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Emergent constraints on TCR and ECS from historical warming in CMIP5 and CMIP6 models

Reposted from Dr. Judith Curry’s Climate Etc.

Posted on August 19, 2020 by niclewis

By Nic Lewis

This is a brief comment on a new paper[i] by a mathematician in the Exeter Climate Systems group, Femke Nijsse, and two better known colleagues, Peter Cox and Mark Williamson. I note that Earth Systems Dynamics published the paper despite one of the two peer reviewers recommending against acceptance without further major revisions. But neither of the reviewers appear to have raised the issue that I focus on here.

“Emergent constraints” methods relate observable climate trends, variations or other variables to climate system properties of interest, such as equilibrium climate sensitivity (ECS), in an ensemble of models. They then use the observed values of the variable(s) involved to estimate ECS or the other properties of interest. I’m not a great fan of emergent constraints studies, the results of which are often sensitive to the model ensemble used. Here the emergent constraint is the relationship, assumed linear, between transient climate response (TCR) and global warming from 1975 onwards.

The authors thereby derive, from a combined CMIP5 and CMIP6 54 model ensemble  a TCR estimate of 1.68 K (16-84% ‘likely’ range 1.29–2.05 K) using warming up to 2019.  Unfortunately, the study does not provide a results table for their TCR estimates and the 5-95% TCR range is not stated.

The paper states that using instead warming up to 2014, thereby enabling use of a larger set of CMIP6 models, reduces the TCR estimate to 1.54 K (5-95% range 0.76–2.30 K), but don’t mention that in their abstract or conclusions.

The authors also derive an estimated likely range for ECS of 1.9–3.4 K (5–95% range 1.5–4.0 K) from CMIP6 models, median estimate 2.6 K, from warming to 2019. Based on warming up to 2014 in the larger ensemble of CMIP6 models, the median ECS estimate is 1.9 K (5–95% range 1.0–3.3 K). Again, the result from the larger ensemble is not mentioned in the abstract or conclusions.

I am very doubtful about estimating ECS by comparing observed and simulated historical warming. Without also using observational data on ocean heat update, to estimate changes in the Earth’s energy imbalance, it is impossible to distinguish satisfactorily between ECS and ocean heat uptake both being high and them both being low – either combination can produce the same historical warming. So I would not place any reliance on their ECS ranges, even if they don’t look unreasonable.

On the other hand, one would expect historical warming in climate models to have a close to linear relationship with their TCR, since pre-1975 ‘warming in the pipeline’ is fairly negligible and post 1975 forcing is reasonably close to the quasi-linear ramp forcing used to measure TCR, and similarly of multidecadal length. The existence of episodic volcanic forcing, to which models and the real climate system may respond differently, is a possible confounding factor, although use of the difference between 1975–1985 and the 2009–2019 means to measure warming excludes years affected by the 1991 Mount Pinatubo eruption. There is also the issue that the mean change in effective radiative forcing (ERF) in climate models between those two periods may not equal the ERF change in the real climate system. For CMIP5 models at least, I suspect that their mean ERF change falls somewhat short of the actual change.  That would induce an upwards bias in the emergent constraint TCR estimate.

Regardless of the above considerations, there is a fatal problem with the regression method used to relate TCR with warming. If a model has a TCR of zero, then it would be expected to show zero historical warming. The authors appear to recognise this, writing “As no warming would be expected if climate sensitivity were zero, we expect the regression to pass through the intercept”. They actually mean pass through the origin (have a zero y-intercept), as their equations (A3) and (A4) make clear. And their equation (3) theoretical relationship between TCR and warming, TCR = s ΔT, has no offset term. It is therefore physically inappropriate to use regression with a y-intercept term being estimated.

However, despite admitting that a zero y-intercept is physically appropriate, the study estimates a regression fit using a y-intercept as well as a slope coefficient parameter. Moreover, the resulting best-fit line does not pass at all close to the origin. Their estimate implies that climate models with a TCR of ~0.7 K would have simulated zero post-1975 warming. Their Figure 4(a), reproduced as Figure 1 below, shows this.

Figure 1. Reproduction of Figure 4(a) of Nijsse et al. (2020). Emergent constraint on TCR against historical warming ΔT . ΔT is calculated from the difference between 1975–1985 and 2009–2019 of a time series of GMSAT. Linear regression is performed with all CMIP5 and CMIP6 simulations. Shaded areas indicate a 90% prediction interval. The vertical dashed line is the mean value of the observations, and the y axis shows the probability distribution of both generations of ensembles.

A quite involved and not very clearly described hierarchical Bayesian model regression method is used, which makes it difficult to reproduce exactly the study’s results. Remarkably, the numerical value and uncertainty range of the observed warming estimate is nowhere stated. I therefore measured it off their Figure 4(a), as 0.606 K, and took the shading as showing a normally distribution 5–95% range, width 0.225 K. Based on a simple ordinary least squares (OLS) with-intercept regression of TCR on model-ensemble mean simulated historical warming, across the multimodel combined CMIP5 and CMIP6 ensemble, I estimate a median TCR estimate of 1.62 K, marginally lower than their 1.68 K.

If I repeat the exercise but without estimating a y-intercept, thereby forcing the regression fit to match a zero TCR with zero historical warming, the emergent constraint gives a TCR best estimate of 1.43 K. The regression fit is very good (R2 = 0.97). There is little regression dilution when no y-intercept  is estimated. Regressing warming on TCR rather than vice versa gives an emergent constraint TCR best estimate of 1.47 K. Regressing TCR on warming just across the CMIP5 ensemble gives a slightly lower TCR estimate of 1.37 K (R2 = 0.97). Doing so across the CMIP6 ensemble alone gives a TCR estimate of 1.50 K ((R2 = 0.98). The slope coefficient standard errors imply that there is only a 3.1% chance that the TCR–warming relationship is the same in the CMIP5 and CMIP6 ensembles.

It is unclear which regression method is more accurate. Using the geometrical mean of the estimates regressing each way, as is sometimes recommended, gives a TCR best estimate of 1.45 K from the combined CMIP5/CMIP6 ensemble. A crude estimate of uncertainty can be obtained by using, for each type of regression, the standard error in the slope estimate and the observational uncertainty to form a large number of randomly sampled TCR estimates, combining the two resulting sets of estimates and computing quantiles. Doing so gives a median TCR estimate of 1.45 K, with a 16–84% range of 1.29–1.62 K and a 5–95% range of 1.18–1.74 K. However, this does not account for all sources of uncertainty.

Interestingly, when fitting a relationship between ECS and post-1975 warming, and between ECS and TCR, the authors didn’t use a y-intercept term, resulting in those fits passing through the origin.

My key point is that an analysis method that results in a physically reasonable estimated relationship between the variables being studied should be used. An estimated relationship that implies zero warming with a positive TCR, and significant cooling with a zero TCR, is unphysical. Therefore, the results of the Nijsse et al. paper are unreliable and should be discounted.

Nicholas Lewis                                                           19 August 2020


[i] Njisse et al., 2020: Emergent constraints on transient climate response (TCR) and equilibrium climate sensitivity (ECS) from historical warming in CMIP5 and CMIP6 models, Earth Syst. Dynam., 11, 737–750, 2020 https://doi.org/10.5194/esd-11-737-2020

Originally posted here, where a pdf copy is also available

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August 20, 2020 at 04:16PM

More Hate for Less Heat

The Center for Countering Digital Hate (CCDH) is a non-governmental organisation devoted to Strengthening communities and democracy by disrupting identity-based hate and dangerous misinformation in digital spaces.”It’s British based (despite the spelling of its name) and, since the setting up of its website blog in May, has been largely concerned with countering mis-information on the coronavirus epidemic. Nothing wrong with that, one might think. No doubt much dangerous mis-information is out there – at fake news sites like the Lancet, for example, or the New England Journal of Medicine. It’s dirty work tracking it down, but someone’s got to do it. But what’s “identity-based hate” got to do with it?

Of the seven articles which have appeared on their blog since its opening in May 2020, four deal with the virus and three with various aspects of racism. These are important subjects of course, but again, it’s difficult to see how the Center’s aim of disrupting identity-based hate and dangerous misinformation in digital spaces”is furthered by an article like this one – “Domestic actors trump foreign influence in polarising Black Lives Matter debate” which begins:

It is now well established that foreign actors, particularly Russia, have sought to spread online misinformation that stokes political and racial divisions.

The sole source for this statement is an article at Wired about the activities of the Russian “Internet Research Agency” in 2016, ands the sole source for the Wired article is a report by the US Senate Intelligence Committee. Later on, the accusation that “Russia is up to its old tricks” over the George Floyd protests is supported by a link to an article at Business Insider, which quotes“a former chief information officer of the White House?” If all the CCDH can come up with as support for its position is a Senate report and a quote from an ex-White House official, then what’s the “Non-” in “Non-Governmental Organisation” for?

The article goes on to argue that, though Russia is spreading “online misinformation that stokes political and racial divisions,”most of the harm is done by local influencers. It notes, for instance, that:

Video footage of a protester scaling the Cenotaph and attempting to burn the British flag was watched 26,000 times when posted by RT, the UK television channel owned by the Russian state. But the same footage tweeted by Katie Hopkins received ten times that number of views.

– a wholly unsurprising finding. But where’s the identity-based hate?” Where’s the dangerous misinformation?” RT is a state-financed television channel, just like the BBC. They didn’t lie, they didn’t break any laws, yet somehow their absolutely normal news reporting is being assimilated to the shady actions of Russian bot factories allegedly spreading hate.

In fact, there’s very little evidence at their site that the CCDH is doing much to counter digital hate at all. They were founded in December 2017, but their blog only goes back to May 2020. So what are they up to? Let them speak for themselves:

The Center for Countering Digital Hate is an international not-for-profit NGO that seeks to disrupt the architecture of online hate and misinformation […] The Center’s solutions have proven effective against a number of different types of hate and misinformation, like identity-based hate, climate change denial and health misinformation.

They also run this site set up in 2019, whose “Briefing” page has a list of media outlets which CCDH wants to defund, and, if possible, eliminate. Among them is Breitbart, which CCDH accuses of having “promoted debunked climate denialism.” The source for this accusation is a tweet by SFFakeNews which says “Breitbart publishes racist, sexist, Islamophobic, homophobic Fake News and climate denialism..”

Another of their targets is TR News, set up by racist agitator Tommy Robinson. One of four accusations against this site is that:

They used misinformation to try to suggest the Australian bushfires were not caused by climate change.

In support of which CCDH again cite their own tweets, saying:

The article and video in question argues that arsonists, not the climate crisis, is causing the extreme fires. It claims that 200 people are facing charges in New South Wales alone. This is false […] Victoria Police rejects social media campaign claiming arson caused fires…

That New South Wales is not Victoria seems to have escaped the notice of the CCDH fake news sleuth, but let’s not dive headfirst down that wallaby hole. Let’s just note how odd it is that one of the main charges against the unpleasant and insignificant Tommy Robinson is that his opinion on the cause of Australian bush fires doesn’t accord with that of the Guardian.

CCDH also does science, for instance with this article:”Unregulated social media poses a threat to public health” Guest post by Dr Daniel Allington

We know that health-related misinformation and conspiracy theories are very popular on social media… We also know that belief in conspiracy theories is associated with reduced engagement in health-protective behaviours, from safer sex and vaccination to hand-washing and lockdown compliance. Now new research, carried out by myself and colleagues at King’s College London, shows that relying on social media for information about COVID-19 is in itself associated with failure to follow public health guidance intended to limit the spread of COVID-19… We found that people who rely more heavily on social media for information about COVID-19 are more likely to believe in COVID-19 conspiracy theories, and that people who believe in COVID-19 conspiracy theories are less likely to be washing their hands more often and socially distancing. Beyond that, we also found that people who rely more heavily on social media for information about COVID-19 are less likely to be washing their hands more often and socially distancing, while people who rely more heavily on television and radio for information are more likely to be doing so… Let that sink in. Getting health information from social media is bad for you.

In other words, conspiracists read blogs, and they don’t wash their hands after.

Dr Allington’s paper is available here. As with most articles of this sort, the raw results of their surveys are not in the article but buried in the supplementary material, available here.

By Dr Allington’sown argument, the fact that he’s publicising his crap research on social media is evidence that it’s tainted by conspiracy theorising, and therefore bollocks. Which it is, but not for that reason. Dr Allington believes that the theories that the virus came from a lab, or that the symptoms are caused by the 5G network, are conspiracy theories. Like, you know, the Chinese deliberately let the virus leak out, and the 5G network was deliberately set up to kill the elderly.

Dr Allington is obviously steeped in this kind of fake news only available on Russian-bot-infested blogs. And he’s probably not washing hishands as often as he should either. How dare he.

Please note that that’s his conclusion, not mine. I judge an argument on its merits, not on where it appears. In this I’m not like Dr Allington, or his readers at CCDH, if he has any. And nor are most of the readers of this blog, I‘d guess. But I’ll wager we wash our hands just as often as he does. Why not do a survey among us to check it out?

There’s more to say about the Allington article, but this post is already too long. Do I hate The Center for Countering Digital Hate? Not really. At least, not digitally. Despite my occasional outbursts of blind fury against the numerous fascistic pseudo-leftist Orwellian sites that want to corral us with the Tony Robinsons of the world, I’m basically a live-and-let-live kind of person. But are they? And the weirdoes who finance them? And Cambridge University Press which publishes Dr Allington’s mindless burblings? Who are these people? And what do they want us climate sceptics to do exactly, in order not to be the target of their anti-hate campaign?

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August 20, 2020 at 03:20PM

The Marxists have forced out the Conservatives, now they’re coming for the Liberals

Some thought provoking insights from Yoram Hazony in The Challenge Of Marxism. I’m not inclined to read analysis of anything Marxist, but this moment in history has some uncanny similarities I was not aware of, and Hazony connects the dots from Karl to Kamala (so to speak). He paints a compelling pattern, even if I want to add details and patterns myself. It’s a springboard…

Read it all.

The Marxists have forced out the Conservatives, now the wheel has turned and  they’re coming for the Liberals, argues Hazony. The Liberal world thought they were marching through the institutions but the momentum was with the Marxists among them, who have now forged ahead and are turning on their own.

Will the liberals drop their liberalism and adopt marxism, or will they push back?

 Anti-Marxist liberals are about to find themselves in much the same situation that has characterized conservatives, nationalists, and Christians for some time now: They are about to find themselves in the opposition.

This means that some brave liberals will soon be waging war on the very institutions they so recently controlled. They will try to build up alternative educational and media platforms in the […]Rating: 10.0/10 (1 vote cast)

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August 20, 2020 at 02:14PM

Fossil leaves show high atmospheric carbon spurred ancient ‘global greening’

A unique New Zealand deposit opens insights into how modern climate change may proceed

EARTH INSTITUTE AT COLUMBIA UNIVERSITY

IMAGE
IMAGE: A 23-MILLION-YEAR-OLD LEAF PRESERVED IN A ONETIME NEW ZEALAND LAKE BED, KEY TO PAST ATMOSPHERIC CONDITIONS. ONE CAN SEE VEINS, GLANDS ALONG THE TEETH, AND HOLES GNAWED BY INSECTS, WITH… view more CREDIT: JENNIFER BANNISTER/UNIVERSITY OF OTAGO

Scientists studying leaves from a 23-million-year-old forest have for the first time linked high levels of atmospheric carbon dioxide with increased plant growth, and the hot climate off the time. The finding adds to the understanding of how rising CO2 heats the earth, and how the dynamics of plant life could shift within decades, when CO2 levels may closely mirror those of the distant past.

Scientists retrieved the leaves from a unique onetime New Zealand lake bed that holds the remains of plants, algae, spiders, beetle, flies, fungi and other living things from a warm period known as the early Miocene. Scientists have long postulated that CO2 was high then, and some plants could harvest it more efficiently for photosynthesis. This is the first study to show that those things actually happened in tandem. The findings were published this week in the journal Climate of the Past.

“The amazing thing is that these leaves are basically mummified, so we have their original chemical compositions, and can see all their fine features under a microscope,” said lead author Tammo Reichgelt, an adjunct scientist at Columbia University’s Lamont-Doherty Earth Observatory and assistant professor of geosciences at the University of Connecticut. “Evidence has been building that CO2 was high then, but there have been paradoxes.”

The so-called “carbon fertilization effect” has vast implications. Lab and field experiments have shown that when CO2 levels rise, many plants increase their rate of photosynthesis, because they can more efficiently remove carbon from the air, and conserve water while doing so. Indeed, a 2016 study based on NASA satellite data shows a “global greening” effect mainly due to rising levels of manmade CO2 over recent decades; a quarter to a half of the planet’s vegetated lands have seen increases in leaf volume on trees and plants since about 1980. The effect is expected to continue as CO2 levels rise.

This might seem like good news, but the reality is more complex. Increased CO2 absorption will not come close to compensating for what humans are pouring into the air. Not all plants can take advantage, and among those who do, the results can vary depending on temperature and availability of water or nutrients. And, there is evidence that when some major crops photosynthesize more rapidly, they absorb relatively less calcium, iron, zinc and other minerals vital for human nutrition. Because much of today’s plant life evolved in a temperate, low-CO2 world, some natural and agricultural ecosystems could be upended by higher CO2 levels, along with the rising temperatures and shifts in precipitation they bring. “How it plays out is anyone’s guess,” said Reichgelt. “It’s another layer of stress for plants. It might be great for some, and horrible for others.”

The deposit is located in a small, long-extinct volcanic crater now located on a farm near the southern New Zealand city of Dunedin. The crater, about a kilometer across, once held an isolated lake where successive layers of sediments built up from the surrounding environment. The feature was recognized only within about the last 15 years; scientists dubbed it Foulden Maar. Recognizing it as a scientific gold mine, they have been studying it ever since. Some have also been fighting an actual mining company that wants to strip the deposit for livestock feed.

In the new study, the researchers took samples from a 2009 drill core that penetrated 100 meters to near the bottom of the now-dry lake bed. Larded in between whitish annual layers of silica-rich algae that bloomed each spring for 120,000 years are alternating blackish layers of organic matter that fell in during other seasons. These include countless leaves from a subtropical evergreen forest. They are preserved so perfectly that scientists can see microscopic veins and stomata, the pores by which leaves take in air and concurrently release water during photosynthesis. Unlike most fossils, the leaves also retain their original chemical compositions. It is the only such known deposit in the Southern Hemisphere, and far better preserved than the few similar ones known from the north.

The Miocene has long been a source of confusion for paleoclimate researchers. Average global temperatures are thought to have been 3 to 7 degrees C hotter than today, and ice largely disappeared at the poles. Yet many proxies, mainly derived from marine organisms, have suggested CO2 levels were only about 300 parts per million-similar to those of preindustrial human times, and not enough to account for such warming. With evidence of high CO2 elusive, scientists have speculated that previous proxy measurements must be off.

Based on the new study and a related previous one also at Foulden Maar, the researchers were able to get at this conundrum. They analyzed the carbon isotopes within leaves from a half-dozen tree species found at various levels in the deposit. This helped them zero in on the carbon content of the atmosphere at the time. They also analyzed the geometry of the leaves’ stomata and other anatomical features, and compared these with modern leaves. By combining all the data into a model, they found that atmospheric CO2 was not 300ppm, but about 450-a good match for the temperature data. Second, they showed that the trees were super-efficient at sucking in carbon through the stomata, without leaking much water through the same route-a factor that all plants must account for. This allowed them to grow in marginal areas that otherwise would have been too dry for forests. The researchers say this higher efficiency was very likely mirrored in forests across the northern temperate latitudes, with their far greater landmasses.

Human emissions have now pushed CO2 levels to about 415 parts per million, and they will almost certainly reach 450 by about 2040-identical to those experienced by the Foulden Maar forest. Estimates of the resulting temperature increases over decades and centuries vary, but the new study suggests that most are in the ballpark.

“It all fits together, it all makes sense,” said study coauthor William D’Andrea, a paleoclimate scientist at Lamont-Doherty. In addition to showing how plants might react directly to CO2, “this should give us more confidence about how temperatures will change with CO2 levels,” he said.

Study coauthor Daphne Lee, a paleontologist at New Zealand’s University of Otago, led the charge to study Foulden Maar’s rich ecosystem after it came to light. More recently, she became an unexpected defender of the maar, when a company with owners in Malaysia and the United Kingdom announced plans to strip-mine the deposit for use as a feed additive for for pigs, ducks and other intensively farmed animals. With many more discoveries probably to be made, scientists were horrified, and allied themselves with locals who feared noise and dust. The Dunedin city council is now looking into buying the land to protect it.

###

The study was also coauthored by Ailín del Valdivia-McCarthy, a former intern at Lamont-Doherty; Bethany Fox of the University of Huddersfield; Jennifer Bannister of the University of Otago; John Conran of the University of Adelaide; and William Lee of the University of Auckland.

The paper, ‘Elevated CO2 increased leaf-level productivity and water use efficiency in the early Miocene,’ can be obtained from the authors or media@egu.eu.

Scientist contacts:

Tammo Reichgelt tammo.reichgelt@uconn.edu
William D’Andrea dandrea@ldeo.columbia.edu

More information: Kevin Krajick, Senior editor, science news, The Earth Institute kkrajick@ei.columbia.edu 212-854-9729

Lamont-Doherty Earth Observatory is Columbia University’s home for Earth science research. Its scientists develop fundamental knowledge about the origin, evolution and future of the natural world, from the planet’s deepest interior to the outer reaches of its atmosphere, on every continent and in every ocean, providing a rational basis for the difficult choices facing humanity. http://www.ldeo.columbia.edu | @LamontEarth

The Earth Institute, Columbia University mobilizes the sciences, education and public policy to achieve a sustainable earth. http://www.earth.columbia.edu.

From EurekAlert!

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August 20, 2020 at 12:51PM

Are California’s Heatwaves Getting Worse?

By Paul Homewood

California is supposed to be experiencing a record heatwave, of which Death Valley is just one example.

image

https://www.latimes.com/california/story/2020-08-18/california-heat-wave-brings-extreme-weather-and-a-glimpse-at-our-future-with-climate-change

Naturally the likes of the Guardian only want to tell you about temperatures in big cities or the airport at Stockton:

image

https://www.theguardian.com/us-news/2020/aug/17/death-valley-temperature-rises-to-544c-possibly-the-hottest-ever-reliably-recorded

But what do stations relatively unaffected by UHI tell us?

Four years ago I analysed nine long term, high quality USHCN sites, none of which showed any upward trend in summer high temperatures. They pretty much cover all of California, so should give a good representation of the state as a whole. One incidentally was Lemon Cove, which I used as an example this week.

Below are CLIMOD charts for the others, showing the highest temperature recorded each summer. They range broadly from north to south, with Orland, for instance, north of Sacramento, and Redlands down towards Palm Springs. One station, Davis, has no data on CLIMOD.

Underneath each chart is the highest temperature recorded this week, though some stations have not been updated yet – If I remember, I’ll update next month!

chart-3

Aug 2020 max – 108F

chart-4

N/A

chart-7

Aug 2020 max – 110F

chart-5

N/A

chart-6

Aug 2020 max – 112F

chart

Aug 2020 max – 109F

chart-8

N/A

In no case is this week’s peak temperature, where available, in any way unusual. Nor have  summer high temperatures been trending upwards.

I have just one more chart to show you, and I’ll use Lemon Cove again. This one plots the number of days above 100F each year:

chart-9

We can see a gradual rise from the 1960s, but recent years still don’t hit the peaks seen in the 1930s and 40s.

This is a good indicator of the duration of heat waves, and along with the summer high temperature data shows that heatwaves in California are no more severe than they have been in the past.

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August 20, 2020 at 12:42PM