IPCC range.

This is an interesting way to go about things.  Did you consider that we are no where near equilibrium, that we have experienced about 1.2C of total warming already with a current Earth System Energy Imbalance EEI (AKA TOA) of 0.9 W/m^2?

So you are basically saying then that we are at equilibrium warming, that we experience that equilibrium warming of 0. W/m^2 of total net forcing (1.1 - 0.9 W/m^2) and that this total net forcing produced a warming of 1.2C?

I think it is pretty obvious that your entire methodology is flawed, considerably.

[Michael Hauber]

To guestimate some figures, at equilibrium net anthropogenic climate forcing might be 4.5, temperature change 3, total aerosol forcing -1.  In that case aerosol cooling would work out at -0.75. 

Your argument fails to notice the difference between top of atmosphere radiation imbalance and net forcing.  This difference is change in long wave radiation in response to change in temperature.

[jai mitchell]

To guestimate some figures, at equilibrium net anthropogenic climate forcing might be 4.5, temperature change 3, total aerosol forcing -1.  In that case aerosol cooling would work out at -0.75. 

Your argument fails to notice the difference between top of atmosphere radiation imbalance and net forcing.  This difference is change in long wave radiation in response to change in temperature.

Temperature at equilibrium is the equilibrium temp at current forcing.  Forcing doesn't change in this analysis (though it will change from albedo and increased carbon cycle emissions)  In this analysis the TOA radiative imbalance is the current remainder of forcing that needs to reach zero before surface temperatures achieve equilibrium, (regardless of the initial forcing).

[AbruptSLR]

Strong evidence of mankind's fingerprints on climate:

Benjamin D. Santer et al.  (20 Jul 2018), "Human influence on the seasonal cycle of tropospheric temperature", Science , Vol. 361, Issue 6399, eaas8806, DOI: 10.1126/science.aas8806

http://science.sciencemag.org/content/361/6399/eaas8806

Structured Abstract

INTRODUCTION
Fingerprint studies use pattern information to separate human and natural influences on climate. Most fingerprint research relies on patterns of climate change that are averaged over years or decades. Few studies probe shorter time scales. We consider here whether human influences are identifiable in the changing seasonal cycle. We focus on Earth’s troposphere, which extends from the surface to roughly 16 km at the tropics and 13 km at the poles. Our interest is in TAC, the geographical pattern of the amplitude of the annual cycle of tropospheric temperature. Information on how TAC has changed over time is available from satellite retrievals and from large multimodel ensembles of simulations.

RATIONALE
At least three lines of evidence suggest that human activities have affected the seasonal cycle. First, there are seasonal signals in certain human-caused external forcings, such as stratospheric ozone depletion and particulate pollution. Second, there is seasonality in some of the climate feedbacks triggered by external forcings. Third, there are widespread signals of seasonal changes in the distributions and abundances of plant and animal species. These biological signals are in part mediated by seasonal climate changes arising from global warming. All three lines of evidence provide scientific justification for performing fingerprint studies with the seasonal cycle.

RESULTS
The simulated response of the seasonal cycle to historical changes in human and natural factors has prominent mid-latitude increases in the amplitude of TAC. These features arise from larger mid-latitude warming in the summer hemisphere, which appears to be partly attributable to continental drying. Because of land-ocean differences in heat capacity and hemispheric asymmetry in land fraction, mid-latitude increases in TAC are greater in the Northern Hemisphere than in the Southern Hemisphere. Qualitatively similar large-scale patterns of annual cycle change occur in satellite tropospheric temperature data.

We applied a standard fingerprint method to determine (i) whether the pattern similarity between the model “human influence” fingerprint and satellite temperature data increases with time, and (ii) whether such an increase is significant relative to random changes in similarity between the fingerprint and patterns of natural internal variability. This method yields signal-to-noise (S/N) ratios as a function of increasing satellite record length. Fingerprint detection occurs when S/N exceeds and remains above the 1% significance threshold.

We find that the model fingerprint of externally forced seasonal cycle changes is identifiable with high statistical confidence in five out of six satellite temperature datasets. In these five datasets, S/N ratios for the 38-year satellite record vary from 2.7 to 5.8. Our positive fingerprint detection results are unaffected by the removal of all global mean information and by the exclusion of sea ice regions. On time scales for which meaningful tests are possible (one to two decades), there is no evidence that S/N ratios are spuriously inflated by a systematic model underestimate of the amplitude of observed tropospheric temperature variability.

CONCLUSION
Our results suggest that attribution studies with the seasonal cycle of tropospheric temperature provide powerful and novel evidence for a statistically significant human effect on Earth’s climate. We hope that this finding will stimulate more detailed exploration of the seasonal signals caused by anthropogenic forcing.

[AbruptSLR]

Seawater percolation into below sea level layers of the firn in Antarctic ice shelves is not a good thing, and is more widespread than previously assumed:

Cook, S., Galton-Fenzi, B. K., Ligtenberg, S. R. M., and Coleman, R.: Brief Communication: Widespread potential for seawater infiltration on Antarctic ice shelves, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-146, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-146/

Abstract. Antarctica's future contribution to sea level change depends on the fate of its fringing ice shelves. One variable which may affect the rates of iceberg calving from ice shelves is the presence of liquid water, including the percolation of seawater into permeable firn layers. Here, we present evidence that most ice shelves around Antarctica have regions where permeable firn exists below sea level. The findings indicate that seawater infiltration onto ice shelves may be much more widespread in Antarctica than previously recognised. Our results present the most likely locations for seawater infiltration to occur, and may be used as an indicator of where future radar studies might be focussed.

[AbruptSLR]

Further to my Reply #2299, the linked reference indicates that consensus climate models need to improve their representation of the stratosphere-troposphere coupling in order to better project coming extreme weather events, including those in Siberia:

Pengfei Zhang et al. (25 Jul 2018), "A stratospheric pathway linking a colder Siberia to Barents-Kara Sea sea ice loss", Science Advances, Vol. 4, no. 7, eaat6025, DOI: 10.1126/sciadv.aat6025

http://advances.sciencemag.org/content/4/7/eaat6025

Abstract: "Previous studies have extensively investigated the impact of Arctic sea ice anomalies on the midlatitude circulation and associated surface climate in winter. However, there is an ongoing scientific debate regarding whether and how sea ice retreat results in the observed cold anomaly over the adjacent continents. We present a robust “cold Siberia” pattern in the winter following sea ice loss over the Barents-Kara seas in late autumn in an advanced atmospheric general circulation model, with a well-resolved stratosphere. Additional targeted experiments reveal that the stratospheric response to sea ice forcing is crucial in the development of cold conditions over Siberia, indicating the dominant role of the stratospheric pathway compared with the direct response within the troposphere. In particular, the downward influence of the stratospheric circulation anomaly significantly intensifies the ridge near the Ural Mountains and the trough over East Asia. The persistently intensified ridge and trough favor more frequent cold air outbreaks and colder winters over Siberia. This finding has important implications for improving seasonal climate prediction of midlatitude cold events. The results also suggest that the model performance in representing the stratosphere-troposphere coupling could be an important source of the discrepancy between recent studies."

See also:
Cartier, K. M. S. (2018), Why are Siberian temperatures plummeting while the Arctic warms?, Eos, 99, https://doi.org/10.1029/2018EO103403. Published on 26 July 2018.

https://eos.org/articles/why-are-siberian-temperatures-plummeting-while-the-arctic-warms?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz072718

Extract: "The team is currently exploring whether the stratosphere plays a similar role in linking regional sea ice loss to extreme weather events in the northern reaches of North America."

[AbruptSLR]

The linked reference estimates that the 1.5C carbon budget should be reduced by about five years from previous consensus estimates.  Just imagine how big this feedback will be after we exceed 2C.

Edward Comyn-Platt  et al. (2018), "Carbon budgets for 1.5 and 2 °C targets lowered by natural wetland and permafrost feedbacks", Nature Geoscience, volume 11, pages568–573, https://doi.org/10.1038/s41561-018-0174-9

https://www.nature.com/articles/s41561-018-0174-9

Extract: "Global methane emissions from natural wetlands and carbon release from permafrost thaw have a positive feedback on climate, yet are not represented in most state-of-the-art climate models. Furthermore, a fraction of the thawed permafrost carbon is released as methane, enhancing the combined feedback strength."

See also:
https://www.skepticalscience.com/permafrost-wetland-emissions-cut-budget-5-years.html

[AbruptSLR]

Newly identified evidence indicates that the Southern Ocean will likely stop absorbing as much CO₂ as it recently has been doing, with continuing anthropogenic radiative forcing:

Title: "How much longer will Southern Ocean slow climate change?"

http://www.newstalkzb.co.nz/news/national/how-much-longer-will-southern-ocean-slow-climate-change/

Extract: "The vast and wild ocean current sucks up more than 40 per cent of the carbon dioxide we produce, acting as a temporary climate-change buffer by slowing down the accumulation of greenhouse gases in our atmosphere.

Yet the same westerly winds that play a critical role in regulating its storing capacity are now threatening its future as a CO2 bank, by bringing deep carbon-rich waters up to the surface.
Many climate models predict that the westerly winds overlying the ocean would get stronger if atmospheric greenhouse gas concentrations continued to risk.

A new international study suggests that in the past, strong westerlies have been linked to higher levels of atmospheric CO2 due to their impact on the Southern Ocean carbon balance.

That meant stronger westerlies could actually speed up climate change if mankind continued to emit as much CO2 as it does today.
…
"Our new records of the Southern Hemisphere westerly winds suggest there have been large changes in wind intensity over the past 12,000 years.

"This is in marked contrast to climate model simulations that predict only relatively small wind speed changes over the same period."
…
Yet, Mikaloff-Fletcher added, sea surface carbon data suggested that there was a reversal of this trend in the early 2000s, when the Southern Ocean began taking up carbon much more quickly, even though the westerlies didn't slow.

"The mechanisms behind this change still aren't fully explained, which makes it hard to predict whether this is a short-term effect or a long-term one," she said.

"The Macquarie study suggests that the sudden increase in Southern Ocean carbon uptake may not persist on longer timescales.""