Climate

Earth Is Heating Faster Than We Realized, Making 2°C Limit For Global Warming More Urgent

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A major new study finds that “scientists may have hugely underestimated the extent of global warming because temperature readings from southern hemisphere seas were inaccurate.” In short, as New Scientist puts it, “it’s worse than we thought.”

This study is the umpteenth nail in the coffin to the notion we can weaken or replace the 2°C limit for global warming as a basis for climate change policy, which was the central argument of a Nature Comment last week, titled, “Ditch the 2°C warming goal.” I and others strongly disputed that Comment by David Victor and Charles Kennel, and Victor has now offered a tortuous defense on the New York Times blog, DotEarth.

There is a solid scientific basis for concluding that humanity should be working as hard as possible to keep total warming under 2°C. And no obviously superior metric to 2°C has been proposed, as I’ll demonstrate below. Furthermore, the debate over whether there are superior metrics appears to be a sideshow to the far more important debate of whether the 2°C limit is too high, reasonable, or too low.

If it is not Victor’s and Kennel’s intent to weaken the 2°C target, they should just say so. They say it is “infeasible,” but the scientific literature says otherwise, as I and others pointed out. Similarly, in a detailed rebuttal, scientists at Climate Analytics explain:

… it is incorrect to claim that achieving this goal is infeasible and cannot be done. The scientific community, in the form of the IPCC AR5 Working Group III report, has assessed that limiting warming below 2°C limit is technically and economically feasible, and at low to modest cost. No one in the scientific community has any doubt about the difficulty of the political decisions that need to made to realise this. Each person is entitled to their own views of whether or not political leaders will take the steps needed, but for the authors to dress up their own judgments — that these decisions will not be made — as a scientific fact is wrong.

Stefan and I pointed out that the Intergovernmental Panel on Climate Change’s Fifth Assessment Report (AR5) says we could stay within 450 ppm of carbon dioxide in the atmosphere at a cost of a mere 0.06 percent in lost growth a year. Victor’s response includes a long discussion about why the economic models are too optimistic, and that “when you start telling the models about the real world the costs go up by a factor of up to three.” Even if true, that would still be barely noticeable against the projected growth rate of some 2.5 percent a year.

And while Victor may again make some handwaving assertions that the cost would be even higher than three times what the IPCC summary says — the fact is that the economic models are notoriously conservative when it comes to accurately figuring out how technological innovation and real world ingenuity drives down the cost of pollution prevention and low carbon technologies.

When you do a technology-based analysis of the 2°C pathway — say, the way the staid International Energy Agency did it this year — you find “an additional USD 44 trillion in investment is needed to secure a clean-energy future by 2050, but this represents only a small portion of global GDP and is offset by over USD 115 trillion in fuel savings.”

And let’s remember that the pure economic models of the cost of action generally ignore the biggest co-benefits. Consider just the health and productivity benefits of just one suite of low carbon solutions, as calculated in the IEA’s latest report “Capturing the Multiple Benefits of Energy Efficiency.” The IEA found that “the uptake of economically viable energy efficiency investments has the potential to boost cumulative economic output through 2035 by USD 18 trillion,” which is larger than the current size of the U.S. economy!

So again, there simply is no basis for Victor or anyone else to dismiss the summary findings of the IPCC. If anything, the IPCC overestimates real world costs, not underestimates them.

So the 2°C target is feasible. But is it scientifically defensible? And is it too high, reasonable or too low?

Again, I agree with Stefan Rahmstorf, Co-Chair of Earth System Analysis at the Potsdam Institute for Climate Impact Research, who said, “If anything, there are good arguments to revise the 2°C limit downward. Such a possible revision is actually foreseen in the Cancun Agreements, because the small island nations and least developed countries have long pushed for 1.5 °C, for good reasons.”

Victor writes of my piece and Rahmstorf’s, “To me it is astonishing that both of these posts seem to take us to task for not being aware of the ‘planetary boundaries’ research (more on that below) when the central conclusion from that work is that real boundaries need to be set in multiple dimensions — exactly what we argue. ”

Actually, it is astonishing to me that Victor cites the planetary boundaries research in his defense, when the central conclusion of that work from a self-described “group of 28 internationally renowned scientists” is that we are already past the planetary boundary for climate!

Let’s dispense with another myth, that somehow there is no scientific basis for the 2°C limit. In fact, even Victor concedes in his NY Times email that early on, “The science was broadly consistent with goals like 2 degrees.” He writes, “we purposely did NOT cite the huge scientific literature that has, ex post, been used to justify 2 degrees because when you look back on that history it isn’t the science that drove this.” But it is tortuous to concede that the 2°C limit was consistent with the science at the time it was proposed and then reject it now without even examining whether the case for 2°C has grown scientifically stronger — and whether that strengthening case is what ultimately led global leaders to adopt 2°C.

Victor and Kennel assert that “this goal — bold and easy to grasp — has been accepted uncritically and has proved influential.” The scientists at Climate Analytics dispute this. “The goal was contested diplomatically for over 13 years and was subject to different levels of scientific and political criticism prior to its adoption at Copenhagen in 2009,” they wrote. “The steady accumulation of evidence, however, in particular from successive IPCC reports, and perhaps most notably from the Nobel prize-winning Fourth Assessment Report (AR4) in 2007, led to the emergence of a political consensus on the 2°C limit.”

Carbon Brief also cites a number of scientists disputing Victor and Kennel. Dr. Joeri Rogelj, a Swiss expert in climate change uncertainty, explains:

“In contrast to what Victor and Kennel suggest, policy makers were very much informed in 2009 and 2010 by the IPCC AR4 on what could be “dangerous” and decided that limiting warming to below 2°C of global temperature increase would be an acceptable level of aggregated risk. Suggesting that policy makers are not aware of the implications of 2°C is being kind of out of sync with the policy reality“.

Okay, the 2°C limit is feasible. And scientifically defensible. And not too low.

So what’s wrong with it? Yes, Victor and Kennel make hand-waving assertions that the so-called “pause” (which occurs mostly in one dataset long known to lowball recent warming) justifies abandoning 2°C. But they “fail to explain why short-term global temperature variability would have any bearing on the 2°C limit,” as Stefan Rahmstorf put it in his debunking post on RealClimate. Victor’s response fails to address or rebut Rahmstorf’s central point here.

And how would other metrics be better? In their Nature piece, the two argue that “the best indicator has been there all along: the concentrations of CO2 and the other greenhouse gases (or the change in radiative forcing caused by those gases).”

That is a head-scratcher. The purpose of the 2°C limit as much as anything else is to tell us roughly what the concentration target is so we can know roughly what the carbon budget is so we can set emissions targets.

Again as the scientists at Climate Analytics explain:

The argument that the 2°C limit cannot be translated into emission goals and budgets is, to put it mildly, unconvincing, and demonstrates a deep ignorance of scientific developments over the last ten years. If this were so, then there would be no science-based policy debate about the size of the gap between where emissions are headed at present and where they need to be in 2020 and 2030 at global, regional, and national levels. In fact, there have been annual scientific assessments of this since 2010.

So the 2°C limit does in fact very much tell us what emission goals and budgets we must abide by. Again, It seems that the Nature piece and Victor’s defense is a not so subtle statement that he wants to weaken the current target. If that is the case, he should just come out and say so and tell us what he thinks is a better concentration target and carbon budget. But if he doesn’t mean to weaken the roughly 450 ppm target then it doesn’t matter how many indicators you have.

As Professor Rogelj told Carbon Brief:

“One of the most important mistakes in the arguments of Victor and Kennel is that they seem to assume that by tracking “vital signs” instead of only pursuing to limit warming to below 2°C, the world would have more time to act and climate action would be less stringent. This is wrong.”

And the link provided is to the 2013 Nature article, titled, “Allowable carbon emissions lowered by multiple climate targets.”

Ironically, in Nature, Victor and Kennel argue that “policy-makers should also track ocean heat content” because it “is a good proxy for the long-term risk to future generations and planetary-scale ecology.” Well, the new ocean heat content study we reported on makes clear two things. First, tracking ocean heat content is considerably harder than tracking surface air temperature. And the world is warming faster than we thought.

So as Professor Pierre Friedlingstein told Carbon Brief, “We can replace that [2C] target by any combination of atmospheric CO2, ocean heat, sea-ice, etc, it will not change the main message: There isn’t much time left for inaction.”

Precisely. Unless of course more time for inaction is what Victor and Kennel want. But if it is, they should just say so. If it isn’t, then surface temperature is a perfectly fine metric, and 2°C a perfectly reasonable (though possibly too high) limit.

One final comment. Rahmstorf has updated his RealClimate piece to respond to Victor this way:

I was most surprised by the fact that he says that I use “the same tactics that are often decried of the far right — of slamming people personally with codewords like “political scientist” and “retired astrophysicist” to dismiss us as irrelevant”. I did not know either author, so I looked up Thomson Reuters Web of Science (as I routinely do) to see what their field of scientific work is. I have no idea why calling someone a political scientist or astrophysicist are “codewords” (for what?) or could be taken as “ad hominem slam” (I’m proud to have started my career in astrophysics), or why a political scientist should not be exactly the kind of person qualified to comment on the climate policy negotiation process. I thought that this is just the kind of thing political scientists analyse. In any case I want to make very clear that characterising these scientists by naming their fields of scientific work was not intended to call into question their expertise, nor did my final paragraph intend to imply they are trying to sabotage an agreement in Paris — I just fear that this would be the (surely unintended) effect if their proposal were to be adopted.

Let me agree with Rahmstorf, and add that I am baffled that “political scientist” and “retired astrophysicist” are code words for irrelevant. I saw Rahmstorf used them, so I looked them up, since they seemed accurate, I used them. So much for this code word conspiracy.

It is particularly bizarre that Andy Revkin of DotEarth would assert those accurate descriptions are “not-so-subtle efforts” to show Victor and Kennel are “not legitimate voices on such an issue.” DotEarth rarely if ever describes me in terms of my training as a physicist or my relevant experience as former acting assistant secretary of energy for energy efficiency and renewable energy. Instead, I am typically labeled a “climate campaigner” or something dismissive like that. I would be delighted to be as accurately described on DotEarth as Victor and Kennel were on ClimateProgress. Hopefully going forward, I will be.