In this new series we’re surveying past estimates of Equilibrium Climate Sensitivity (the crucial absolute amount of warming to be expected from any relative doubling of atmospheric CO2 – see Backgrounder here) based on observations rather than computer models. These days the latter say ECS is between 1.8C and 5.6C. And the range matters, a lot, because economists say that if it’s about 2C or under then global warming is not a problem and climate policy of any meaningful sort is not worth the cost. So what does the climate itself say? Back in 2012 a group of climatologists led by Michael Ring of the University of Illinois crunched the historical numbers and concluded that, if you use the NASA temperature data ECS is about 1.5C, if you use the NOAA data it’s about 2.0C and if you use the HadCRUT data from the Climate Research Unit it’s about 1.6C. But you might be surprised what the authors thought this modest range of numbers proves.
The article opens by lamenting the sorry state of understanding of the unwashed plebes, otherwise known as the US public. Only about half, according to surveys in 2010 and 2011, believe that “pollution from human activities” is responsible for most climate change, and this translates into political resistance to major emission reduction policies. So, the authors decided to write a super-simple article that anyone in the public could understand to prove that greenhouse gases really are to blame.
We don’t much like the idea of scientists writing articles with the intent of pushing a political agenda. But in this case there wasn’t any danger that the public would rush to read it because their “simple” approach involved developing two mathematical models, one a climate forcing equation estimated based on the minimized root mean squared error, and the other a Singular Spectrum Analysis using quasi-periodic oscillations. Got that? Way to reach out to the rubes.
Whatever the fancy jargon means, other than that university science faculties could usefully add a course on clear communication, when the data were plugged in and the results popped out the authors noted with great satisfaction that greenhouse gases are responsible for most of the warming, at least in the last few decades. Even though, they admitted with some puzzled chin-stroking, ECS is awfully low compared to the IPCC range of 1.5C to 4.5C. And they had to admit that warming in the period before 1944 and cooling from 1945 to 1976 was mainly natural. Greenhouse gases only took over from 1977 to 2010. So it’s not exactly a stinging rebuttal to the dunces off campus.
Especially when it adds yet more evidence that ECS is 2C or less. Despite which the authors came out thinking exactly what they thought going in, namely full steam ahead for climate policy:
“Climate scientists of course know that the large imbalance between current CO2 emissions and natural removal processes, and the long resident lifetime of CO2 in the atmosphere, render the “wait-and-see” approach impossible and dangerous. Mitigation of human-caused climate change requires immediate corrective action... We hope this study contributes to a public realization that emissions reductions are necessary to safeguard Earth’s climate.”
Well of course you do. Never mind what your research actually found.
Again, to reiterate, we don’t think very highly of scientists writing reports to push a political or even a policy agenda. Give us the numbers and let the public decide based on the costs as well as the benefits of the policy proposal. And in this case, contrary to the authors’ claims, a 1.6C value for ECS is not dangerous, and implies the wait-and-see approach is the right one.