Conservative Scientists & its Consequences

[AbruptSLR]

With even NOAA saying that we are pretty much at 500ppm on a CO2e basis, there should be much more discussion about the Miocene. The Pliocene is already in the rear-view mirror on a CO2e basis.

One problem with the Miocene analogy is that the Isthmus of Panama had not closed yet, so there may still be lessons to learn from the Pliocene.  In this regards, the linked reference indicates that the mid-Pliocene is frequently considered as a rough analogue to climate change this century.  The reported finding come from Pliocene Model Intercomparison Project (PlioMIP), which tends to err on the side of least drama.  Nevertheless, these finding indicate a marked expansion of the Hadley circulation (HC); which typically is an indicator of relatively strong associated positive climate feedback mechanism.

Shawn Corvec and Christopher G. Fletcher (2017), "Changes to the tropical circulation in the mid-Pliocene and their implications for future climate", Clim. Past, 13, 135–147, doi:10.5194/cp-13-135-2017

https://www.clim-past.net/13/135/2017/cp-13-135-2017.pdf

Abstract: "The two components of the tropical overturning circulation, the meridional Hadley circulation (HC) and the zonal Walker circulation (WC), are key to the re-distribution of moisture, heat and mass in the atmosphere. The mid- Pliocene Warm Period (mPWP; ~3.3–3 Ma) is considered a very rough analogue of near-term future climate change, yet changes to the tropical overturning circulations in the mPWP are poorly understood. Here, climate model simulations from the Pliocene Model Intercomparison Project (PlioMIP) are analyzed to show that the tropical overturning circulations in the mPWP were weaker than preindustrial circulations, just as they are projected to be in future climate change. The weakening HC response is consistent with future projections, and its strength is strongly related to the meridional gradient of sea surface warming between the tropical and subtropical oceans. The weakening of the WC is less robust in PlioMIP than in future projections, largely due to inter-model variations in simulated warming of the tropical Indian Ocean (TIO). When the TIO warms faster (slower) than the tropical mean, local upper tropospheric divergence increases (decreases) and the WC weakens less (more). These results provide strong evidence that changes to the tropical overturning circulation in the mPWP and future climate are primarily controlled by zonal (WC) and meridional (HC) gradients in tropical–subtropical sea surface temperatures."
 

[AbruptSLR]

CMIP5 models underestimate the emissions of geologic CH₄ produced over millions of years and stored in reservoirs beneath terrestrial permafrost, with continued warming:

Katrin Kohnert, Andrei Serafimovich, Stefan Metzger, Jörg Hartmann, Torsten Sachs. Strong geologic methane emissions from discontinuous terrestrial permafrost in the Mackenzie Delta, Canada. Scientific Reports, 2017; 7 (1) DOI: 10.1038/s41598-017-05783-2

http://www.nature.com/articles/s41598-017-05783-2

Abstract: "Arctic permafrost caps vast amounts of old, geologic methane (CH4) in subsurface reservoirs. Thawing permafrost opens pathways for this CH4 to migrate to the surface. However, the occurrence of geologic emissions and their contribution to the CH4 budget in addition to recent, biogenic CH4 is uncertain. Here we present a high-resolution (100 m × 100 m) regional (10,000 km²) CH4 flux map of the Mackenzie Delta, Canada, based on airborne CH4 flux data from July 2012 and 2013. We identify strong, likely geologic emissions solely where the permafrost is discontinuous. These peaks are 13 times larger than typical biogenic emissions. Whereas microbial CH4 production largely depends on recent air and soil temperature, geologic CH4 was produced over millions of years and can be released year-round provided open pathways exist. Therefore, even though they only occur on about 1% of the area, geologic hotspots contribute 17% to the annual CH4 emission estimate of our study area. We suggest that this share may increase if ongoing permafrost thaw opens new pathways. We conclude that, due to permafrost thaw, hydrocarbon-rich areas, prevalent in the Arctic, may see increased emission of geologic CH4 in the future, in addition to enhanced microbial CH4 production."

See also the associate article entitled: "Thawing permafrost releases old greenhouse gas"

https://www.sciencedaily.com/releases/2017/07/170719084810.htm

Extract: "The thawing permafrost soils in the Arctic regions might contribute to the greenhouse effect in two respects: on the one hand rising temperatures lead to higher microbial methane production close to the surface. On the other hand thawing subsurface opens increasingly pathways for old, geologic methane.
…
The conclusion of the authors: The warming climate triggers not only the natural production of biogenic methane, it can also lead to stronger emissions of fossil gas. This contributes significantly to the permafrost-carbon-climate feedback. Kohnert: "Therefore permafrost areas vulnerable to thawing warrant much more attention.""

[AbruptSLR]

The linked article investigates the role of vegetation masking under RCP 8.5 on the boreal forest region of northern Eurasia and finds a factor of 1.5 increase in spring surface air temperature (SAT) above that considered by prior research like CMIP5.  This is a key factor indicating that Arctic Amplification (& ECS) will likely be higher than projected in AR5:

Manabu Abe et. al. (19 August 2017), "Vegetation masking effect on future warming and snow albedo feedback in a boreal forest region of northern Eurasia according to MIROC-ESM", Journal of Geophysical Research Atmospheres, DOI: 10.1002/2017JD026957 

http://onlinelibrary.wiley.com/doi/10.1002/2017JD026957/abstract?utm_content=bufferfa31f&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "The earth system model, MIROC-ESM, in which the leaf area index (LAI) is calculated interactively with an ecological land model, simulated future changes in the snow water equivalent under the scenario of global warming. Using MIROC-ESM, the effects of the snow albedo feedback (SAF) in a boreal forest region of northern Eurasia were examined under the possible climate future scenario RCP8.5. The simulated surface air temperature (SAT) in spring greatly increases across Siberia and the boreal forest region, whereas the snow cover decreases remarkably only in western Eurasia. The large increase in SAT across Siberia is attributed to strong SAF, which is caused by both the reduced snow-covered fraction and the reduced surface albedo of the snow-covered portion due to the vegetation masking effect in those grid cells. A comparison of the future changes with and without interactive LAI changes shows that, in Siberia, the vegetation masking effect increases the spring SAF by about two or three times and enhances the spring warming by approximately 1.5 times. This implies that increases in vegetation biomass in the future are a potential contributing factor to warming trends and that further research on the vegetation masking effect is needed for reliable future projection."

[AbruptSLR]

Figure 5 of the reference on findings of the CloudSat & CALIPSO within the A-Train, shows a dramatic increase (more positive) in observed net cloud feedback as compared to prior assumptions.  This of course means that ECS is higher than previously assumed.

Graeme Stephens et. al. (2017), "CloudSat and CALIPSO within the A-Train: Ten years of actively observing the Earth system", BAMS, https://doi.org/10.1175/BAMS-D-16-0324.1

http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-16-0324.1?utm_content=bufferebbb9&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer
or
http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-16-0324.1

Abstract: "The more than 10 years of observations jointly collected by CloudSat and CALIPSO satellites has resulted in new ways of looking at aerosol, clouds, and precipitation and new discoveries about processes that connect them.

One of the most successful demonstrations of an integrated approach to observe Earth from multiple perspectives is the A-Train satellite constellation (e.g. Stephens et al., 2002). The science enabled by this constellation flourished with the introduction of the two active sensors carried by the NASA CloudSat and the NASA/CNES Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellites that were launched together on April 28th, 2006. These two missions have provided a 10-year demonstration of coordinated formation flying that made it possible to develop integrated products and that offered new insights on key atmospheric processes. The progress achieved over this decade of observations, summarized in this paper, clearly demonstrate the fundamental importance of the vertical structure of clouds and aerosol for understanding the influences of the larger scale atmospheric circulation on aerosol, the hydrological cycle, the cloud-scale physics and on the formation of the major storm systems of Earth. The research also underscored inherent ambiguities in radiance data in describing cloud properties and how these active systems have greatly enhanced passive observation. It is now clear that monitoring the vertical structure of clouds and aerosol is essential and a climate data record is now being constructed. These pioneering efforts are to be continued with EarthCARE mission planned for launch in 2019."

Caption: "Figure 5 Upper three panels are from Hartmann et al (1992) who estimate the contribution to the cloud radiative effects (CRE) of five classes of clouds as defined according to the ISCCP radiance classification (upper left). The bottom panels are the equivalent analysis but with classification determined by the radar-lidar data of CloudSat and CALIPSO where true cloud heights establish the types and cloud thickness (x axis) are from water and ice path information which is proportional to cloud optical depth. The differences in CRE between this latter analysis and that of Hartmann et al underscores the effects of misclassification of clouds on the interpretation of their radiative effects. Ci=cirrus, D.C.=Deep Convection, M.L.=multi-layer, AS=Altostratus, AC-Alto-cumulus, NS=Nimbostratus, St=stratus, SC=stratocumulus and Cu=cumulus."

[AbruptSLR]

The linked reference indicates that AR5 meaningfully underestimates future global warming from land use and land cover change (LULCC):

Natalie M Mahowald, Daniel Ward, Scott Doney, Peter Hess and James T Randerson (2017), "Are the impacts of land use on warming underestimated in climate policy?", Environmental Research Letters, https://doi.org/10.1088/1748-9326/aa836d

http://iopscience.iop.org/article/10.1088/1748-9326/aa836d
&
http://iopscience.iop.org/article/10.1088/1748-9326/aa836d/pdf

Abstract: "While carbon dioxide emissions from energy use must be the primary target of climate change mitigation efforts, land use and land cover change (LULCC) also represent an important source of climate forcing. In this study we compute time series of global surface temperature change separately for LULCC and non-LULCC sources (primarily fossil fuel burning), and show that because of the extra warming associated with the co-emission of methane and nitrous oxide with LULCC carbon dioxide emissions, and a co-emission of cooling aerosols with non-LULCC emissions of carbon dioxide, the linear relationship between cumulative carbon dioxide emissions and temperature has a two-fold higher slope for LULCC than for non-LULCC activities. Moreover, projections used in the Intergovernmental Panel on Climate Change (IPCC) for the rate of tropical land conversion in the future are relatively low compared to contemporary observations, suggesting that the future projections of land conversion used in the IPCC may underestimate potential impacts of LULCC. By including a "business as usual" future LULCC scenario for tropical deforestation, we find that even if all non-LULCC emissions are switched off in 2015, it is likely that 1.5°C of warming relative to the preindustrial era will occur by 2100. Thus, policies to reduce LULCC emissions must remain a high priority if we are to achieve the low to medium temperature change targets proposed as a part of the Paris Agreement. Future studies using integrated assessment models and other climate simulations should include more realistic deforestation rates and the integration of policy that would reduce LULCC emissions."

Extract: "Here we show that the slope of the cumulative carbon dioxide emissions and
temperature relationship is twice as high for LULCC than for non-LULCC processes
(Figure 2). This implies that carbon dioxide emissions from LULCC is associated
with twice the impact on climate as carbon dioxide emissions from non-LULCC
processes, at least until 2100."

[AbruptSLR]

The linked RealClimate article discusses the findings of Armour (2017) and Proistosescu & Huybers (2017), that compare CMIP5 findings of ECS vs 'instantaneous' climate sensitivity (ICS) based on observations (see previous posts).  However, I would like to note that since CMIP5 findings were published, numerous references have found that CMIP5 apparently errs on the side of least drama w.r.t. such areas (off the top of my head) as: Paleodata, Model Boundary Conditions/Parameters, Cloud feedback, Aerosol Forcings and Feedbacks, Permafrost Degradation, Methane Hydrates, Ice-Climate Feedback, Tropical Land Degradation & Changes in Land Albedo; Climate Attractors (ENSO, etc), Oceanic CO₂ Venting, Degradation of Oceanic CO₂ Sinks, Degradation of Land CO₂ Sinks, Arctic Amplification and Antarctic Amplification.  Therefore, we should not feel too comfortable that Armour (2017) and Proistosescu & Huybers (2017) represent the final increase in estimated ECS values.

Title: "Sensible Questions on Climate Sensitivity"

http://www.realclimate.org/index.php/archives/2017/08/sensible-questions-on-climate-sensitivity/

Extract: "The recent papers, by Kyle Armour (hereafter A17) and by us (Proistosescu and Huybers, 2017) (hereafter PH17), build on a large literature documenting the time-dependence of climate feedbacks in models. They make quantitative apples-to-apples comparisons between the climate sensitivities simulated by CMIP5 models and those inferred from global energy budget observations.

Because feedbacks may change over time as patterns of warming evolve, observations made today do not necessarily provide estimates of the long-term, equilibrium climate sensitivity (ECS). Rather, they constrain a quantity that we call the inferred (A17), or instantaneous (PH17), climate sensitivity (ICS). The two studies were performed independently using distinct methodologies, and both find that ICS values are systematically lower than ECS values within CMIP5 models. Moreover, they find that model-derived ICS values are consistent with ICS values inferred from observations.
…
What is the magnitude of ECS? (hint:≠ICS)
An important core finding of A17 and PH17 is that values of ICS drawn from the historical record are not sufficient to constrain values of ECS. Indeed, within models, ICS and ECS differ as the strength of radiative feedbacks change over time as patterns of surface temperature evolve with warming. PH17 demonstrated that portions of the climate system that respond over centennial timescales (such as the southern oceans) are important amplifiers of climate sensitivity in the models – a slow-mode response leading to values of ECS that are higher than the values of ICS that reflect more transient warming. Increasing sensitivity over time seems to be associated with a low-cloud feedback excited by warming in the Eastern Equatorial Pacific and Southern Ocean. This slow-mode response (and thus ECS) is essentially unconstrained by global energy budget observations because warming in these regions has been small, possibly held back by upwelling water from the ocean interior.

Key research targets should be improving understanding of (i) how the east-west temperature gradient in the Pacific Ocean will evolve in the future, and (ii) how low-level cloud (and other) feedbacks will respond, in turn. Zhou et al (2017) suggest that feedbacks can vary with the surface warming pattern, at least on decadal timescales."

[AbruptSLR]

As the Greenland Ice Sheet is currently losing ice mass faster than Antarctica, and will likely do so for next few decades, the linked reference is relevant over that timeframe.  And it finds that freshwater hosing into the North Atlantic in their model both increased surface warming in the Southern Hemisphere (which would help to destabilize the WAIS in the next few decades); and increased positive feedback related to clouds in the tropics.  Both of these findings agree with Hansen's ice-climate feedback mechanism.  Finally, I note that AR5/CMIP5 does not include this freshwater hosing mechanism:

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."

[Daniel B.]

As the Greenland Ice Sheet is currently losing ice mass faster than Antarctica, and will likely do so for next few decades, the linked reference is relevant over that timeframe.  And it finds that freshwater hosing into the North Atlantic in their model both increased surface warming in the Southern Hemisphere (which would help to destabilize the WAIS in the next few decades); and increased positive feedback related to clouds in the tropics.  Both of these findings agree with Hansen's ice-climate feedback mechanism.  Finally, I note that AR5/CMIP5 does not include this freshwater hosing mechanism:

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."

How does this year's large mass gain in Greenland affect this conclusion?

[jai mitchell]

How does this year's large mass gain in Greenland affect this conclusion?

you are falling into an easily avoided trap.  there is a reported value of 'surface mass balance' which looks at snowfall accumulation and melt.  However, this is not the total mass balance of the ice sheet, with about 4X more ancient glacier ice melting (mostly calving into the oceans) than has been accumulated by snow, this year total mass balance may be net zero, not growth.

http://www.climatecentral.org/news/despite-summer-snow-greenland-still-melting-21643

This year’s excess snowfall doesn’t mean that melt isn’t still happening, though. Melt has already picked back up since the last summer snow earlier this month, Box said. In fact, he expects that that snow will now be a layer of slush he’ll have to trudge through when he arrives on the ice sheet this week to check on a network of weather stations.

The snow could, however, balance out the year’s melt, Box said, with the ice sheet ending up with no net loss of ice for the year — the first year that will have happened in two decades.

One year without a net loss also doesn’t buck the long-term trend of Greenland losing ice, both from surface melt and from ocean waters eating away at glaciers that flow out to sea.

The increase in snowfall “is about four or five times smaller than the increase in surface melting,” Box said. So “the Greenland ice sheet is losing mass overall.”

[Daniel B.]

How does this year's large mass gain in Greenland affect this conclusion?

you are falling into an easily avoided trap.  there is a reported value of 'surface mass balance' which looks at snowfall accumulation and melt.  However, this is not the total mass balance of the ice sheet, with about 4X more ancient glacier ice melting (mostly calving into the oceans) than has been accumulated by snow, this year total mass balance may be net zero, not growth.

http://www.climatecentral.org/news/despite-summer-snow-greenland-still-melting-21643

This year’s excess snowfall doesn’t mean that melt isn’t still happening, though. Melt has already picked back up since the last summer snow earlier this month, Box said. In fact, he expects that that snow will now be a layer of slush he’ll have to trudge through when he arrives on the ice sheet this week to check on a network of weather stations.

The snow could, however, balance out the year’s melt, Box said, with the ice sheet ending up with no net loss of ice for the year — the first year that will have happened in two decades.

One year without a net loss also doesn’t buck the long-term trend of Greenland losing ice, both from surface melt and from ocean waters eating away at glaciers that flow out to sea.

The increase in snowfall “is about four or five times smaller than the increase in surface melting,” Box said. So “the Greenland ice sheet is losing mass overall.”

This is not a "trap."  Snow and melt happen every year.  This past winter's snow were quite excessive, and the summer melt (which appears to have ended) never picked up.   Consequently, Greenland is expected to post a net mass gain of ~500 Gt.  Yes, the ice sheet has been losing mass for a decade, this one year does not make up for past losses.  It may just be an anomaly.  However, dismissing it as erroneous is the bigger trap.

[Ned W]

[...]

Jai, hope you don't mind but there's a question that's been baffling me.   

In this post from another thread, you wrote:

early mortality projections, mainly in sub-sahara Africa  and SE Asia under a >2.0C warming scenario are in excess of 1 billion human beings.

Geoff Beacon asked for a source, and you replied with this:

http://apps.who.int/iris/bitstream/10665/134014/1/9789241507691_eng.pdf

    Climate change is projected to have substantial adverse impacts on future mortality, even
    under optimistic scenarios of future socioeconomic development. Under a base case
    socioeconomic scenario, we estimate approximately 250 000 additional deaths due to climate
    change per year between 2030 and 2050.

https://forum.arctic-sea-ice.net/index.php/topic,1920.msg108521.html#msg108521

Perhaps I'm missing something obvious, but I don't understand how you went from "250,000 additional deaths ... per year between 2030 and 2050" to "mortality projections ... are in excess of 1 billion human beings"  250,000 cases/year x 20 years is 5 million, not over 1 billion.

Was there some additional aspect that I'm missing?  Just curious.

[Daniel B.]

[...]

Jai, hope you don't mind but there's a question that's been baffling me.   

In this post from another thread, you wrote:

early mortality projections, mainly in sub-sahara Africa  and SE Asia under a >2.0C warming scenario are in excess of 1 billion human beings.

Geoff Beacon asked for a source, and you replied with this:

http://apps.who.int/iris/bitstream/10665/134014/1/9789241507691_eng.pdf

    Climate change is projected to have substantial adverse impacts on future mortality, even
    under optimistic scenarios of future socioeconomic development. Under a base case
    socioeconomic scenario, we estimate approximately 250 000 additional deaths due to climate
    change per year between 2030 and 2050.

https://forum.arctic-sea-ice.net/index.php/topic,1920.msg108521.html#msg108521

Perhaps I'm missing something obvious, but I don't understand how you went from "250,000 additional deaths ... per year between 2030 and 2050" to "mortality projections ... are in excess of 1 billion human beings"  250,000 cases/year x 20 years is 5 million, not over 1 billion.

Was there some additional aspect that I'm missing?  Just curious.

Maybe he meant over the next four millenia.

[AbruptSLR]

This is not a "trap."  Snow and melt happen every year.  This past winter's snow were quite excessive, and the summer melt (which appears to have ended) never picked up.   Consequently, Greenland is expected to post a net mass gain of ~500 Gt.  Yes, the ice sheet has been losing mass for a decade, this one year does not make up for past losses.  It may just be an anomaly.  However, dismissing it as erroneous is the bigger trap.

When considering climate change trend lines, one does not ignore the annular variability, but rather one uses a sufficiently large scale to see the trend from the variability (i.e. seeing the forest from the trees), as indicated by the data/image from the linked NASA website of GRACE satellite ice mass loss measurements in both Greenland and Antarctica:

https://climate.nasa.gov/vital-signs/land-ice/

[Ned W]

Maybe he meant over the next four millenia.

YMMV, but I'm not really comfortable forecasting mortality rates in the year 6029.  Guess I'm just one of those "conservative scientists" this thread is warning us all about.   

More likely there was some additional angle that I just didn't get.  But I do find the claim of 1 billion excess deaths a bit hard to believe. 

[Daniel B.]

This is not a "trap."  Snow and melt happen every year.  This past winter's snow were quite excessive, and the summer melt (which appears to have ended) never picked up.   Consequently, Greenland is expected to post a net mass gain of ~500 Gt.  Yes, the ice sheet has been losing mass for a decade, this one year does not make up for past losses.  It may just be an anomaly.  However, dismissing it as erroneous is the bigger trap.

When considering climate change trend lines, one does not ignore the annular variability, but rather one uses a sufficiently large scale to see the trend from the variability (i.e. seeing the forest from the trees), as indicated by the data/image from the linked NASA website of GRACE satellite ice mass loss measurements in both Greenland and Antarctica:

https://climate.nasa.gov/vital-signs/land-ice/

I agree that one should use a sufficiently large scale.  However, cherry picking that scale to show the maximum trend, does you no great service.  The net gain in the 30 years prior to the start of your posted graph was almost 1000 Gt.  Add that to this year's expected 500 Gt gain, and the trend over the past half century is only half that stated on your plot.  Potential ice loss from Greenland is a real concern.  However, we should strive to state the current situation as accurately as possible. 

[AbruptSLR]

I agree that one should use a sufficiently large scale.  However, cherry picking that scale to show the maximum trend, does you no great service.  The net gain in the 30 years prior to the start of your posted graph was almost 1000 Gt.  Add that to this year's expected 500 Gt gain, and the trend over the past half century is only half that stated on your plot.  Potential ice loss from Greenland is a real concern.  However, we should strive to state the current situation as accurately as possible.

Perhaps you should criticize NASA for the scales of the ice mass plots, and I think that you are doing yourself 'no great service', by implying that you believe that this plot will show a 500 Gt mass gain for Greenland by the end of 2017, as that is a ludicrous suggestion.  Provide a post of the linked NASA's GRACE plot a year from now and we will see who is being reasonable.

Edit: I hope that you are considering runoff in your evaluation of Greenland's net ice mass loss this year.

[AbruptSLR]

More likely there was some additional angle that I just didn't get.  But I do find the claim of 1 billion excess deaths a bit hard to believe.

While I cannot speak for jai, and while there is a lot of uncertainty in projecting human behavior; the first two attached images provide projections from the World3 model (see the linked pdf & the linked Wikipedia article) both showing model runs about 40-years after Limits to Growth was first published in the 1970's.  Both images show a normalized peak in population circa 2050.

Title: "40 years after Limits to Growth The World3 system dynamics model and its impacts"

http://www.wrforum.org/wp-content/uploads/2015/09/Limits-to-growth.pdf

&

https://en.wikipedia.org/wiki/World3

Extract: "At least one study, however, claims that "30 years of historical data compare favorably with key features of a business-as-usual scenario called the 'standard run' scenario" produced by the World3 model."

The third image shows the 2017 UN world population projection, which shows a projected median population of 9.8 billion people by 2050.  Thus if one applies this 9.8 billion median population by 2050 to the normalized World3 peak population circa 2050, it is easy to see that billions of people will likely die in the decades following 2050.

[Ned W]

That is not prticularly convincing on its own terms, ASLR, and it certainly has nothing to do with the methodology from the WHO white paper that Jai Mitchell was citing as the source for the claim of more than a billion excss deaths. 

The material you're bringing up is just output from a highly generalized system dynamics model.  During the retrospective period, it seems to have greatly overestimated death rates, which have fallen dramatically over the past few decades. 

Some would say that choosing to ignore the much more detailed work of the WHO on mortality rates, and instead relying on the highly abstract and non-empirically grounded output of a systems dynamics model, would be "erring on the side of maximum drama" but YMMV, I suppose.

[AbruptSLR]

... relying on the highly abstract and non-empirically grounded output of a systems dynamics model, would be "erring on the side of maximum drama" but YMMV, I suppose.

The UN and other such organization do not consider worst case risk assessments; which does not mean that they may not happen.

[AbruptSLR]

The first linked article entitled: "Investigating the Enigma of Clouds and Climate Change", indicates that net cloud feedback is more positive than previously assumed as satellite data confirms that with warming, clouds are both moving higher and pole-ward.

http://e360.yale.edu/features/investigating-the-enigma-of-clouds-and-climate-change

Extract: "In an interview with Yale Environment 360, Marvel discusses what is known about the behavior of clouds in a warming world (they are migrating more toward the poles), explains why strict controls need to be imposed on geoengineering experiments with clouds …
..
e360: What are the consequences of this poleward and upward motion of clouds?

Marvel: Both of them give rise to what I think is the most confusing part of climate jargon. We call it a positive feedback, and you think “positive feedback” — that sounds great. I like getting positive feedback. But when climate scientists talk about a positive feedback, we mean some process that changes in response to warming, that accelerates that warming. So both of those changes are what we would call a positive feedback, meaning it enhances the warming.
…
Marvel: People ask me, “Aren’t you just depressed all the time? How do you keep going in the face of this?” We’re all going to die. You know, there’s not a lot of good news there. But we all manage to find happiness and fun in our lives anyway. And I do have hope, I do think that we are an amazing species; and we do a lot of terrible things, but we also do a lot of very good things. I do have hope in human ingenuity."

The second linked reference provides satellite data (see the attached image) from CloudSat & CALIPSO within the A-Train, that show a dramatic increase (more positive) in observed net cloud feedback as compared to prior assumptions.  This of course means that ECS is higher than previously assumed.

Graeme Stephens et. al. (2017), "CloudSat and CALIPSO within the A-Train: Ten years of actively observing the Earth system", BAMS, https://doi.org/10.1175/BAMS-D-16-0324.1

http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-16-0324.1?utm_content=bufferebbb9&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer
or
http://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-16-0324.1

Abstract: "The more than 10 years of observations jointly collected by CloudSat and CALIPSO satellites has resulted in new ways of looking at aerosol, clouds, and precipitation and new discoveries about processes that connect them.

One of the most successful demonstrations of an integrated approach to observe Earth from multiple perspectives is the A-Train satellite constellation (e.g. Stephens et al., 2002). The science enabled by this constellation flourished with the introduction of the two active sensors carried by the NASA CloudSat and the NASA/CNES Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellites that were launched together on April 28th, 2006. These two missions have provided a 10-year demonstration of coordinated formation flying that made it possible to develop integrated products and that offered new insights on key atmospheric processes. The progress achieved over this decade of observations, summarized in this paper, clearly demonstrate the fundamental importance of the vertical structure of clouds and aerosol for understanding the influences of the larger scale atmospheric circulation on aerosol, the hydrological cycle, the cloud-scale physics and on the formation of the major storm systems of Earth. The research also underscored inherent ambiguities in radiance data in describing cloud properties and how these active systems have greatly enhanced passive observation. It is now clear that monitoring the vertical structure of clouds and aerosol is essential and a climate data record is now being constructed. These pioneering efforts are to be continued with EarthCARE mission planned for launch in 2019."

Caption: "Figure 5 Upper three panels are from Hartmann et al (1992) who estimate the contribution to the cloud radiative effects (CRE) of five classes of clouds as defined according to the ISCCP radiance classification (upper left). The bottom panels are the equivalent analysis but with classification determined by the radar-lidar data of CloudSat and CALIPSO where true cloud heights establish the types and cloud thickness (x axis) are from water and ice path information which is proportional to cloud optical depth. The differences in CRE between this latter analysis and that of Hartmann et al underscores the effects of misclassification of clouds on the interpretation of their radiative effects. Ci=cirrus, D.C.=Deep Convection, M.L.=multi-layer, AS=Altostratus, AC-Alto-cumulus, NS=Nimbostratus, St=stratus, SC=stratocumulus and Cu=cumulus."

Note: I added bold font to the Kate Marvel interview for emphasis

[AbruptSLR]

The linked MAHB website offers numerous & multi-disciplinary articles regarding the reality of the challenges that mankind and the biosphere are currently facing in the Anthropocene.  In this regards, I also provide a link to the MAHB archive on extinction as well as three links to the most recent articles on the website, including to one entitled "When optimism spells disaster…", that emphasizes that the cure to human stupidity is wisdom:

The Millennium Alliance for Humanity and the Biosphere: connecting activists, scientists, humanists and civil society to foster global change.

https://mahb.stanford.edu/

https://mahb.stanford.edu/library-category/extinction/

Title: "When optimism spells disaster…"

https://mahb.stanford.edu/blog/optimism/

Extract: "One of the most dangerous threats to the human future in this, the Age of Perils, is … optimism.

Nowadays, if you tell the tested truth about climate science, weapons of mass destruction, global pollution, extinction or, indeed, any of the ten existential threats now closing in on humanity, you are likely to provoke one of two responses.

The first is a sober “Shit. I never knew it was that bad. What’s the evidence?” followed by “What can we do about it?”

The second ranges from polite dismissal to “I don’t want to hear all that bad news”, to outright, hysterical abuse, in which you are labelled everything from a “doomsayer” and a “Malthusian” to a spreader of lies, a “greenie nutcase” or even a socialist, a Marxist or a contemptible liberal!

Human society neatly divides into folk who can handle bad news – and those who can’t. Those who put their hands over their ears and demand you shut up. Or, as Charles Darwin might have observed, those who are fit for survival – and those who ain’t.
…
Optimism can be a useful attribute in a general, a politician or a business manager, providing it is based on fact, not mere belief. It nurtures the resilience to endure tough times. But remaining stubbornly “optimistic” when the weight of evidence points to imminent dangers to civilization and maybe even our species is a formula for disaster, that spells inaction and, consequently, an increase in the scale of the risk. It decreases our fitness for survival. It is, in short, extremely unwise.

Many “optimists” insist that humans are so smart we will come up with technical solutions to all the leading threats we face (though how we can do this with nuclear weapons is a moot question). And it is true that technical solutions exist to most of them. However, this ignores the fact that many of our greatest institutions – governments, corporations, faiths – are unable or unwilling to take action until the threats become so vast as to be unstoppable. The technical solutions will not develop unless society sees a need for them.

In this case it is the blind optimists, rather than the realistic pessimists, who imperil our future.
..
To overcome them humanity doesn’t need optimism or pessimism. It needs to exercise a singular attribute that has stood us in good stead for over a million years: wisdom."


&

Title: "When and How Will Growth Cease?"

https://mahb.stanford.edu/blog/when-how-growth-cease/

&

Title: "Contraceptual Art"

https://mahb.stanford.edu/creative-expressions/contraceptual-art/

[AbruptSLR]

The linked article is by BBC Future, and indicates that some experts believe the human society is politically and psychologically incapable of adequately addressing climate problems this century:

Title: "How Western civilization could collapse"

http://www.bbc.com/future/story/20170418-how-western-civilisation-could-collapse

Extract: "Unfortunately, some experts believe such tough decisions exceed our political and psychological capabilities. “The world will not rise to the occasion of solving the climate problem during this century, simply because it is more expensive in the short term to solve the problem than it is to just keep acting as usual,” says Jorgen Randers, a professor emeritus of climate strategy at the BI Norwegian Business School, and author of 2052: A Global Forecast for the Next Forty Years. “The climate problem will get worse and worse and worse because we won’t be able to live up to what we’ve promised to do in the Paris Agreement and elsewhere.”

See also:

Title: "2052: A Global Forecast for the Next Forty Years"

https://www.amazon.com/dp/B008674K64/ref=dp-kindle-redirect?_encoding=UTF8&btkr=1

Extract: "Forty years ago, The Limits to Growth study addressed the grand question of how humans would adapt to the physical limitations of planet Earth. It predicted that during the first half of the 21st century the ongoing growth in the human ecological footprint would stop-either through catastrophic "overshoot and collapse"-or through well-managed "peak and decline."

So, where are we now? And what does our future look like?  In the book 2052, Jorgen Randers, one of the coauthors of Limits to Growth, issues a progress report and makes a forecast for the next forty years. To do this, he asked dozens of experts to weigh in with their best predictions on how our economies, energy supplies, natural resources, climate, food, fisheries, militaries, political divisions, cities, psyches, and more will take shape in the coming decades. He then synthesized those scenarios into a global forecast of life as we will most likely know it in the years ahead.

The good news: we will see impressive advances in resource efficiency, and an increasing focus on human well-being rather than on per capita income growth. But this change might not come as we expect. Future growth in population and GDP, for instance, will be constrained in surprising ways-by rapid fertility decline as result of increased urbanization, productivity decline as a result of social unrest, and continuing poverty among the poorest 2 billion world citizens. Runaway global warming, too, is likely.

So, how do we prepare for the years ahead? With heart, fact, and wisdom, Randers guides us along a realistic path into the future and discusses what readers can do to ensure a better life for themselves and their children during the increasing turmoil of the next forty years."

[AbruptSLR]

Per the linked study, under the right combination of events, a societal collapse is possible as early as 2030:

http://www3.weforum.org/docs/WEF_FutureRoleCivilSociety_Report_2013.pdf

See also:

Title: "Nasa-funded study: industrial civilisation headed for 'irreversible collapse'?"

https://www.theguardian.com/environment/earth-insight/2014/mar/14/nasa-civilisation-irreversible-collapse-study-scientists

Extract: "Although the study based on HANDY is largely theoretical - a 'thought-experiment' - a number of other more empirically-focused studies - by KPMG and the UK Government Office of Science for instance - have warned that the convergence of food, water and energy crises could create a 'perfect storm' within about fifteen years. But these 'business as usual' forecasts could be very conservative."

[Daniel B.]

Per the linked study, under the right combination of events, a societal collapse is possible as early as 2030:

http://www3.weforum.org/docs/WEF_FutureRoleCivilSociety_Report_2013.pdf

See also:

Title: "Nasa-funded study: industrial civilisation headed for 'irreversible collapse'?"

https://www.theguardian.com/environment/earth-insight/2014/mar/14/nasa-civilisation-irreversible-collapse-study-scientists

Extract: "Although the study based on HANDY is largely theoretical - a 'thought-experiment' - a number of other more empirically-focused studies - by KPMG and the UK Government Office of Science for instance - have warned that the convergence of food, water and energy crises could create a 'perfect storm' within about fifteen years. But these 'business as usual' forecasts could be very conservative."

You seem to be taking the most negative approach possible.  While anything is possible (even the societal collapse you claim), the linked report makes no such claim.  Rather, the report highlighted the challenges society is expected to face in the coming decades.  Climate change was not one of the highest rated challenges expected.

[TerryM]

You seem to be taking the most negative approach possible.  While anything is possible (even the societal collapse you claim), the linked report makes no such claim.  Rather, the report highlighted the challenges society is expected to face in the coming decades.  Climate change was not one of the highest rated challenges expected.

Now that really is scary.

Terry

[AbruptSLR]

You seem to be taking the most negative approach possible.  While anything is possible (even the societal collapse you claim), the linked report makes no such claim.  Rather, the report highlighted the challenges society is expected to face in the coming decades.  Climate change was not one of the highest rated challenges expected.

You seem to be looking for a Savior that will absolve you of any responsibility yourself.  A Savior that will provide you with dogma that will tell you what to expect every single day.

You need to realize that PDFs change continuously (e.g. the election of Donald Trump was unexpected but it increases the probability of climate change catastrophe; or that the failure to implement Kyoto also dramatically increased the probability of climate change catastrophe); and the fact that a study a few years ago gave climate change a lower risk evaluation is irrelevant.  In any event, this line of discussion belongs in the "Human Stupidity (Human Mental Illness)" thread; so if you want to discuss how climate change can act as a stress riser that progressively increases the probability of societal collapse with every year that it is not effectively dealt with then you can either move your comments over there, and/or you can do your own research on how the US military evaluates climate change as a stress riser.

Edit: One of the primary focuses of this thread is how AR5 underestimates Equilibrium Climate Sensitivity, ECS; which is yet another very important example of how publish peer reviewed PDFs for climate change risk can shift to the right thereby increasing the importance of climate change as a stress riser for socio-economic collapse.  For example, Proistosescu & Huybers (2017) essentially prove that CMIP5 indicates that AR5 should have assumed (for policy advise) a median value for ECS of about 3.5C instead of about 3C; while this thread shows that CMIP5 errs on the side of least drama, to the point that I suspect that CMIP6 will indicate a median value for ECS of 4C; and that CMIP7 may indicate a median value for ECS between 4 and 4.5C.

Edit 2: As another example of how probability density functions can shift to the right, the attached image of the 2015 UN World Population Projection gives a median world population of about 9.6 billion by 2050, while the 2017 value given in Reply #1816 is 9.8 billion for 2050.  The increased consumption by these additional people increases the rise of societal collapse from what was assumed earlier; and I would not be surprised if the UN's projections for world population continue to increase as the 4th Industrial Revolution postpones the date of potential societal collapse when the population may well drop rapidly.

[Daniel B.]

You seem to be taking the most negative approach possible.  While anything is possible (even the societal collapse you claim), the linked report makes no such claim.  Rather, the report highlighted the challenges society is expected to face in the coming decades.  Climate change was not one of the highest rated challenges expected.

You seem to be looking for a Savior that will absolve you of any responsibility yourself.  A Savior that will provide you with dogma that will tell you what to expect every single day.

You need to realize that PDFs change continuously (e.g. the election of Donald Trump was unexpected but it increases the probability of climate change catastrophe; or that the failure to implement Kyoto also dramatically increased the probability of climate change catastrophe); and the fact that a study a few years ago gave climate change a lower risk evaluation is irrelevant.  In any event, this line of discussion belongs in the "Human Stupidity (Human Mental Illness)" thread; so if you want to discuss how climate change can act as a stress riser that progressively increases the probability of societal collapse with every year that it is not effectively dealt with then you can either move your comments over there, and/or you can do your own research on how the US military evaluates climate change as a stress riser.

Edit: One of the primary focuses of this thread is how AR5 underestimates Equilibrium Climate Sensitivity; which is yet another very important example of how publish peer reviewed PDFs for climate change risk can shift to the right thereby increasing the importance of climate change as a stress riser for socio-economic collapse.

AR5 only underestimates climate sensitivity if it is higher than the published range.  Their likely range of 1.5-4.5, and very likely range of 1-6 does not appear to underestimate the sensitivity.  Rather, they appear to overestimate the sensitivity, if anything. 
Masters, 2013, has one of the higher ranges for likely (1.5-2.9) and very likely (1.2-5.1), but even these are lower than the published AR5 numbers. 

https://rd.springer.com/article/10.1007/s00382-013-1770-4

Other papers think even these are too high.

http://onlinelibrary.wiley.com/doi/10.1002/2015EA000154/full

I am looking for a "Savior."  Rather, I am looking for truth and accuracy.  I do not consider highly unlikely, worst case scenarios as possible outcomes.  Especially when the uncertainty in such predictions are so high.  Call me a conservative scientist all you like, but until you can show me otherwise, I will side with the most likely scientific outcome.  Granted, outcomes could be higher (or lower), but history has shown that these possibilities do not materialize.  Thus far, climate change has not increased societal stress.  The fear of climate catastrophe has had a much larger impact.  I will not contribute to these fears.

[AbruptSLR]

I am looking for a "Savior."  Rather, I am looking for truth and accuracy.

If you are looking for truth and accuracy you would do well by at least quoting research published after AR5 rather than prior to it; and some of this more recent research can be found in this thread (if you care to review it)..As a starting point, I selected the following 28 references [not including Proistosescu & Huybers (2017)] that either directly, or indirectly, indicate that climate sensitivity is most likely significantly higher than the range summarized by AR5:

1. The linked reference analyses the CMIP3&5 results to conclude the ECS is likely 3.9C +/- 0.45C:

Chengxing Zhai, Jonathan H. Jiang & Hui Su (2015), "Long-term cloud change imprinted in seasonal cloud variation: More evidence of high climate sensitivity", Geophysical Research Letters, DOI: 10.1002/2015GL065911


http://onlinelibrary.wiley.com/doi/10.1002/2015GL065911/full

2. The linked reference provides findings from CMIP5 of the continued poleward expansion of the Hadley Cell with continued global warming; which in-turn supports the idea that ECS is greater than 3C:

Lijun Tao, Yongyun Hu & Jiping Liu (May 2016), "Anthropogenic forcing on the Hadley circulation in CMIP5 simulations", Climate Dynamics, Volume 46, Issue 9, pp 3337-3350 DOI: 10.1007/s00382-015-2772-1

http://rd.springer.com/article/10.1007%2Fs00382-015-2772-1

3. The linked reference presents new paleo evidence about the Eocene.  While the authors emphasize that their findings support the IPCC interpretation for climate sensitivity, when looking at the attached Fig 4 panel f, it appears to me that this is only the case if one averages ECS over the entire Eocene; while if one focuses on the Early Eocene Climate Optimum (EECO) which CO₂ levels were higher than in current modern times, it appear that ECS was higher (around 4C) than the IPCC AR5 assumes (considering that we are increasing CO2 concentrations faster now that during the EECO this gives me concern rather than reassurance).

Eleni Anagnostou, Eleanor H. John, Kirsty M. Edgar, Gavin L. Foster, Andy Ridgwell, Gordon N. Inglis, Richard D. Pancost, Daniel J. Lunt & Paul N. Pearson (2016), "Changing atmospheric CO2 concentration was the primary driver of early Cenozoic climate", Nature, doi:10.1038/nature17423


http://www.nature.com/nature/journal/vaop/ncurrent/full/nature17423.html

4. Tan et al (2016) indicates that ECS may well be between 5.0 and 5.3C.

Ivy Tan, Trude Storelvmo & Mark D. Zelinka (08 Apr 2016), "Observational constraints on mixed-phase clouds imply higher climate sensitivity", Science, Vol. 352, Issue 6282, pp. 224-227, DOI: 10.1126/science.aad5300


http://science.sciencemag.org/content/352/6282/224

5. According to the IPCC AR5 report: "The transient climate response is likely in the range of 1.0°C to 2.5°C (high confidence) and extremely unlikely greater than 3°C"; however, the linked reference uses only observed data to indicate that TCR is 2.0 +/- 0.8C.  Thus AR5 has once again erred on the side of least drama.


T. Storelvmo, T. Leirvik, U. Lohmann, P. C. B. Phillips & M. Wild (2016), "Disentangling greenhouse warming and aerosol cooling to reveal Earth’s climate sensitivity", Nature Geoscience, doi:10.1038/ngeo2670


http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2670.html

6. The linked reference reassesses ECS from CMIP3 &5 and find an ensemble-mean of 3.9C, and I note that CMIP3&5 likely err on the side of least drama as they ignore several important non-linear slow feedbacks that could be accelerated by global warming:

Chengxing Zhai, Jonathan H. Jiang, Hui Su (2015), "Long-term cloud change imprinted in seasonal cloud variation: More evidence of high climate sensitivity", Geophysical Research Letters, DOI: 10.1002/2015GL065911

http://onlinelibrary.wiley.com/doi/10.1002/2015GL065911/full

7. The linked reference could not make it more clear that paleo-evidence from inter-glacial periods indicates that ECS is meaningfully higher than 3C and that climate models are commonly under predicting the magnitude of coming climate change.

Dana L. Royer (2016), "Climate Sensitivity in the Geologic Past", Annual Review of Earth and Planetary Sciences, Vol. 44


http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-100815-024150?src=recsys

8. Thompson indicates that ECS has a 95%CL range of from 3C to 6.3C, with a best estimate of 4C, and Sherwood (2014) has a higher value still:

Climate sensitivity by Roy Thompson published by Earth and Environmental Science Transactions of the Royal Society of Edinburgh, DOI: 10.1017/S1755691015000213

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10061758&fileId=S1755691015000213


9. Tian (2015) indicates that the double-ITCZ bias constrains ECS to its high end (around 4.0C):

Tian, B. (2015), "Spread of model climate sensitivity linked to double-Intertropical Convergence Zone bias", Geophys. Res. Lett., 42, doi:10.1002/2015GL064119.


http://onlinelibrary.wiley.com/doi/10.1002/2015GL064119/abstract

10. Sherwood et al (2014), which found that ECS cannot be less than 3C, and is likely currently in the 4.1C range.  Also, everyone should remember that the effective ECS is not a constant, and models project that following a BAU pathway will result in the effective ECS increasing this century:


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

11. The linked reference studies numerous climate models and finds that: "… those that simulate the present-day climate best even point to a best estimate of ECS in the range of 3–4.5°C."
Reto Knutti, Maria A. A. Rugenstein (2015), "Feedbacks, climate sensitivity and the limits of linear models", Philosophical Transactions of the Royal Society A, DOI: 10.1098/rsta.2015.0146

http://rsta.royalsocietypublishing.org/content/373/2054/20150146

12.  The linked reference indicates that the cloud feedback from tropical land is robustly positive.  As AR5 did not know whether this contribution to climate sensitivity was positive or negative, this clearly indicates that AR5 errs on the side of least drama with regard to both TCR & ECS:

Youichi Kamae, Tomoo Ogura, Masahiro Watanabe, Shang-Ping Xie and Hiroaki Ueda (8 March 2016), "Robust cloud feedback over tropical land in a warming climate", Atmospheres, DOI: 10.1002/2015JD024525

http://onlinelibrary.wiley.com/doi/10.1002/2015JD024525/abstract

13.  Graeme L. Stephens, Brian H. Kahn and Mark Richardson (5 May, 2016), "The Super Greenhouse effect in a changing climate", Journal of Climate, DOI: http://dx.doi.org/10.1175/JCLI-D-15-0234.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0234.1

14. The linked reference assumes different degrees of nonlinearity for climate feedback mechanisms and concludes that such nonlinearity for positive feedback represents a Black Swan risk that linear climate models cannot recognize:

Jonah Bloch-Johnson, Raymond T. Pierrehumbert & Dorian S. Abbot (24 June 2015), "Feedback temperature dependence determines the risk of high warming", Geophysical Research Letters, DOI: 10.1002/2015GL064240

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064240/full


15.  While the linked (open access) reference has many appropriate qualifying statements and disclaimers, it notes that the AR5 paleo estimates of ECS were linear approximations that change when non-linear issues are considered.  In particular the find for the specific ECS, S[CO2,LI], during the Pleistocence (ie the most recent 2 million years) that:
"During Pleistocene intermediate glaciated climates and interglacial periods, S[CO2,LI] is on average ~ 45 % larger than during Pleistocene full glacial conditions."

Therefore, researchers such as James Hansen who relied on paleo findings that during recent full glacial periods ECS was about 3.0C, did not know that during interglacial periods this value would be 45% larger, or 4.35C.

Köhler, P., de Boer, B., von der Heydt, A. S., Stap, L. B., and van de Wal, R. S. W. (2015), "On the state dependency of the equilibrium climate sensitivity during the last 5 million years", Clim. Past, 11, 1801-1823, doi:10.5194/cp-11-1801-2015.


http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.html
http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.pdf

16.  The linked reference implies that climate sensitivity (ESS) could be much higher than previously assumed:

Jagniecki,Elliot A. et al. (2015), "Eocene atmospheric CO2from the nahcolite proxy", Geology, http://dx.doi.org/10.1130/G36886.1


http://geology.gsapubs.org/content/early/2015/10/23/G36886.1

17.  The linked open access reference identifies three constraints on low cloud formation that suggest that cloud feedback is more positive than previously thought.  If verified this would mean that both TCR and ECS (and ESS) are larger than previously thought:

Stephen A. Klein and Alex Hall (26 October 2015), "Emergent Constraints for Cloud Feedbacks", Climate Feedbacks (M Zelinka, Section Editor), Current Climate Change Reports, pp 1-12, DOI 10.1007/s40641-015-0027-1

http://link.springer.com/article/10.1007%2Fs40641-015-0027-1

18.  The linked article indicates that values of TCR based on observed climate change are likely underestimated:

J. M. Gregory, T. Andrews and P. Good (5 October 2015), "The inconstancy of the transient climate response parameter under increasing CO₂", Philosophical Transactions of the Royal Society A, DOI: 10.1098/rsta.2014.0417


http://rsta.royalsocietypublishing.org/content/373/2054/20140417

19.  The linked reference indicates that most current climate models underestimate climate sensitivity:

J. T. Fasullo, B. M. Sanderson & K. E. Trenberth (2015), "Recent Progress in Constraining Climate Sensitivity With Model Ensembles", Current Climate Change Reports, Volume 1, Issue 4, pp 268-275, DOI 10.1007/s40641-015-0021-7

http://link.springer.com/article/10.1007/s40641-015-0021-7?wt_mc=email.event.1.SEM.ArticleAuthorOnlineFirst

20.  The linked reference indicates that studies that assuming linearity of climate sensitivity likely underestimate the risk of high warming.

Jonah Bloch-Johnson, Raymond T. Pierrehumbert and Dorian S. Abbot (June 2015), "Feedback temperature dependence determines the risk of high warming", Geophysical Research Letters, DOI: 10.1002/2015GL064240

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064240/abstract

21. The linked reference indicates that new research (from PlioMIP2) demonstrates that the climate sensitivity for the Pliocene was higher than previously believed (from PlioMIP1):

Kamae, Y., Yoshida, K., and Ueda, H.: Sensitivity of Pliocene climate simulations in MRI-CGCM2.3 to respective boundary conditions, Clim. Past, 12, 1619-1634, doi:10.5194/cp-12-1619-2016, 2016.

http://www.clim-past.net/12/1619/2016/

http://www.clim-past.net/12/1619/2016/cp-12-1619-2016.pdf


22. The linked reference indicates that corrected recent observations indicate that the most likely value of ECS may be as high as 4.6C (see attached plot of the time dependent curve):

Kyle C. Armour  (27 June 2016), "Projection and prediction: Climate sensitivity on the rise", Nature Climate Change, doi:10.1038/nclimate3079

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3079.html

23. The linked reference indicates that the climate responses (climate sensitivities) projected by advanced climate models generally match observations when apple to apple comparisons are made.  This is a useful finding as advanced climate models generally indicate that climate sensitivity values are towards the high end of the IPCC climate sensitivity range:

Mark Richardson, Kevin Cowtan, Ed Hawkins & Martin B. Stolpe (2016), "Reconciled climate response estimates from climate models and the energy budget of Earth", Nature Climate Change, doi:10.1038/nclimate3066

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3066.html

24. The linked reference discusses paleodata to indicate that climate sensitivity increased from 3.3 - 5.6 (mean of 4.45k) at the beginning of the PETM up to 3.7 - 6.5 K (mean of 5.1K) near the peak of the PETM; and that if we burn only the easily accessible carbon reserves then GMST could increase by about 10C.  I note these climate sensitivity values are much higher than those inherent in the CMIP5 projections:

Gary Shaffer, Matthew Huber, Roberto Rondanelli & Jens Olaf Pepke Pedersen (23 June 2016), "Deep-time evidence for climate sensitivity increase with warming", Geophysical Research Letters, DOI: 10.1002/2016GL069243

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069243/full


25. The linked Reuters article notes that NASA reported that a new satellite-based method have located 39 unreported sources of anthropogenic emissions that, when accounted for, increase our previously estimated amount of sulfur dioxide by about 12 percent of all such anthropogenic emissions from 2005 to 2014.  This indicates that the CMIP5 projections also underestimated the impact of this negative forcing source; which raises the prospect that climate sensitivity (ECS) is likely higher than the CMIP5 models indicate, and the linked Zhai et al (2015) reference analyses of the CMIP3&5 results conclude that the ECS is likely 3.9C +/- 0.45C:

Chengxing Zhai, Jonathan H. Jiang & Hui Su (2015), "Long-term cloud change imprinted in seasonal cloud variation: More evidence of high climate sensitivity", Geophysical Research Letters, DOI: 10.1002/2015GL065911

http://in.reuters.com/article/us-nasa-pollution-idINKCN0YO1PW

26. The linked reference uses an information-theoretic weighting of climate models by how well they reproduce the satellite measured deseasonlized covariance of shortwave cloud reflection, indicates a most likely value of ECS of 4.0C; which indicates that AR5 errs on the side of least drama:

Florent Brient & Tapio Schneider (2016), "Constraints on climate sensitivity from space-based measurements of low-cloud reflection", Journal of Climate, DOI: http://dx.doi.org/10.1175/JCLI-D-15-0897.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0897.1


27. The linked article indicates that the contribution of sea-ice loss to Arctic Amplification is regulated by the PDO and that in positive PDO phases (like we are in now) there should be less Arctic Amplification.  Thus the fact that we are currently experiencing high Arctic Amplification during a period of highly positive PDO values gives cause for concern that climate sensitivity may be higher than considered by AR5:

James A. Screen & Jennifer A. Francis (2016), "Contribution of sea-ice loss to Arctic amplification is regulated by Pacific Ocean decadal variability", Nature Climate Change, DOI: 10.1038/nclimate3011


http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3011.html


28. The linked reference uses an information-theoretic weighting of climate models by how well they reproduce the satellite measured deseasonlized covariance of shortwave cloud reflection, indicates a most likely value of ECS of 4.0C.  As this satellite data is certainly biased by the recent acceleration of natural aerosol emissions associated with the increasing atmospheric CO2 concentration, the actually ECS is likely higher than 4.0C, as will become apparent if climate change reduces future plant activity.  Unfortunately, the envisioned upgrades to the Paris Pact do not have any contingency for addressing such high values (4 to 4.5C) of ECS (including accelerting NET):

Florent Brient & Tapio Schneider (2016), "Constraints on climate sensitivity from space-based measurements of low-cloud reflection", Journal of Climate, DOI: http://dx.doi.org/10.1175/JCLI-D-15-0897.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0897.1

And for those who do not like to read, I provide the two attached images of high equilibrium climate sensitivity, with the first based on paleo data, and the second based on modern observations.

[AbruptSLR]

Furthermore, the following summarizes selected considerations [including: (1) transient masking factors, (2) misinterpretations of paleo & observed climate sensitivities, (3) misinterpretations of the stability of the WAIS and (4) underestimates of the likeliness of continued high anthropogenic radiative forcing] as to why our climate change situation is more dire than the IPCC AR5 consensus (which represents scientism)  currently acknowledges:

1. Masking mechanisms which allow scientists to match model results to paleo & observed conditions while calibrating for relatively low climate response (while either ignoring many masking mechanisms [such as paleo-dust & paleo-SOA], or diminishing their effectiveness in the models); and which allow decision makers to procrastinate in exactly the timeframe when it was critical that they take immediate action. 

Hodzic, A., Kasibhatla, P. S., Jo, D. S., Cappa, C. D., Jimenez, J. L., Madronich, S., and Park, R. J.: Rethinking the global secondary organic aerosol (SOA) budget: stronger production, faster removal, shorter lifetime, Atmos. Chem. Phys., 16, 7917-7941, doi:10.5194/acp-16-7917-2016, 2016.

http://www.atmos-chem-phys.net/16/7917/2016/

W.R.T. GMSTA: Specific masking mechanisms include:

(a) Temporary (observed at least from roughly 1998 to 2013) atmospheric conditions in the Tropical Pacific that not only temporarily increased the frequency of lower level cloud cover with negative feedback, but also above average La Nina-like conditions and generally negative PDO values; which, accelerated the sequestration of heat in the ocean, which was partially release during the 2015-16 El Nino. 

(b) The temporary acceleration of anthropogenic aerosol emissions (largely associated with coal-fired power plants in both in China and elsewhere) that temporarily induced both negative forcing & negative feedback.

(c) A temporary acceleration of the absorption of carbon dioxide by land-based plants associate both with higher atmospheric carbon dioxide concentrations, and with global warming.

i. Keenan et. al. (2016) "Recent pause in the growth rate of atmospheric CO₂ due to enhanced terrestrial carbon uptake", Nature Communication, doi:10.1038/ncomms13428.

http://www.nature.com/articles/ncomms13428

Erik Hans Hoffmann, Andreas Tilgner, Roland Schrödner, Peter Bräuer, Ralf Wolke and Hartmut Herrmann (November 2016), "An advanced modeling study on the impacts and atmospheric implications of multiphase dimethyl sulfide chemistry", PNAS, vol. 113 no. 42,  11776–11781, doi: 10.1073/pnas.1606320113

http://www.pnas.org/content/113/42/11776

(d) Decadal scale thermal inertia fluctuations associated the ocean, atmosphere and cryosphere.
 
(f) A probable underestimation of both natural and anthropogenic negative aerosol forcing and feedback.

W.R.T. SLR: Specific masking consideration include:

(a) The tidal gauges around the world are located so as to be biased against the Greenland Ice Sheet, GIS, fingerprint contribution, likely underestimating SLR;

(b) In 2011 atypical atmospheric river event deposited large quantities of snow in Eastern Antarctica, thus underestimating SLR trends.

(c) Isostatic rebound associate with ice mass loss in the WAIS can mask the true ice mass loss measured by either gravity (GRACE) or ice surface elevation.

(d) If the WAIS is a major contributor to SLR this century, then due to the fingerprint effect this contribution could be increased by up to 40% in the NH.

W.R.T. Anthropogenic Bias: Other masking issues relate to the phrase "To err is human" in that AR5's projections contain so many caveats that it obfuscates the seriousness of our climate change challenge.  Specific anthropogenic masking factors include:

(a) The referenced standards for reporting observed GMST have been demonstrated to be biased on the low side.

(b) Anthropogenic forcing began earlier than assumed in AR5. 

(c) Common use of old values for GMSTA above pre-industrial.

(d) Common use radiative forcing scenarios that err too far on the side of least drama.

(e) Focus on linear Frequentist theory thereby underreporting the findings of chaos theory, of Bayesian analysis; of non-linear theory and of preliminary research that does yet meet the Frequentist confidence levels for evidence.

(f) Organized intimidation of climate scientists by denialists have contributed to ESLD reporting.

2. The TCR, ECS and ESS are all likely higher than consensus science is willing to currently acknowledge, due to a combination of:

(a) Masking factors biasing the recent observed climate change. 

(b) A misinterpretation of paleo-data with regard both the role of negative forcing from paleo dust and the role of Lorenz strange attractors in progressively ratcheting Earth Systems into higher states (such as an early albedo flip for the Arctic; and increased frequencies for strong El Nino events).

(c) The synergistic acceleration of non-liner positive feedback mechanisms (including Polar Amplification and permafrost degradation).

3. Instability of the WAIS could lead to a rapid acceleration of Hansen's ice-climate feedback mechanism within coming decades.  The likely earlier than expected collapse of key portions of the WAIS are due to reasons such as:

(a) The formation of the ozone hole over Antarctica accelerated the westerly winds over the Southern Ocean that together with the Coriolis effect drove warm circumpolar deep water, CDW, to the exposed ice of many key marine glaciers and associated ice shelves.

(b) The likelihood that GMSTA will approach (or exceed) 2.7C above pre-industrial conditions which per DeConto (2016) should trigger hydrofracturing and cliff failures of key WAIS marine glaciers.

(c) The rapid ocean heat uptake by the Southern Ocean's CDW (which is partially related to a climate change related increase in intense ENSO events).

4.  Anthropogenic radiative forcing would continue at higher than advisable levels, and for a longer than expected periods, due to such trends as:

(a) The transfer of industry from first world to third world countries (thus allowing high emissions to continue for some decades to come).

(b) An increase in fracking and farming led to an increase in methane emission rates.

(c) The domination of US policy by the GOP (soon including by Donald Trump) and their protection of the fossil fuel industry.

(d) The relatively rapid decline of the coal industry (particularly in China) that has accelerated aerosol forcing.

Thus we should not over rely upon the finding of AR5, as it errs on the side of least drama.

[Daniel B.]

And there are numerous publications showing that the AR5 is erring on the high side.  What is the point?  These are just estimates, with ranges that make them less than useful.  Many assume that the climate sensitivity is a constant, which in all likelihood, is not.  I see several articles making assumption that current conditions are temporary, and that in the future, some forcings will be much worse.  Yet, there is little evidence to support this.  What if the current large changes are what is temporary, and negative feedbacks predominate, leading to moderation?  I notice a lot of ifs, possibilities, and excuses in those references (by the way my reference from 2016 was after AR5).  You seem to be focusing on the worst possible scenarios, rather than the most likely.  The simple fact is that there is a lot that is unknown or uncertain.  Making assumptions and extrapolating from them beyond reference points is a dangerous endeavor, possibly pure folly.   

[TerryM]

Daniel B.
The Cato Institute may not be your best source for scientific accuracy. They are a political advocacy organization that began by promoting the tobacco industry & has a long record of distorting science.
Terry

[Ned W]

In any event, this line of discussion belongs in the "Human Stupidity (Human Mental Illness)" thread

Wow, that's insulting.

[AbruptSLR]

And there are numerous publications showing that the AR5 is erring on the high side.  What is the point?  These are just estimates, with ranges that make them less than useful.  Many assume that the climate sensitivity is a constant, which in all likelihood, is not.  I see several articles making assumption that current conditions are temporary, and that in the future, some forcings will be much worse.  Yet, there is little evidence to support this.  What if the current large changes are what is temporary, and negative feedbacks predominate, leading to moderation?  I notice a lot of ifs, possibilities, and excuses in those references (by the way my reference from 2016 was after AR5).  You seem to be focusing on the worst possible scenarios, rather than the most likely.  The simple fact is that there is a lot that is unknown or uncertain.  Making assumptions and extrapolating from them beyond reference points is a dangerous endeavor, possibly pure folly.   

Any good assessment of risk in a complex situation (see the following World Economic Forum risk report) considered scenarios for maximum credible cases (note the cases for societal collapse and extreme weather in the attached images).  It is beyond believe that you would suggest that because something is complex (such as assessing the upper end of ECS) that we should not assess such maximum credible cases, as AR5 fails to do:

Title: "The Global Risks Report 2017 12th Edition"

http://www3.weforum.org/docs/GRR17_Report_web.pdf

[AbruptSLR]

In any event, this line of discussion belongs in the "Human Stupidity (Human Mental Illness)" thread

Wow, that's insulting.

The title of that thread indicates that it is a sign of mental illness that humans collectively would rather subject society to an increasing risk of socio-economic collapse this century rather than to face the realities of climate change (together with other factors).  Have you looked at that thread, or do you prefer to comment without the benefit of investigation?

Edit: For those who do not know where to find the subject thread, use the link below:

http://forum.arctic-sea-ice.net/index.php/topic,1548.0.html

[Lennart van der Linde]

SPM AR5 Synthesis Report says about tail risks (pp.13 & 17):
https://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf

“For risk assessment, it is important to evaluate the widest possible range of impacts, including low-probability outcomes with large consequences… The design of climate policy is influenced by how individuals and organizations perceive risks and uncertainties and take them into account. Methods of valuation from economic, social and ethical analysis are available to assist decision-making. These methods can take account of a wide range of possible impacts, including low-probability outcomes with large consequences.”

If you read the full report you'll find that potential fat tails likely justify stronger mitigation policies. And that IPCC has been "erring on the side of least drama" seems more likely and better argued than the other way around, as has been discussed at length in earlier parts of this thread.

[AbruptSLR]

Before too many readers gloss over the implications of my Reply #1805 that nicely summarizes lessons learned from comparing CMIP5 to observational data; I provide the attached image from the linked Real Climate article:

Title: "Sensible Questions on Climate Sensitivity"

http://www.realclimate.org/index.php/archives/2017/08/sensible-questions-on-climate-sensitivity/

Please note that in the attached image that the bar for observational ICS values entitled "Marvel et al 2016; Otto et. al. accounting for efficacy" has a median value for ICS of about 3.25C (and an upper value close to 8C); which is close to the median value on the bar entitled "PH17 (w/Lewis Comments)" for the modeled value of ICS.  However, the median value of the modeled ECS value for the bar entitled "PH 17" is close to 3.7C (with an upper value close above 6C).  This is all evidence that AR5 errs on the side of least drama.

[AbruptSLR]

SPM AR5 Synthesis Report says about tail risks (pp.13 & 17):
https://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf

“For risk assessment, it is important to evaluate the widest possible range of impacts, including low-probability outcomes with large consequences… The design of climate policy is influenced by how individuals and organizations perceive risks and uncertainties and take them into account. Methods of valuation from economic, social and ethical analysis are available to assist decision-making. These methods can take account of a wide range of possible impacts, including low-probability outcomes with large consequences.”

If you read the full report you'll find that potential fat tails likely justify stronger mitigation policies. And that IPCC has been "erring on the side of least drama" seems more likely and better argued than the other way around, as has been discussed at length in earlier parts of this thread.

Lennart,
Thank you for citing how AR5 deals with "fat tailed risk by erring on the side of least drama".  In that regards, I repost the following reference by many AR5 contributors who point out that the Carbon Budget given in AR5 is the least relevant metric for real-world policy because it errs so much on the side of least drama that it uses transient climate response, TCR, instead of ECS [which PH17 (Proistosescu and Huybers, 2017) indicates has a median value of about 3.7C based on CMIP5].  Thus Rogelj et al (2016) recommend much more stringent guidelines than the AR5 carbon budget for staying below 2C.

Joeri Rogelj, Michiel Schaeffer, Pierre Friedlingstein, Nathan P. Gillett, Detlef P. van Vuuren, Keywan Riahi, Myles Allen & Reto Knutti (2016), "Differences between carbon budget estimates unravelled", Nature Climate Change, 6, 245–252, doi:10.1038/nclimate2868

http://www.nature.com/nclimate/journal/v6/n3/full/nclimate2868.html?WT.feed_name=subjects_climate-change-mitigation&foxtrotcallback=true

Abstract: "Several methods exist to estimate the cumulative carbon emissions that would keep global warming to below a given temperature limit. Here we review estimates reported by the IPCC and the recent literature, and discuss the reasons underlying their differences. The most scientifically robust number — the carbon budget for CO2-induced warming only — is also the least relevant for real-world policy. Including all greenhouse gases and using methods based on scenarios that avoid instead of exceed a given temperature limit results in lower carbon budgets. For a >66% chance of limiting warming below the internationally agreed temperature limit of 2 °C relative to pre-industrial levels, the most appropriate carbon budget estimate is 590–1,240 GtCO2 from 2015 onwards. Variations within this range depend on the probability of staying below 2 °C and on end-of-century non-CO2 warming. Current CO2 emissions are about 40 GtCO2 yr−1, and global CO2 emissions thus have to be reduced urgently to keep within a 2 °C-compatible budget."

Best regards,
ASLR


Edit: Rogelj et.al. (2016), indicates that the remaining carbon budget from 2015 may be as low as 590 GtCO2; and as CO₂-e emissions are currently around 50GtCO2, it is easy to see that we could locked in to exceeding the 2C limit (sometime before 2100) if we continue BAU emissions thru 2030, assuming that ECS is close to 3C.  However, Sherwood et. al. (2014), finds that ECS cannot be less than 3C, and is likely currently in the 4C to 4.5C range.  If we were to conservatively assume that the effective ECS is currently 4.0C then we passed the threshold to reach 3C GMSTA (circa 2100) when the CO₂-e was about 500ppm around the year 2010 [the 2016 value of CO₂-e atmospheric concentration (with the GWP100 for methane assumed to be 35) was 521ppm, and is climbing rapidly.

Edit 2: For those who think that the Carbon Budget should be calculated using TCR instead of ECS, I point out that PH17 makes it clear that ever since the industrial revolution began in 1750, 90% of the Anthropogenic related increased heat has been going into the ocean where it has been activating slow response (~ 150 to 200 years to active) feedback mechanisms. 

[AbruptSLR]

The following link leads to Cristian Proistosescu's website on Climate Sensitivity, and the two attached images present some of his efforts to better characterize the range of uncertainty on this matter:

https://scholar.harvard.edu/cproist/sensitivity

Caption for first image: "Illustration of the degree to which constraining the fast response constrains  equilibrium sensitivity:  Response functions for CMIP 5 models, computed based on the linear fit of Caldeira and Myhrvold [2013]. Left: Unconstrainted. Right: Constrained such that all models have equal Transient Climate Response (TCR). The remaining spread is associated with inter-model differences in the slow modes of response

Caption for second image: "Empirical estimate of a time-scale-dependent climate sensitivity from Paleoclimate records [Proistosescu and Huybers, forthcoming]."

[AbruptSLR]

With regards to my last two posts Replies #1836 and 1837, on how AR5 deals with “fat tailed risk” by effing on the side of least drama particularly how it uses 'climate sensitivity' (in their case TCR) to calculate their recommended Carbon Budget, I have the following additional comments about AR5's selection process for 'climate sensitivity' for policy making:

1. They use an unweighted combination of paleo, observational and modeled estimate; which prevents the most scientific information (especially from the most advanced ESM projections) to receive their appropriate consideration.

2. They use all published estimates without weighting, which: allows denialist papers that get past peer review to be included; and which allows out of date information to be included.

3. At the publication of AR5, many scientists called for the IPCC to issue updated reports annually so that new findings could be considered in policy but the IPCC did not accept this recommendation.

4. The paleodata of Arctic and Antarctic Amplification can only be replicated by ESM projections with high climate sensitivity.

5. AR5's lower end value for climate sensitivity was based on observational analysis that later was proven to have not appropriately accounted for efficacy of such 'masking' factors as aerosol distribution.

6. PH17 demonstrated that slow response feedback mechanism must be included in policy decisions and not just TCR (as assumed by AR5).

7. There is clear paleodata that climate sensitivity increases with global temperature, but AR5 does not recognize this.

8. Recent observational research indicates that cloud feedback is more positive than AR5 assumed.

9. Recent observational research indicates that many 'slow response' feedback mechanisms are being activated more quickly than assumed by AR5.

[Daniel B.]

SPM AR5 Synthesis Report says about tail risks (pp.13 & 17):
https://www.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_SPM.pdf

“For risk assessment, it is important to evaluate the widest possible range of impacts, including low-probability outcomes with large consequences… The design of climate policy is influenced by how individuals and organizations perceive risks and uncertainties and take them into account. Methods of valuation from economic, social and ethical analysis are available to assist decision-making. These methods can take account of a wide range of possible impacts, including low-probability outcomes with large consequences.”

If you read the full report you'll find that potential fat tails likely justify stronger mitigation policies. And that IPCC has been "erring on the side of least drama" seems more likely and better argued than the other way around, as has been discussed at length in earlier parts of this thread.

Risk assessment definitely has its place.  All types of organizations, from business to government to the military, and especially the insurance industry, use risk assessments.  It is important to estimate accurately both the impacts and probability of such events.  Over-estimating either results in wasted resources.  Under-estimating can result in dire consequences.  The so-called fat tail is speculative; it exists because it is unknown.  That does not increase its probability of occurrence.  Another post mentions that Marvel et al 2016; Otto et. al. accounting for efficacy has a median value for ICS of about 3.25C, but failed to mention that Marvel et al 2016; Lewis & Curry accounting for efficacy has a median value for ICS closer to 2.25C.  Selectively choosing the highest (or lowest) possible value skews risk analysis away from the most probable scenarios, and does a disservice to those who might benefit most.

[jai mitchell]

This is not a "trap."  Snow and melt happen every year.  This past winter's snow were quite excessive, and the summer melt (which appears to have ended) never picked up.   Consequently, Greenland is expected to post a net mass gain of ~500 Gt.  Yes, the ice sheet has been losing mass for a decade, this one year does not make up for past losses.  It may just be an anomaly.  However, dismissing it as erroneous is the bigger trap.

Greenland is expected to post a surface mass balance gain of ~500GT.

The trap is confusing 'surface mass balance' with total mass balance.  Surface mass balance does not include glacier melt/calving.

[jai mitchell]

[...]

Jai, hope you don't mind but there's a question that's been baffling me.   

In this post from another thread, you wrote:

early mortality projections, mainly in sub-sahara Africa  and SE Asia under a >2.0C warming scenario are in excess of 1 billion human beings.

Geoff Beacon asked for a source, and you replied with this:

http://apps.who.int/iris/bitstream/10665/134014/1/9789241507691_eng.pdf

    Climate change is projected to have substantial adverse impacts on future mortality, even
    under optimistic scenarios of future socioeconomic development. Under a base case
    socioeconomic scenario, we estimate approximately 250 000 additional deaths due to climate
    change per year between 2030 and 2050.

https://forum.arctic-sea-ice.net/index.php/topic,1920.msg108521.html#msg108521

Perhaps I'm missing something obvious, but I don't understand how you went from "250,000 additional deaths ... per year between 2030 and 2050" to "mortality projections ... are in excess of 1 billion human beings"  250,000 cases/year x 20 years is 5 million, not over 1 billion.

Was there some additional aspect that I'm missing?  Just curious.

The report looked only at A1B emission scenario temp response between 2030-2050  this temperature range is from about +.85 to +1.5C (from 2000) (see graph below). We are already at the +.65C (from 2000) value today.  The temp regime will reach the +1.5C by 2035.

They also state in the report that they are not including other impacts like migration and conflict.  If you look at the gridded surface temperature response to warming, at +2.0C, sub-sahara africa will experience +3.5C  and at +4.0C it will be +6.0C.

If you project the human mortality based on current conflicts (in Yemen for example) and severe droughts (in Ethiopia) and include time periods through 2100 and even beyond.  The mortality rate goes up far beyond the analysis in the report. 

The 2 billion human deaths projection is my own.

[AbruptSLR]

The so-called fat tail is speculative; it exists because it is unknown.  That does not increase its probability of occurrence.  Another post mentions that Marvel et al 2016; Otto et. al. accounting for efficacy has a median value for ICS of about 3.25C, but failed to mention that Marvel et al 2016; Lewis & Curry accounting for efficacy has a median value for ICS closer to 2.25C.  Selectively choosing the highest (or lowest) possible value skews risk analysis away from the most probable scenarios, and does a disservice to those who might benefit most.

First, the entire area under a probability density function, PDF, is uncertain which is why it is a PDF, and the fat tail of a PDF should be dealt with like the rest of the curve, but denialists general support the practice of ignoring the fat tail for policy making, which is not scientific.

Second, the area under the fat tail can increase with time not only because more research can identify valid feedback mechanisms that were ignored when the priori PDF was made; but also because society has stayed on a BAU pathway since the AR5 PDFs were made.

Third, in a real-world risk assessment equal weight does not need to be given to quasi-denialists like Lewis and Curry, unfortunately the IPCC does give their peer reviewed research equal weight.

Lastly, I note that this discussion cannot only be about the trend line value of ECS, and the historical record is full of multi-decadal spikes in warming associated with such temporary natural radiative forcing input at:
- Rapid permafrost degradation (see the attach NYT image of permafrost currently degrading in Alaska) especially including methane from thermokaust lakes;
- Hansen's ice-climate feedback, should the WAIS collapse this century;
- Collapse of tropical rainforests this century and the carbon emissions from their decaying vegetation;
- A possible ENSO climate attractor amplification this century;
- Wildfires and wars.

Links to NYT images of Alaska permafrost:

https://www.nytimes.com/interactive/2017/08/23/climate/alaska-permafrost-thawing.html?rref=collection%2Fsectioncollection%2Fclimate&action=click&contentCollection=climate&region=rank&module=package&version=highlights&contentPlacement=1&pgtype=sectionfront&_r=0
&
https://www.nytimes.com/section/climate?action=click&contentCollection=Climate&region=TopBar&module=HomePage-Title&pgtype=Multimedia

[Daniel B.]

Third, in a real-world risk assessment equal weight does not need to be given to quasi-denialists like Lewis and Curry, unfortunately the IPCC does give their peer reviewed research equal weight.

Actually, the IPCC should give equal weight to all the climate peer reviewed research.  To selectively choose those works that align with a particular ideology is quite unscientific.

[jai mitchell]

Third, in a real-world risk assessment equal weight does not need to be given to quasi-denialists like Lewis and Curry, unfortunately the IPCC does give their peer reviewed research equal weight.

Actually, the IPCC should give equal weight to all the climate peer reviewed research.  To selectively choose those works that align with a particular ideology is quite unscientific.

I agree, the current work is a balance of the entire body of published work, therefore the outliers, ones that go against hundreds of papers and historic trends, even though they are peer reviewed, are not included in the final average projections.  Of course, the real problem here is the fact that new science work is overwhelmingly showing that previous IPCC projections were severely conservative in their estimations.

This has been shown through the iteration of projections from FAR and SAR and through the AR5.  Most specifically, in their neglecting to include emissions from melting permafrost, COMPLETELY, from their temperature projections in the Fifth Assessment in 2013.

[AbruptSLR]

Actually, the IPCC should give equal weight to all the climate peer reviewed research.  To selectively choose those works that align with a particular ideology is quite unscientific.

While you are correct that AR6 will apply equal weight to all peer reviewed papers; there are many peer reviewed scientific papers that have subsequently been proven to be incorrect (many denialist papers have subsequently been proven incorrect) and if so it is unscientific to still give them equal weight.

[gerontocrat]

What will AR6 say in the next IPCC report ? Do not answer, today has been a rotten day already.

[rboyd]

The whole discussion reminds me of the financial risk modelling in the bank that I was working in in the 2000's. Assumed a normal distribution from historical data for "Value at Risk" (a decade or so was all that was available for many instruments!) and smoothly functioning markets where liquidity (an eager buyer) was always available. Plus a few "stress tests" which were not very stressful.

Their version of "paleo" was the 1929 crash and then the financial panics of the 1800's. These show that under stress financial markets are highly stochastic, have big fat tails, and liquidity can completely vanish (no buyers = massive 'air pocket' drops in prices). These were not deemed to be that relevant, given the very different financial markets of the time. "Modern" financial markets would never have such problems!

The other issue was that if the models accurately reflected the risk in the market, the bank would have to take less risk (less profit to drive up bonuses) and/or hold back more safe capital (reducing the rate of return). Such considerations wouldn't affect the conservativeness of the modellers, who worked for the guys benefitting from the big bonuses (the modellers got pretty big bonuses as well)?!

Along came 2008 and everyone sang the same song "we never saw it coming", took their free bailout money, kept the bonuses, and went on as before. Waiting for the "oh my god!" moment from the politicians, it may take a while ... After all, most of them are bought and paid for by the businesses benefitting from continued fossil-fuelled growth.

Most climate modellers are not that well paid, but there is an army of powerful opponents ready to jump on anyone who gets out of line and starts telling the truth. So, I cant really blame them. They have mortgages, children etc. to pay for. Then of course, there is the innate conservativeness of scientists. Trump of course, just makes this much worse. As does the neo-liberalization of academia over the past few decades.

The focus on CO2 only, excluding the other GHG's, drives me crazy. Even if we accept the bullshit excuse that the F-gases and CH4 have low atmospheric residence times (but what about the next 20 years? but the concentration levels of CH4 are not falling, they are rising?) the quoted numbers should at least inculde N20 if we are talking about this century.

[Daniel B.]

The whole discussion reminds me of the financial risk modelling in the bank that I was working in in the 2000's. Assumed a normal distribution from historical data for "Value at Risk" (a decade or so was all that was available for many instruments!) and smoothly functioning markets where liquidity (an eager buyer) was always available. Plus a few "stress tests" which were not very stressful.

Their version of "paleo" was the 1929 crash and then the financial panics of the 1800's. These show that under stress financial markets are highly stochastic, have big fat tails, and liquidity can completely vanish (no buyers = massive 'air pocket' drops in prices). These were not deemed to be that relevant, given the very different financial markets of the time. "Modern" financial markets would never have such problems!

The other issue was that if the models accurately reflected the risk in the market, the bank would have to take less risk (less profit to drive up bonuses) and/or hold back more safe capital (reducing the rate of return). Such considerations wouldn't affect the conservativeness of the modellers, who worked for the guys benefitting from the big bonuses (the modellers got pretty big bonuses as well)?!

Along came 2008 and everyone sang the same song "we never saw it coming", took their free bailout money, kept the bonuses, and went on as before. Waiting for the "oh my god!" moment from the politicians, it may take a while ... After all, most of them are bought and paid for by the businesses benefitting from continued fossil-fuelled growth.

Most climate modellers are not that well paid, but there is an army of powerful opponents ready to jump on anyone who gets out of line and starts telling the truth. So, I cant really blame them. They have mortgages, children etc. to pay for. Then of course, there is the innate conservativeness of scientists. Trump of course, just makes this much worse. As does the neo-liberalization of academia over the past few decades.

The focus on CO2 only, excluding the other GHG's, drives me crazy. Even if we accept the bullshit excuse that the F-gases and CH4 have low atmospheric residence times (but what about the next 20 years? but the concentration levels of CH4 are not falling, they are rising?) the quoted numbers should at least inculde N20 if we are talking about this century.

Yes.  The problem of criticizing anyone who steps out of line [with one's own views], and starts telling the truth [or a different version of the truth] must stop.  Not everything will conform to the majority.  Marshall and Warren were awarded the nobel prize in medicine for their work, which went against the majority.  Sometimes, contrarian opinions are just rubbish.  Other times, they help further scientific understand.  To dismiss them outright [as some here would have], reeks of bias and prejudice, and diminishes the role of science.

[AbruptSLR]

The following linked Skeptical Science article (and associated extract) states that when Kummer & Dessler (2014) (see reference at bottom of this post) calculate that the best estimate of ECS is 3oC, they conservatively assume that climate is 33% more sensitive to changes in aerosols and ozone than greenhouse gases; however, Shindell (2014) showed that climate is more sensitive to changes in aerosols and ozone than greenhouse gases perhaps by as much as 50%.  Therefore, perhaps Kummer & Dessler are under estimating the best value of ECS by as much as 50%/33%, or by a factor of about 1.5.  If so then based on Shindell (2014) the best estimate of ECS may perhaps be 4.5 ^oC instead of 3 ^oC.

https://www.skepticalscience.com/sense-and-climate-sensitivity-kummer-dessler-2014.html

Extract: "In short, Shindell showed that according to models, the climate is significantly more sensitive to changes in aerosols and ozone than greenhouse gases, perhaps by as much as 50%. Kummer & Dessler showed that if the climate is 33% more sensitive to changes in aerosols and ozone, then the 'instrumental' estimates are right in line with those derived from historical climate changes and global climate models, with a best estimate of 3°C warming in response to a doubling of atmospheric CO2."

J.R. Kummer and A.E. Dessler, (2014), "The impact of forcing efficacy on the equilibrium climate sensitivity", Geophysical Research Letters, DOI: 10.1002/2014GL06004

http://onlinelibrary.wiley.com/doi/10.1002/2014GL060046/abstract