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Messages - Lennart van der Linde

Pages: [1]
1
Hefaistos,
Can you clarify what you mean?

Indeed, if you share 350 ppm as a desirable goal, then this implies net zero globally by 2050 to minimize the risk that tipping points will be crossed that will make 350 impossible to reach, as far as I understand.

2
Hansen's model(s), that he has published in several papers since 2005, is in my opinion not accepted science... He speculates that exponentially increasing ice losses primarily from the Antarctic will cause the AMOC/SMOC to shut down within a few decades, which will trigger more large-scale climate changes. But this is just a modelling excercise, based on incomplete theories, and totally insufficient data, especially from the ever important Southern Ocean... And we aren't yet able to adequately model deep convection in the tropics, where most of energy transfer takes place. Etc.etc., just to point out that we shouldn't get panic because of some computer simulations that is essentially GIGO.
...
I agree about the urgency of climate policies to avoid the 'tipping points'. But I think that:
i. The capitalist market forces already strongly favouring renewables due to pure price competitiveness; and
ii. The kind of aggressive climate policies now implemented by the EU and some other OECD countries; will be quite sufficient to avoid those tipping points in reasonable time, say 40 years. I think we already left the exponential growth of CO2, and that we are now in linear growth. In as little as 5-10 years I hypothesize that we will see flat CO2 growth.

I hope you're right, but would not count on it. Hansen has a history of becoming accepted science after first being contested (by some). He may be wrong this time, but it seems very possible that he's right again. And many of his suspicions are being shared by prominent and respected scientists in their fields. Waiting with stronger mitigation until we have more certainty about the accuracy of their suspicions implies risking being too late (even more than we already are), precisely because of the inertia in the climate system, which Hansen emphasizes. Gambling with such stakes involved seems very irresponsible. To minimize the unacceptably large risk of passing dangerous tipping points we have to reach net zero globally within 30 years, not 40 years, or as fast as possible, as Hansen says. This means the EU and other richer parts of the world have to reach net zero in about 20 years, or pay poorer countries to reduce their emissions even faster than otherwise. Where the market can do this, great. But where the market cannot do this fast enough yet, stronger policies will have to accelerate their development. The EU is making some progress in the right direction, at least on paper, but more will be needed and has to be implemented. My two cents.

3
(why 350? I should be 280 I think. To pick up where we left of, although I don't think that is possible within the next 10000 years)

Jim Hansen says in his latest communication:
http://www.columbia.edu/~jeh1/mailings/2019/20191211_Fire.pdf

'I may have learned more in 2004-2008 than I had in the prior 15 years – about climate science as well as implications for energy policy. Bill McKibben, who was about to form an organization 450.org, asked me to confirm that 450 parts per million (ppm) was an appropriate target for atmospheric CO2 amount. This led to collaboration with some of the best relevant scientists in the world. We concluded that the appropriate target was less than 350 ppm. The optimum target is probably not as low as the preindustrial 280 ppm, in part because of other human-made alterations to Earth, but it is unnecessary to define the final target exactly at this time. The “<350 ppm” target already implies that fossil fuel emissions must be phased out as rapidly as practical.'

4
'We' tend to focus a bit too much on what's going on in the atmosphere and 'forget' about the more important role that the Ocean plays in long-term climate change.

Hefaistos, I think many on this forum/thread have learned a lot from scientists like Jim Hansen. Have you seen his latest commentary? See:
http://www.columbia.edu/~jeh1/mailings/2019/20191211_Fire.pdf

Do you think he 'forgets' about the more important role of the ocean? Or does he indicate mainstream climate science has maybe even under-estimated the role of the ocean, both in the longer and also the shorter term?

Also see what he says there about the role of the market versus instruments like fee & dividend. Do you agree with him about the urgency of such policies? Or do you believe the market will solve this crisis in time all by itself? And two generations may well be too long to prevent a cascade of tipping points, so how can 'we' minimize this risk?

5
Also see Turner er al 2017, who think the methane sink may have shrunk:
https://www.pnas.org/content/114/21/5367

6
Certainly fracking of natural gas is one source of atmospheric methane; however, the northern wetlands (including the tundra) is another significant source and the attached atmospheric methane concentration graph from Barrow, Alaska (from 2005 to Dec 9, 2019) shows a recent surge in local methane concentrations suggesting a local methane emission source (such as northern wetlands).

At AGU Saunois et al (submitted) think growing methane emissions come entirely from South East Asia and Africa. See these tweets from Zeke Hausfather:
https://twitter.com/hausfath/status/1204549028333023232

And the submitted paper by Saunois et al:
https://www.earth-syst-sci-data-discuss.net/essd-2019-128/

7
So a natural super-interglacial has been turned by us into a super-super-interglacial, and maybe we're even tipping the planet into a Hothouse Earth state:
https://www.pnas.org/content/115/33/8252

Again, I should have formulated more precisely, as Steffen et al 2018 do in their Hothouse Earth paper, referring to Ganopolski et al 2016:
"the rapid trajectory of the climate system over the past half-century along with technological lock in and socioeconomic inertia in human systems commit the climate system to conditions beyond the envelope of past interglacial conditions. We, therefore, suggest that the Earth System may already have passed one “fork in the road” of potential pathways, a bifurcation (near A in Fig. 1) taking the Earth System out of the next glaciation cycle (11)."

Maybe we've already passed this fork in the road, or maybe not. In risky territory we certainly seem to be.

8
Quote from: Lennart van der Linde link=topic=2205.msg239688#msg239688
Several recent interglacials had even a little less ice than the current interglacial (which by human interference has stopped being an interglacial, or turned into a super-interglacial of at least 50,000-100,000 years).

I myself didn't remember Ganopolski et al 2016 carefully enough:
https://www.nature.com/articles/nature18452

They say:
"our analysis suggests that even in the absence of human perturbations no substantial build-up of ice sheets would occur within the next several thousand years and that the current interglacial would probably last for another 50,000 years. However, moderate anthropogenic cumulative CO2 emissions of 1,000 to 1,500 gigatonnes of carbon will postpone the next glacial inception by at least 100,000 years. Our simulations demonstrate that under natural conditions alone the Earth system would be expected to remain in the present delicately balanced interglacial climate state, steering clear of both large-scale glaciation of the Northern Hemisphere and its complete deglaciation, for an unusually long time."

So a natural super-interglacial has been turned by us into a super-super-interglacial, and maybe we're even tipping the planet into a Hothouse Earth state:
https://www.pnas.org/content/115/33/8252

9
During the glacial periods of the ice ages, ice sheets were far more extensive than they are today.

Yes, certainly, but during the Pliocene there was much less ice than now, and than during other recent interglacials.

Kohler et al 2015 say, as quoted by ASLR and yourself earlier:
"During Pleistocene intermediate glaciated climates and interglacial periods, S[CO2,LI] is on average ~45 % larger than during Pleistocene full glacial conditions."

Several recent interglacials had even a little less ice than the current interglacial (which by human interference has stopped being an interglacial, or turned into a super-interglacial of at least 50,000-100,000 years).

It looks to me you're not reading Kohler et al carefully enough.

10
They are comparing a time without the large North American and Eurasian ice sheets (kinda like
now) to the time when those ice sheets were melting (like 25,000 to 10,000 years ago).

Don't they include the Greenland Ice Sheet among the large Northern ice sheets? This ice sheet was largely present during the interglacials of the (late) Pleistocene, and not during the Pliocene.

Kohler et al 2015 say:
"Whether climate in the future is more comparable to the climate states of interglacials of the late Pleistocene or to the warm Pliocene is difficult to say, although this has, according to our results, major implications for the expected equilibrium temperature rise... The data available so far suggest that the appearance of northern hemispheric land ice sheets changed the climate system and accordingly influenced climate sensitivity. In the Pliocene, STCO2,LIU was therefore probably smaller than during the interglacials of the Pleistocene."

So, it seems to me that ASLR is right in pointing to the probability that ECS is larger now than during full glacial conditions or during Pliocene conditions.

11
a lot of posters on this forum seem to think that we're doomed and it's too late to do anything.

My impression is that a lot of posters are concerned we're not doing as much as we can, and should, because powerful forces do not think it necessary and/or desirable to do more than we're doing (which has not been much so far).

12
Models not running hot, but pretty accurate, according to Hausfather et al 2019:
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL085378

"Plain Language Summary
Climate models provide an important way to understand future changes in the Earth's climate. In this paper we undertake a thorough evaluation of the performance of various climate models published between the early 1970s and the late 2000s. Specifically, we look at how well models project global warming in the years after they were published by comparing them to observed temperature changes. Model projections rely on two things to accurately match observations: accurate modeling of climate physics, and accurate assumptions around future emissions of CO2 and other factors affecting the climate. The best physics‐based model will still be inaccurate if it is driven by future changes in emissions that differ from reality. To account for this, we look at how the relationship between temperature and atmospheric CO2 (and other climate drivers) differs between models and observations. We find that climate models published over the past five decades were generally quite accurate in predicting global warming in the years after publication, particularly when accounting for differences between modeled and actual changes in atmospheric CO2 and other climate drivers. This research should help resolve public confusion around the performance of past climate modeling efforts, and increases our confidence that models are accurately projecting global warming."

13
Science / Re: 2019 Mauna Loa CO2 levels
« on: December 01, 2019, 12:33:24 PM »
Again, lot's of forecasts and dire warnings.
Climate reanalyzer shows no big trend for precipitation the last 40 years. About one percent up. And declining slightly during the last 10 years.
Agreed, this is the aggregate.

More intense droughts and more intense precipitation will probably show no big trends in aggregate precipitation. And forecasts/projections matter, especially in inert systems. As Diffenbaugh & Field 2013 show the current and coming antropogenic warming may well be 10-100 times faster than any warming in the past 65 million years:
https://denning.atmos.colostate.edu/readings/Impacts/Ecosystems.Science-2013-Diffenbaugh-486-92.pdf

How hard will it be for life, including human civilization, to adapt to such an unprecedented rapid climate shift? Should we take the risk to find out? On paper thru the Paris Agreement humanity decided we should not take that risk. Our practical behaviour and policies do not conform to this agreement yet. This is troubling in light of the risk of crossing potential tipping points even below two degrees C. Your persistent downplaying of this risk seems quite irrational and irresponsible. Why are you apparently so unwilling to take the science pointing to this risk seriously?

14
Science / Re: 2019 Mauna Loa CO2 levels
« on: November 30, 2019, 10:13:02 AM »
Greenhouse gas emissions have risen 1.5 percent each year on average over the past decade, despite a slight levelling off during 2014-16.

“There is no sign of a slowdown, let alone a decline, in greenhouse gases concentration in the atmosphere despite all the commitments under the Paris agreement,” said Petteri Taalas, secretary-general of the World Meteorological Organization.

“It is worth recalling that the last time the Earth experienced a comparable concentration of CO2 was 3 to 5 million years ago,” he added. “Back then, the temperature was 2 to 3°C warmer, and sea level was 10 to 20 meters higher than now.”

And GHG concentrations have risen quite exponentially by about 1.66% per year on average over the past four decades, while they have reached about 500 ppm CO2-eq by now, as shown here and below: https://www.esrl.noaa.gov/gmd/aggi/aggi.html

When was the last time GHG concentrations were this high? Maybe 20 million years ago?

15
Science / Re: 2019 Mauna Loa CO2 levels
« on: November 29, 2019, 07:51:26 PM »
Capitalism now brings major action and change all by itself. Relative prices of coal and renewables for power generation have changed so that it's not economical to build for coal anymore. Coal usage already in decline.
Yes, CO2 will continue to increase, but even if we just change from exponential growth to linear growth, as indicated by Wolfpack's polynomial, it is great news.

If... That's a big if. So far the growth rate of CO2 concentration is still growing, as shown here and below: https://www.esrl.noaa.gov/gmd/ccgg/trends/gr.html

One decade of a little slower growth doesn't mean an end of the acceleration, as shown. Whether the use of fossil fuels will decline and keep declining, remains to be seen. We have to do what we can to hasten their decline, as positive feedbacks can cause further increases in GHG-concentrations thru less uptake by and more release from natural carbon sinks. We can and should try desperately to remain optimistic, but without losing sight of reality. We have a lot of work to do before we can be confidently optimistic.

16
Yes, we need to get off of fossil fuels as soon as possible.  However [...] we're making great progress in doing so [...] Even with the additional carbon being released in the Arctic due to warming, the reduction in CO2 and methane from eliminating those two sources of anthropogenic emissions will result in emissions closer to the RCP 2.6 scenario than the RCP 8.5 scenario.

Lenton et al 2019 say:
"If current national pledges to reduce greenhouse-gas emissions are implemented — and that’s a big ‘if’ — they are likely to result in at least 3 °C of global warming. This is despite the goal of the 2015 Paris agreement to limit warming to well below 2 °C. Some economists, assuming that climate tipping points are of very low probability (even if they would be catastrophic), have suggested that 3 °C warming is optimal from a cost–benefit perspective. However, if tipping points are looking more likely, then the ‘optimal policy’ recommendation of simple cost–benefit climate-economy models aligns with those of the recent IPCC report. In other words, warming must be limited to 1.5 °C. This requires an emergency response [...] Early results from the latest climate models — run for the IPCC’s sixth assessment report, due in 2021 — indicate a much larger climate sensitivity (defined as the temperature response to doubling of atmospheric CO2) than in previous models. Many more results are pending and further investigation is required, but to us, these preliminary results hint that a global tipping point is possible [...] Some scientists counter that the possibility of global tipping remains highly speculative. It is our position that, given its huge impact and irreversible nature, any serious risk assessment must consider the evidence, however limited our understanding might still be. To err on the side of danger is not a responsible option. If damaging tipping cascades can occur and a global tipping point cannot be ruled out, then this is an existential threat to civilization. No amount of economic cost–benefit analysis is going to help us. We need to change our approach to the climate problem. In our view, the evidence from tipping points alone suggests that we are in a state of planetary emergency: both the risk and urgency of the situation are acute."

Let's take the science seriously and recognize the urgency that Lenton et al, ASLR and others describe and justly emphasize as a planetary emergency and existential threat. Downplaying this inconvenient truth may be a natural impulse, but has been done for too long and is nog helping us. Let's face reality and the risks it entails and do what we have to do to minimize those risks, while we still can.

17
Hawkins lists various reasons why there is a discrepancy. Nr 3: "the real world may have a climate sensitivity towards the lower end of the CMIP5 range."
I guess he nailed it there.
If that was true for CMIP5, the CMIP6 models with much higher ECS around or above 5 will have an even tougher fight with reality.

Lewandowsky et al 2018  analyze data up until 2016. If you go back to the figure I attached in Reply #2016 the discrepancy looked less worrying with those data ending in 2016. But when we include 2017 and 2018 in the dataset and compare with the models, we get the impression that actual temperatures follow a lower trajectory, a lower trend, than the models. They write:
"...several biases in the observations and in model projections gave rise to the impression of a divergence between modeled and observed temperature trends. This impression was limited to the period 2011–2013, after which the ongoing debiasing eliminated any appearance of a divergence. During the period 2011–2013, the impression of a divergence could appear to be statistically significant, but only if the selection-bias issue was ignored. "

They might have been correct about selection bias, if it wasn't for a repeat of same in 2017-18. With two more years of data, the divergence seems to become only stronger.

It seems to me you're jumping to conclusions from hypotheses that have not been confirmed or not properly investigated yet. Hawkins lists several hypothetical explanations for the discrepancy between observations and simulations without saying which explanation he thinks is responsible for which part of the discrepancy, if at all. So your guess is as good as any, but needs to be properly investigated first. Lewandowsky et al give some first results from their investigation and do not confirm your guess. Maybe this is because they have not taken the latest years into account yet, but that remains to be seen. If two more years of data would indeed show a significant divergence, then two or more years of data after 2018 may change the picture once again. So it seems a little early to jump to the conclusion that the models are running hot, the more so as ASLR has shown several studies that indicate the ECS may be or may become higher with further warming. Proper risk management would take this possibility into account and demands a little more critical reasoning than you've been showing here so far, if you ask me.

18
Nothing peer reviewed, but prof. Ed Hawkins makes regular updates to evaluate model performance. Models evidently running hot.

http://www.met.reading.ac.uk/~ed/home/index.php
https://www.climate-lab-book.ac.uk/comparing-cmip5-observations/

It may be evident to you, but apparently not to Hawkins himself, and not to peer-reviewed Lewandowsky et al 2018 either.

Hawkins writes on his blog:
"The simulation data uses spatially complete coverage of surface air temperature whereas the observations use a spatially incomplete mix of air temperatures over land and sea surface temperatures over the ocean. It is expected that this factor alone would cause the observations to show smaller trends than the simulations."

He gives some other potential explanations for the apparent divergence as well:
"There are several possible explanations for why the earlier observations are at the lower end of the CMIP5 range. First, there is internal climate variability, which can cause temperatures to temporarily rise faster or slower than expected. Second, the radiative forcings used after 2005 are from the RCPs, rather than as observed. Given that there have been some small volcanic eruptions and a dip in solar activity, this has likely caused some of the apparent discrepancy. Third, the real world may have a climate sensitivity towards the lower end of the CMIP5 range. Next, the exact position of the observations within the CMIP5 range depends slightly on the reference period chosen. Lastly, this is not an apples-with-apples comparison because it is comparing air temperatures everywhere (simulations) with blended and sparse observations of air temperature and sea temperatures. A combination of some of these factors is likely responsible."

Lewandowsky et al 2018  elaborate on this:
https://iopscience.iop.org/article/10.1088/1748-9326/aaf372/meta

"The impression of a divergence early in the 21st century was caused by various biases in model interpretation and in the observations, and was unsupported by robust statistics [...] IPCC Assessment Report (AR5)... stated that '...111 out of 114 realizations show a GMST trend over 1998–2012 that is higher than the entire HadCRUT4 trend ensemble... This difference between simulated and observed trends could be caused by some combination of (a) internal climate variability, (b) missing or incorrect radiative forcing and (c) model response error' (Flato et al 2013, p 769). The consensus view expressed by the IPCC therefore pointed to a divergence between modeled and observed temperature trends, putatively caused by a mix of three factors. Subsequent to the IPCC report, the role of these three factors has become clearer [...] We have established that several biases in the observations and in model projections gave rise to the impression of a divergence between modeled and observed temperature trends. This impression was limited to the period 2011–2013, after which the ongoing debiasing eliminated any appearance of a divergence. During the period 2011–2013, the impression of a divergence could appear to be statistically significant, but only if the selection-bias issue was ignored. We have shown that ignoring of the selection-bias issue can drastically inflate Type-I error rates, which renders the inferences unreliable and in this case erroneous."

See their full paper for further details.
What do you think of their conclusions?

19
See for example Lewandowsky et al 2018:
https://iopscience.iop.org/article/10.1088/1748-9326/aaf372/pdf

Abstract
We review the evidence for a putative early 21st-century divergence between global mean surface temperature (GMST) and Coupled Model Intercomparison Project Phase 5 (CMIP5) projections. We provide a systematic comparison between temperatures and projections using historical versions of GMSTproducts and historical versions of model projections that existed at the times when claims about a divergence were made. The comparisons are conducted with a variety of statistical techniques that correct for problems in previous work, including using continuous trends and a Monte Carlo approach to simulate internal variability. The results show that there is no robust statistical evidence for a divergence between models and observations. The impression of a divergence early in the 21st century was caused by various biases in model interpretation and in the observations, and was unsupported by robust statistics.

20
The issue here is that these models are demonstrably unreliable in terms of forecasting global warming - they're running hot.

Can you point us to some peer-reviewed science that demonstrates the models are running hot, and to what extent?
As far as I know they're pretty much on target, but maybe I've missed the relevant science.

21
The basic concept of LTG is that there are limited resources, and that mankind is depleting those resources in such a way that it triggers more or less uncontrollable dynamic developments regarding environment etc.
This concept is faulty. Resources will get higher relative prices the scarcer they become. But they won't be physically depleted. That was the first big modelling mistake they made.
The second big mistake was to disregard all technical development. This is also connected with the changing relative prices: when an essential resource gets a higher price due to scarcity, it will trigger developments to either replace that resource with substitutes or find ways to improve the extraction or production of the resource [...]
The third modelling mistake was to not include counteractions by TPTB.
That said, I agree with what you say about ecological boundaries. Capitalism needs regulation.

Below a few quotes from Limits to Growth 1972 and the 30-year update Limits to Growth 2004 that seem to contradict your assertions. Paraphrased Meadows et al say:
- dynamics only become uncontrollable if we wait too long to consciously limit material growth
- even when higher prices for scarcer resources lead to technological innovation and substitution in the short run the total supply of resources remains limited in the longer run
- counteractions by TPTB have been modelled in the several scenario's, including a scenario that avoids collapse by consciously limiting further material growth

Meadows et al argue that the longer we postpone implementing policies to limit material growth, the higher the risk of eventual collapse, without being able to predict exactly when this collapse may occur. In (most of) their scenario's this collapse would occur somewhere during this century, mainly depending on the exact ecological and technological limits.

The current climate crisis seems the ultimate illustration of the general accuracy of their analysis, with climate scientists showing we need extremely rapid emission reductions to avoid passing potentially catastrophic climate tipping points, while energy experts argue that such rapid reductions hardly seem possible without (in the short run) shrinking the global economy, or at least the material consumption in the richer economies.

So the crucial question seems to be: how long do we want to keep gambling with the future of our children? Or alternatively: how certain can we be that we're not risking their future by holding on to business-as-usual policies aimed at continued material growth?

22
If you reject the fundamental influence of market forces you always risk repeating the mistake of the Club of Rome report "Limits to growth".

Have you actually read "Limits to Growth"? If so, where exactly did you find the mistake?
As far as I know they didn't reject the fundamental influence of market forces at all, but maybe I missed it.
Even market forces cannot provide unlimited material growth on a finite planet.
Current market forces are already exceeding several planetary ecological boundaries.
The longer this overshoot lasts, the higher the risk of eventual collapse.
Only by governing market forces can we hope to still avoid this collapse, or at least make its impact less destructive.
This is how I understand the Club of Rome's warning of 1972 (updated several times since), which still seems very accurate to me.

23
[Are lower latitudes warming? No, see attached, we have a negative SST trend in Antarctic seas.

Antarctic seas are at higher latitudes, not lower. Lower latitudes are closer to the equator.

24
Hansen et al 2016:
https://pubs.giss.nasa.gov/abs/ha04710s.html

"Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10-40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500-2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing [...] The modeling, paleoclimate evidence, and ongoing observations together imply that 2°C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50-150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments."

Silvano et al 2018:
https://advances.sciencemag.org/content/4/4/eaap9467

"Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise."

25
Here are the projections for RCP 8.5 from DeConto and Pollard 2016:

https://www.geo.umass.edu/climate/papers2/DeConto2016.pdf

Quote
Antarctica contributes 77 cm of GMSL rise by 2100, and continued loss of the Ross and Weddell Sea ice shelves drives WAIS retreat from three sides simultaneously (the Amundsen, Ross, and Weddell seas), all with reverse-sloping beds into the deep ice-sheet interior. As a result, WAIS collapses within 250 years. At the same time, steady retreat into the Wilkes and Aurora basins... adds substantially to the rate of sea-level rise, exceeding 4 cm yr−1 (Fig. 4c) in the next century, which is comparable to maximum rates of sea-level rise during the last deglaciation.

So in the worst case emissions scenario, which is no longer feasible because we aren't going to burn that much coal, the West Antarctic ice shelves collapse after the Larsen C, which collapses in the 2050s. The Wilkes and Aurora basins would contribute to sea level rise next century, after 2100.

And Rob DeConto has publicly backed off of these projections.

https://www.theatlantic.com/science/archive/2019/01/sea-level-rise-may-not-become-catastrophic-until-after-2100/579478/

Quote
In new work, conducted with three other prominent glaciologists, DeConto and Pollard have lowered some of their worst-case projections for the 21st century. Antarctica may only contribute about a foot of sea-level rise by 2100, they now say. This finding, reached after the team improved their own ice model, is much closer to projections made by other glaciologists... Now their worst-case skyrocketing sea-level scenario seems extremely unlikely, at least within our own lifetimes.

Skeptical Science has a very good overview of MICI.

https://skepticalscience.com/new-light-antarctica-contribution-slr.html

Quote
DeConto says he is not able to comment on it directly as it is undergoing peer review. However, he has presented some preliminary results at the Fall Meeting of the American Geophysical Union (AGU) in December.

So to recap:
- AbruptSLR continues to confuse the timeframes of the original MICI models published in 2016
- The authors of the original MICI models now state that the 2016 projections were too pessimistic
- Other studies have shown that ice flows instead of fails in a brittle manner, which casts doubt on the mechanism needed for MICI to occur.
- Past sea level rise could have occurred without needing the MICI mechanism
- MICI needs hydrofracturing to occur before MICI can occur and yet there are areas in Antarctica where water flows off the ice sheet rather than penetrating through it to create hydrofractures
- Coal is now more expensive than solar and wind power and coal use is expected to peak next decade, so the emission projections of RCP 8.5 from the 2020s through 2100 aren't possible.

Ken,
Wilkes and Aurora reach their maximum rate of ice loss in the next century, but apparently start to contribute significantly already this century, in my understanding of your quotes of DeConto & Pollard.

And while their new results for 2100 seem to be lower than their earlier results, they also warned that after 2100 the rate of ice loss could be even higher than they found earlier, if I remember correctly. Richard Alley also warns for this possibility in this recent news item:
https://insideclimatenews.org/news/12112019/antarctica-ice-shelf-melt-atmospheric-river-thwaites-glacier-ocean-sea-level-rise?utm_source=facebook&utm_medium=social&fbclid=IwAR0gFMMYkF2K6-PP99Dwonon5CJ-E5TsEmSK5oJSuC4B0Bh-0w9HJjC3Nkw

Quote
Alley noted that some research has suggested that, if global warming pushes West Antarctica's towering ice cliffs to collapse, it could raise sea level more than 3 feet by 2100, surging to 50 feet by 2500, from Antarctic ice melt alone.

"That model is sometimes treated as a worst-case scenario, but in fact the model used a maximum calving rate that has briefly been exceeded in Greenland already, and the possibility exists that even faster calving could occur from higher, wider cliffs that could develop in Antarctica," he said.

Even the most recent international assessment of ice loss relies on models that don't account for some of those ice shelf tipping points, he said. "If we're fortunate, and the ice shelves are retained, then these models may be accurate. If we do lose the ice shelves, the models may project less sea level rise than will occur, perhaps by a lot."

Everyone hopes we'll be lucky, but we can't count on that, so the strongest possible mitigation is urgent and preparing for strong adaptation is urgent as well. RCP8.5 may not be likely, but with people like Trump in power we can't be sure either that it will not come to pass. And also with lower RCP's the risks of rapid and large SLR remain substantial, so it seems reasonable to be very aware of those risks and to not underplay them, as has been done for decades now. It seems to me your posts have a tendency to "err on the side of least drama", like many IPCC reports so far, as argued by Brysse et al and others.

26
Two more quotes from IPCC SROCC attached:

27
Note that these are the estimates from their 2016 study. They've since indicated that they are considerable over estimates.

There are summaries of many other studies in the chapter, including ones that address the recently discovered cavity under Thwaites Glacier.  They also address the feedbacks from huge increases in meltwater on ocean stratification.

None of the scenarios lead to the catastrophic consequences implied by AbruptSLR's musings.  All of them agree that if we can keep emissions in-line with the RCP 2.6 scenario, the future sea level rise is greatly reduced from the RCP 8.5 emissions scenarios.  Many agree (including DeConto and Pollard) that the WAIS will not collapse under the RCP 2.6 scenario.

As you cite, IPCC SROCC also refers to Kopp et al 2017 (including DeConto & Pollard) which shows a non-negligible risk of pretty fast SLR between 2100-2300 even at RCP2.6 (3m SLR in 2 centuries). See table 1 in Kopp et al attached below. When DeConto & Pollard will have published their lowered estimates for 2100, we may also learn their new estimates for 2200 and 2300, which may be even higher than before, if I've understood their earlier indications of those results correctly. None of these estimates will be as definitive as you seem to present them, which means they still imply risks that should not be ignored, as indicated by the quotes from IPCC SROCC attached below, and as ASLR fortunately does not tire of reminding us, as do experts as for example Dewi Le Bars, when he reflected last February on the implications of two recent papers for the projections by DeConto & Pollard and for ice-climate feedback modelling (as proposed by Hansen et al, amongst others):
https://sites.google.com/site/dewilebars/sea-level-monthly-review/february-2019

On Edwards et al 2019:
'The claim that MICI is "not necessary" to reproduce past sea level high stands is both not really true and not really useful. The uncertainty range about what could have been the contribution of Antarctica to sea level during the Pliocene is 5-20 m and during the Last Interglacial it is 3.6-7.4 m. DeConto and Pollard’s model without MICI can reproduce up to 6 m and 5.5 m respectively for these two period (see Edwards et al. E.D. Fig. 4). So yes it can reproduce the lower part of the ranges. But most of the Pliocene range cannot be reproduced with the no-MICI assumption. What the figure shows is that the model with MICI covers a much bigger par of the possible Antarctic contribution for these periods. And still, even including MICI, the model can only explain a maximum of 12 m contribution for the Pliocene. Which means additional mechanisms would be necessary to cover the whole range of possible Antarctic contribution for that period. The claim that MICI is “not necessary” is also not very useful practically because projections with MICI are used to make high-end sea level scenarios. The important information is then is it possible or not? If it was not possible then it would be good news and decision makers wouldn't need to take it into account. "Not necessary" only has an impact on low-end scenarios, for which MICI would already not be used anyways.'

On Golledge et al 2019:
'Current state of the art (CMIP5 type) climate models do not include ice sheet models so the coupled effects between ice sheets and climate are a blind spot. In these climate models the ice sheets are just white mountains that do not change over time. They might have a snow layer on top of them but no ice. So snow falls on them accumulate a little bit and when it melts it is put in the nearest ocean grid box. If too much accumulates then it is put directly in the ocean to avoid infinite accumulation. What is missing is a model to transform the snow to ice and then transport it back to the sides of the ice sheet or to the ocean under the force of gravity. This is what ice sheet models do. Golledge et al. use the PISM ice sheet model for Greenland and Antarctica and couple them offline to LOVECLIM, an intermediate complexity climate model. Intermediate complexity means lower resolution and simpler physics compared to CMIP5 type climate models. It is the type of models generally used for long paleoclimate simulations.

What they find is that allowing feedbacks between the ice sheets and the climate model leads to strengthen both Antarctic and Greenland mass loss, by 100% and 30% respectively. For Antarctica this is not a surprise, although the magnitude is much bigger than I expected. Freshwater from the melting of ice leads to increase the ocean stratification, because it is is very light. This reduces vertical ocean mixing and as a result the surface of the ocean cools down while the subsurface warms up. Antarctica mostly looses mass from ice shelves basal melt and calving which is strengthened by warmer subsurface ocean temperature. For Greenland, it comes as a surprise to me that the feedback would increase the mass loss, because Greenland mostly looses mass from surface melt and a cooler atmosphere temperature would tend to reduce surface melt. Unfortunately the paper does not explain the mechanisms at play there (or did I miss it?).

There are a few issues with the ice sheet models that reduce my confidence in the projections. For Greenland the model is not able to reproduce the recent fast mass loss acceleration. Therefore the authors artificially impose the mass loss on the model in two ways: (1) decrease the friction between the ice and the bed (basal traction) to have a faster flow between 2000 and 2015 and (2) reduce the snowpack refreezing between 2000 and 2025. Refreezing is important for the mass balance because on ice sheets more than half of the snow that melts in the summer refreezes locally. It never reaches the ocean. Michiel van den Broeke had a similar comments in Trouw (in Dutch). You can force the model to agree with observations but if the model does not have the proper dynamics to explain observations there is no reason it is doing a good job for the future. For Antarctica, the model starts with enormous mass accumulation (1000 Gt/year in 1900) and accumulates mass until the 1980th. This is clearly not possible, such an accumulation would have been seen by tide gauge measurements. In fact as I said in the last review it is expected that Antarctica was slowly loosing mass in the 20th century. Also, the internal variability of grounded ice is so large in the model (Fig. 1a-d) that I do not understand what is going on physically (please let me know if you do).

In conclusion, the paper’s goal is important and it is the first time that two high resolution ice sheet models are coupled to a climate model. This is a big step in the right direction. However, I am not convinced by the results because of the issues mentioned above concerning the ice sheet models. Nevertheless, it is very instructive as it shows the long way that is left for ice sheet models to reach the level at which we can trust their future projections.'

28
At current observed rates of warming (with GMSTA around 1C above pre-industrial), the oceans around Antarctica are warming at 0.05 degrees C per decade.  At that rate, it would take 400 years to hit one of the necessary triggers for MICI to start.

That may be why DeConto and Pollard are urging more caution now about the MICI models.  They are still claiming that hydrofracturing could begin as GMSTA approaches 2C above pre-industrial, but that results in centimeters of sea level rise, not meters as MICI would project.

Hansen et al 2016 write:
https://www.atmos-chem-phys.net/16/3761/2016/

"We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10–40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500–2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6–9 m with evidence of extreme storms while Earth was less than 1 °C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2 °C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50–150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments."

If this ice melt feedback indeed exists, what would this mean for the rate of warming of the subsurface ocean waters? When would this warming reach 2 degrees C above current temperatures? Have DeConto & Pollard taken this potential feedback into account? How likely or unlikely is this feedback and what level of risk does this uncertainty imply?

29
Greenland and Arctic Circle / Re: What's new in Greenland?
« on: June 21, 2019, 11:46:54 AM »
Aschwanden et al 2019 on potential Greenland ice mass loss in the coming centuries:
https://advances.sciencemag.org/content/5/6/eaav9396?fbclid=IwAR2B6SbuwJ8009PDv7YFpEeoK4xv076tCnloSI_KHIJj6GfMlKcReZEYan4

They estimate about a 16% chance that the GIS will be completely gone in no more than five centuries under RCP8.5, and about a 50% chance that this would take no more than seven centuries (see their fig 1b below).

30
Maybe not the first, being rich enough to postpone being hit before some poorer parts of the world. But we'll be hit eventually, or that risk seems substantial, at least.

31
Levermann et al 2019 draft open for discussion, on Antarctic contribution to SLR:
https://www.earth-syst-dynam-discuss.net/esd-2019-23/

"For the so-called business-as-usual warming path, RCP-8.5, we obtain a median contribution of the Antarctic ice sheet to global mean sea-level rise within the 21st century of 17 cm with a likely range (66-percentile around the mean) between 9 cm and 36 cm and a very likely range (90-percentile around the mean) between 6 cm and 59 cm. For the RCP-2.6 warming path which will keep the global mean temperature below two degrees of global warming and is thus consistent with the Paris Climate Agreement yields a median of 13 cm of global mean sea-level contribution. The likely range for the RCP-2.6 scenario is between 7 cm and 25 cm and the very likely range is between 5 cm and 39 cm. The structural uncertainties in the method do not allow an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario, separately. The rate of sea level contribution is highest under the RCP-8.5 scenario. The maximum within the 21st century of the median value is 4 cm per decade with a likely range between 2 cm/dec and 8 cm/dec and a very likely range between 1 cm/dec and 13 cm/dec."

32
Bamber et al 2019 shows results below of structured expert judgement on global sea level rise projections:
https://www.pnas.org/content/early/2019/05/14/1817205116

33
AR5 says nothing about the anthro carbon budget that causes the RCP.

"Nothing" seems overstated: see for example figure SPM.10c below from the AR5 Synthesis Report, which shows carbon budgets for different temperature targets, in line with the references made by Sleepy. On p.19 the SPM says:
"Cumulative emissions of CO2 largely determine global mean surface warming by the late 21st century and beyond. Limiting risks across RFCs would imply a limit for cumulative emissions of CO2. Such a limit would require that global net emissions of CO2 eventually decrease to zero and would constrain annual emissions over the next few decades (Figure SPM.10) (high confidence)."

34
While AbruptSLR is doing a great job in highlighting potential dangers of climate change, he is focusing on the very low-probability extreme climate change scenarios. If you read the articles he links to, they often focus on hypothetical extreme model runs to show what could happen in the case of runaway carbon emissions. He has recently posted papers with 4 times increases in CO2 concentrations and 5 or 11 times increases in methane concentrations. Those are scenarios well beyond even the extremes of RCP 8.5.
[...]
Also, renewable energy is now cheaper than coal and is quickly becoming cheaper than natural gas and EVs are poised to outsell ICEs in the coming decade. As a result, we're probably going to end up on an emissions path between RCP 2.6 and 4.5.
So there are many reasons to hope. I agree with AbruptSLR and many posters on this site that we need to get off of fossil fuels as quickly as possible and I also agree with the consensus climate scientists that it's not too late. Don't give up hope.

I never read ASLR's posts as a reason for despair. On the contrary: he shows the urgency of taking the collective action that can at this point hopefully still prevent the worst-case risks from materializing. Many mainstream communications focus on current best-estimates, without being or making people aware of the severe fat tail risks. Sutton 2018 proposes to improve on this lack of clear risk communication by using this simple figure below that shows the probability of very high climate sensitivity and its likely impacts, concluding that the highest risk is in the small, but significant chance of very high climate sensitivity and related impacts:
https://www.earth-syst-dynam.net/9/1155/2018/

Not being aware of this risk increases the chance of insufficient collective climate action (mitigation and adaptation), and would therefore increase the chance of eventual depair, in case worst-case scenario's would turn into reality. Since we don't know the real probability distribution for sure, we're in a situation of deep uncertainty, which makes strong climate action all the more urgent as a precaution against finding out that a high climate sensitivity appears to be more likely than mainstream science thought so far.

35
Reading some of Radoslav Dimitrov's articles on the UN FCCC processes (he was a delegate at Copenhagen and Paris) helps show what a political circus it is. He calls the Copenhagen Accord and Paris Agreement "decoy institutions" meant to hide the reality of a lack of any real progress.

Thanks for the reference to Dimitrov. It seems he indeed calls the Copenhagen Accord a decoy institution, but leaves the question open on the Paris Agreement (Dimitrov 2018):
https://www.researchgate.net/profile/Radoslav_Dimitrov/project/Decoy-institutions-in-world-politics/attachment/5ba286483843b006753a259a/AS:672625667887109@1537377864774/download/+Decoy+Institutions+-R.+Dimitrov.pdf?context=ProjectUpdatesLog

"Is the Paris Agreement on Climate Change, for instance, a decoy institution? The agreement is characterized by remarkable complexity and is not a conventional treaty that conforms easily to the traditional model of international law. It relies on a complex mix between legally binding obligations and voluntary provisions that give full discretion to governments. This ambiguity leads to various interpretations and vigorous debates but, mostly, genuine uncertainty in academic circles. Some observers claim there are no legal obligations for action, and even decry it as a misleading nonbinding agreement that is camouflaged as a treaty. Others disagree and insist the Paris Agreement is a treaty with real policy obligations. Even veteran IR scholars of global governance appear at a loss and state cautiously that the vagueness of the Paris Agreement creates uncertainty about its effectiveness. The possibility that this treaty is actually an elaborate decoy institution that allows governments to hide behind a weak international arrangement could clarify the situation and deserves investigation."

In 2016 he did seem to think the Paris Agreement was a genuine diplomatic success:
http://politicalscience.uwo.ca/people/faculty/full-time_faculty/GEP%20Paris%20Agreement.pdf

"The Paris Agreement constitutes a political success in climate negotiations and traditional state diplomacy, and offers important implications for academic research. Based on participatory research, the article examines the political dynamics in Paris and highlights features of the process that help us understand the outcome. It describes battles on key contentious issues behind closed doors, provides a summary and evaluation of the new agreement, identifies political winners and losers, and offers theoretical explanations of the outcome. The analysis emphasizes process variables and underscores the role of persuasion, argumentation, and organizational strategy. Climate diplomacy succeeded because the international conversation during negotiations induced cognitive change. Persuasive arguments about the economic benefits of climate action altered preferences in favor of policy commitments at both national and international levels."

36
I think, telling us this, is the whole purpose of this thread, isn't it AbruptSLR?

It doesn't have to be the purpose, but could be a consequence/conclusion.

37
Some interesting reflections by Dewi Le Bars on the implications of two recent papers for the projections by DeConto & Pollard and for ice-climate feedback modelling (as proposed by Hansen et al, amongst others):
https://sites.google.com/site/dewilebars/sea-level-monthly-review/february-2019

On Edwards et al 2019:
'The claim that MICI is "not necessary" to reproduce past sea level high stands is both not really true and not really useful. The uncertainty range about what could have been the contribution of Antarctica to sea level during the Pliocene is 5-20 m and during the Last Interglacial it is 3.6-7.4 m. DeConto and Pollard’s model without MICI can reproduce up to 6 m and 5.5 m respectively for these two period (see Edwards et al. E.D. Fig. 4). So yes it can reproduce the lower part of the ranges. But most of the Pliocene range cannot be reproduced with the no-MICI assumption. What the figure shows is that the model with MICI covers a much bigger par of the possible Antarctic contribution for these periods. And still, even including MICI, the model can only explain a maximum of 12 m contribution for the Pliocene. Which means additional mechanisms would be necessary to cover the whole range of possible Antarctic contribution for that period. The claim that MICI is “not necessary” is also not very useful practically because projections with MICI are used to make high-end sea level scenarios. The important information is then is it possible or not? If it was not possible then it would be good news and decision makers wouldn't need to take it into account. "Not necessary" only has an impact on low-end scenarios, for which MICI would already not be used anyways.'

On Golledge et al 2019:
'Current state of the art (CMIP5 type) climate models do not include ice sheet models so the coupled effects between ice sheets and climate are a blind spot. In these climate models the ice sheets are just white mountains that do not change over time. They might have a snow layer on top of them but no ice. So snow falls on them accumulate a little bit and when it melts it is put in the nearest ocean grid box. If too much accumulates then it is put directly in the ocean to avoid infinite accumulation. What is missing is a model to transform the snow to ice and then transport it back to the sides of the ice sheet or to the ocean under the force of gravity. This is what ice sheet models do. Golledge et al. use the PISM ice sheet model for Greenland and Antarctica and couple them offline to LOVECLIM, an intermediate complexity climate model. Intermediate complexity means lower resolution and simpler physics compared to CMIP5 type climate models. It is the type of models generally used for long paleoclimate simulations.

What they find is that allowing feedbacks between the ice sheets and the climate model leads to strengthen both Antarctic and Greenland mass loss, by 100% and 30% respectively. For Antarctica this is not a surprise, although the magnitude is much bigger than I expected. Freshwater from the melting of ice leads to increase the ocean stratification, because it is is very light. This reduces vertical ocean mixing and as a result the surface of the ocean cools down while the subsurface warms up. Antarctica mostly looses mass from ice shelves basal melt and calving which is strengthened by warmer subsurface ocean temperature. For Greenland, it comes as a surprise to me that the feedback would increase the mass loss, because Greenland mostly looses mass from surface melt and a cooler atmosphere temperature would tend to reduce surface melt. Unfortunately the paper does not explain the mechanisms at play there (or did I miss it?).

There are a few issues with the ice sheet models that reduce my confidence in the projections. For Greenland the model is not able to reproduce the recent fast mass loss acceleration. Therefore the authors artificially impose the mass loss on the model in two ways: (1) decrease the friction between the ice and the bed (basal traction) to have a faster flow between 2000 and 2015 and (2) reduce the snowpack refreezing between 2000 and 2025. Refreezing is important for the mass balance because on ice sheets more than half of the snow that melts in the summer refreezes locally. It never reaches the ocean. Michiel van den Broeke had a similar comments in Trouw (in Dutch). You can force the model to agree with observations but if the model does not have the proper dynamics to explain observations there is no reason it is doing a good job for the future. For Antarctica, the model starts with enormous mass accumulation (1000 Gt/year in 1900) and accumulates mass until the 1980th. This is clearly not possible, such an accumulation would have been seen by tide gauge measurements. In fact as I said in the last review it is expected that Antarctica was slowly loosing mass in the 20th century. Also, the internal variability of grounded ice is so large in the model (Fig. 1a-d) that I do not understand what is going on physically (please let me know if you do).

In conclusion, the paper’s goal is important and it is the first time that two high resolution ice sheet models are coupled to a climate model. This is a big step in the right direction. However, I am not convinced by the results because of the issues mentioned above concerning the ice sheet models. Nevertheless, it is very instructive as it shows the long way that is left for ice sheet models to reach the level at which we can trust their future projections.'

38
Kent A. Peacock (12 Sep 2018) "A Different Kind of Rigor: What Climate Scientists Can Learn from Emergency Room Doctors", Ethics, Policy & Environment, Volume 21, 2018 - Issue 2, Pages 194-214, https://doi.org/10.1080/21550085.2018.1509483
https://www.tandfonline.com/doi/full/10.1080/21550085.2018.1509483

Peacock says:
"There is a genuine possibility, however, remote, that the whole contents of the Bentley trench could shatter in a matter of weeks or months, raising global mean sea level by 3 m or more almost immediately."

What peer-reviewed publication supports this statement? I think Pollard, DeConto & Alley 2015 have said they can't rule out this is possible in a matter of "decades" (3m in 3 decades?):
https://www.sciencedirect.com/science/article/pii/S0012821X14007961

"In summary, applying a simple Pliocene-like warming scenario to our model, the combined mechanisms of MISI, melt-driven hydrofracturing and cliff failure cause a very rapid collapse of West Antarctic ice, on the order of decades."

I have not seen "weeks or months". Anyone else?

39
indeed the current rate of CO₂ emissions is somewhere to 10 to 15 time the rate during the PETM (depending on which part of the PETM we compare to add whether we consider CO₂-equiv emission rates)

Scanning several papers on the PETM again I see estimates on the rate of emissions and warming vary significantly, so it's hard to have much confidence in any particular estimate, whether it was 10x slower than currently, 100x slower, or maybe even as fast as currently.

As Turner 2018 concludes:
https://royalsocietypublishing.org/doi/full/10.1098/rsta.2017.0082

"After more than 25 years of intense study, the PETM continues to be the best analogue for future CO2-driven global warming. However, the aspect of the PETM that is most relevant for understanding future impacts—the duration of carbon release—is extremely challenging to constrain using the typical methods for determining age in the geologic record (biomagnetostratigraphy and cyclostratigraphy). Combined data and modelling studies offer a potential way forward by suggesting simulacra of the traces left in the geologic record that indicate a short carbon input duration. Each of the age-model independent methods outlined here has caveats in its application; however, a consensus appears to be emerging that the carbon emissions that drove the CIE occurred over just a few thousand years. This still suggests emissions rates about 10× slower than the current annual average, but is similar to predicted rates of additional carbon release from natural carbon cycle feedbacks..."

However, 10x slower emissions 56 million years ago when CO2 levels were higher to begin with and the sun was somewhat weaker than now implies CO2-forcing is currently already probably substantially more than 10x stronger than during the PETM, and rising fast as long as we don't eliminate our emissions. What that does to ECS humanity will find out in coming decades and centuries, assuming there will be humans around and they will still be able to determine ECS.

40
the current high rate of anthropogenic radiative forcing (at least 100 times faster than during the PETM)

This may well happen later this century, but currently it seems more like 10x faster than during the PETM, according to Diffenbaugh & Field 2013 (see attachments below):
http://denning.atmos.colostate.edu/readings/Impacts/Ecosystems.Science-2013-Diffenbaugh-486-92.pdf

Such fast warming may indeed cause ECS to increase to levels that are higher than the natural ECS at the same temperature in the past, as far as I know (I would have to look for specific references).

41
Anyone has access to the full text?

They're talking about quite warm climates:
https://sci-hub.tw/https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JD029262

"ECS for the first three CO2 doublings beyond the present day Earth (up to 2880 μbar CO2) fall within the IPCC estimated range, with values of 3.8 K, 4.0 K, and 4.1 K respectively (gray box in Figure 1b). At the 4th CO2 doubling (5760 μbar CO2) ECS exceeds the IPCC estimated range, reaching 5.8 K. Thus, the sensitivity of climate accelerates under potential anthropogenic CO2 increases, in agreement with recent studies [Meraner et al., 2013; Russell et al., 2013; Caballero and Huber, 2013]. We find a sharp maximum in ECS of 16.0 K evident at the 6th CO2 doubling (0.02304 bar CO2) beyond present day Earth conditions... warming climate leads to reductions in the cloud albedo, thus constituting a positive climate feedback and leading to further warming. The sharp transition between temperate and moist greenhouse climate states centered at Ts ~ 320 K is associated with the minima in cloud albedo"

42
I wish I could :)

43
There is not yet a compelling theory for the magnetic field or magnetic polar wander. There is almost certainly a coupling between the location of the spin axis and the magnetic poles, but the nature of this coupling is not understood, probably because the nature of the magnetic field is not well understood. There is a Nobel waiting for anyone who comes up with answers.

Could small changes in the position of the spin axis maybe cause changes in convection in the outer core, and could those in turn cause (small) changes in the position of the magnetic pole, as one factor amongst others?

Here someone says:
http://all-geo.org/highlyallochthonous/2008/03/where-the-earths-magnetic-field-comes-from/
“Earth’s rotation… has a strong influence on the patterns of convection in the outer core. Most significantly, it has a tendency to produce helical convection currents which align with the spin axis…”.

The geographical pole apparently moves partly due to convection in the Earth mantle:
https://phys.org/news/2018-09-scientists-id-earth-axis-drift.html
“Using observational and model-based data spanning the entire 20th century, NASA scientists have for the first time identified three broadly-categorized processes responsible for this drift—contemporary mass loss primarily in Greenland, glacial rebound, and mantle convection... Mantle convection is responsible for the movement of tectonic plates on Earth’s surface. It is basically the circulation of material in the mantle caused by heat from Earth’s core. Ivins describes it as similar to a pot of soup placed on the stove. As the pot, or mantle, heats, the pieces of the soup begin to rise and fall, essentially forming a vertical circulation pattern—just like the rocks moving through Earth’s mantle.”

Or is this hypothesis too farfetched?

44
Whether the acceleration in magnetic polar wander shown in the first attached image (from Nature 2019) is related to the high magnetic anomaly in the South Atlantic, see the second image (and Replies #113, #115 & #117), and thus possibly to Antarctic ice mass loss, is a matter worth investigating.

Maybe this could contribute to an explanation:
http://advances.sciencemag.org/content/2/4/e1501693

“We analyze space geodetic and satellite gravimetric data for the period 2003–2015 to show that all of the main features of polar motion are explained by global-scale continent-ocean mass transport. The changes in terrestrial water storage (TWS) and global cryosphere together explain nearly the entire amplitude (83 ± 23%) and mean directional shift (within 5.9° ± 7.6°) of the observed motion. We also find that the TWS variability fully explains the decadal-like changes in polar motion observed during the study period, thus offering a clue to resolving the long-standing quest for determining the origins of decadal oscillations. This newly discovered link between polar motion and global-scale TWS variability has broad implications for the study of past and future climate.”

The Nature article doesn't seem to mention this possibility?

45
Thanks for the Rob DeConto presentation of March 30th 2018, ASLR.
From 56m-66m I find particularly interesting, where he talks about (quite arbitrary) speed limits for cliff failure in his model, and stretching these limits in newer versions, as yet unpublished, if I understand correctly. Also atmospheric modelling would seem to slow melt in the first decades (compared to an earlier version), but cliff failure could speed it up more later, it seems from what he says here.

46
Good to see you back, ASLR!

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