It’s 30 years since James Hansen testified before the US Congress about climate change. In the same year, he published a paper that produced some forecasts. I wasn’t going to write about this as there are a number of articles discussing what Hansen presented and highlighting how it’s stood up remarkably well. There’s Eric Holthaus in Grist, Gavin Schmidt at Realclimate, Zeke Hausfather at Carbon Brief, and Tamino at Open Mind.
Patrick Michaels and Ryan Maue have also written an article looking at how Hansen’s global warming predictions have stood up. They conclude that they haven’t stood up very well. Drawing this conclusions, however, requires making some rather odd claims. For example
Well, if you leave out some data you can draw all sorts of conclusions. However, why was the 2015/2016 El Niño warmer than the 1997/1998 El Niño? Why are La Niñ’a’s today warmer than El Niño’s of the past? It’s because there’s an underlying warming trend and, as the figure on the right shows, there is little indication that the rate of warming has slowed.
Global surface temperature has not increased significantly since 2000, discounting the larger-than-usual El Niño of 2015-16.
In Hansen’s paper, he selected 3 different emissions scenarios, one in which emissions continued to increase (A), one in which the rate stayed similar to what it was in the 1980s (B), and one in which they basically stop in 2000 (C). The Michaels and Maue article implies that temperatures have followed the latter scenario, while emissions have continued to rise. However, not only is this claim about temperatures wrong, what’s more relevant is the change in forcing, what turns out to have been between scenario B (constant rate of emission) and C (emissions stop in 2000). The resulting temperature change turns out to, therefore, be quite similar to what has been observed (see here).
The article finishes with
On the 30th anniversary of Mr. Hansen’s galvanizing testimony, it’s time to acknowledge that the rapid warming he predicted isn’t happening. Climate researchers and policy makers should adopt the more modest forecasts that are consistent with observed temperatures.
That would be a lukewarm policy, consistent with a lukewarming planet.
Firstly, it is not true that forecasts are not consistent with observations (see here). Secondly, what is lukewarm policy? Seems to me that if you accept that climate sensitivity lies somewhere within the standard likely range, think we should limit warming to something reasonable (say, below 4K), and think we should do so without shocking the global economy, then it’s not clear to me that there is much difference to the basics of what you would want policy to achieve. We would need to aim to get emissions to ~zero by the second half of this century. We could quibble about the details, but the basic goal would seem to not depend strongly on where you think climate sensitivity actually lies.
Both Michaels and Maue are associated with the Cato Institute, which seems to essentially be the US version of the UK’s Global Warming Policy Foundation, so I probably shouldn’t be surprised that they can write such a nonsensical article.
James Hansen’s legacy: Scientists reflect on climate change in 1988, 2018, and 2048 (Eric Holthaus in Grist).
30 years after Hansen’s testimony (Gavin Schmidt at Realclimate).
Analysis: How well have climate models projected global warming (Zeke Hausfather at Carbon Brief).
Global warming: Told you so (Tamino).
Update check on Hansen’s 1988 projections (Nick Stokes at Moyhu).