My last post criticized changes made to the recent IPCC report by Richard Tol after the last round of external reviews. There’s a lot of material involved, and I won’t go into it here. Instead, I’d like to show how I was an idiot in my previous discussions of this topic.
Here is a graph from Richard Tol’s 2009 paper. Pay attention to what I highlighted in its caption:
Compare that to the graph shown in the IPCC report:
Notice this caption does not say what starting temperature was used. The text of the section its in doesn’t either:
Since AR4, four new estimates of the global aggregate impact on human welfare of moderate climate change were published (Bosello et al., 2012; Maddison and Rehdanz, 2011; Roson and van der Mensbrugghe, 2012), including two estimates for warming greater than 3°C. Estimates agree on the size of the impact (small relative to economic growth) but disagree on the sign (Figure 10-1). Climate change may be beneficial for moderate climate change but turn negative for greater warming. Impacts worsen for larger warming, and estimates diverge. The new estimates have slightly widened the uncertainty about the economic impacts of climate.
A reader could assume the IPCC figure referred to temperature changes from today, but that is only an assumption. Only someone who had read other work, like Tol’s 2009 paper, would know this analysis is for what we can expect in the future. And by “know,” I mean, “would be tricked into believing.” Here’s the updated version of that graph and its caption (from here:
Pay close attention to its caption. It says:
estimates of the global economic impact of climate change, expressed as the welfare-equivalent income gain or loss, as a function of the increase in the annual global mean surface air temperature relative to preindustrial times.
“[R]elative to preindustrial times” is quite different than “relative to today.” There’s been ~.85C warming since preindustrial times (see page three). That means the x-axis in his original graph was off by nearly one full degree.
That’s a significant error. The only portion of Tol’s graph which shows increasing values is the first ~1C. If you cut off the first .85 of it, there’s practically no increase. This is what would have fit Tol’s caption:
Nobody seeing that graph would think global warming is a good thing. Maybe global warming was a good thing in the past, but that graph says it will only make things worse in the future.
Of course, Tol didn’t tell people that. He published a paper saying global warming will be beneficial for the next two degrees of warming. He told the media we’d see such benefits. Everybody understood his work as saying future warming would be a good thing. Here are a couple explicit examples:
As Tol’s diagram quite clearly indicates, the consensus of economic studies finds that global warming would be on net beneficial to human welfare, at least through 2C degrees of warming (and this is relative to the current baseline, not to preindustrial times).
At first, I thought this was just their usual bluster. But then I realised that they are genuinely unaware. Good news is no news, which is why the mainstream media largely ignores all studies showing net benefits of climate change. And academics have not exactly been keen to push such analysis forward. So here follows, for possibly the first time in history, an entire article in the national press on the net benefits of climate change.
To be precise, Prof Tol calculated that climate change would be beneficial up to 2.2˚C of warming from 2009 (when he wrote his paper). This means approximately 3˚C from pre-industrial levels, since about 0.8˚C of warming has happened in the last 150 years. The latest estimates of climate sensitivity suggest that such temperatures may not be reached till the end of the century — if at all. The Intergovernmental Panel on Climate Change, whose reports define the consensis, is sticking to older assumptions, however, which would mean net benefits till about 2080. Either way, it’s a long way off.
Even Richard Tol’s critics generally failed to notice this problem. The blogger Anders wrote about this conclusion, taking for granted:
What I was interested in is if there was any evidence that there could be a net benefit from 2 degrees of warming (relative to pre-industrial levels). In a comment on a recent post, Martin linked to a 2008 paper (actually an ESRI working paper) by Richard Tol called The Economic Impact of Climate Change. The paper is really a review of 13 studies (and 14 estimates) that have considered the economic impacts of climate change. The basic result is shown in the figure below. It shows the percentage change in GDP for increases in global surface temperature (relative to today) of up to 3oC. There is a suggestion that a rise of 1oC (i.e., almost 2oC relative to pre-industrial times) could be beneficial, but anything beyond 2oC (relative to today) seems likely to be detrimental.
A few people did notice the issue, but only after Tol was forced to publish a correction. For four years, everybody was deceived by Richard Tol into believing his work estimated global warming will cause net benefits for a significant amount of time. In reality, his work estimates global warming will pretty much only cause harm from now on.
At least, that’s true if we believe what Richard Tol says about his work now. Mabye we shouldn’t. My brief perusal of the sources he used shows at least some of the estimates are for changes since pre-industrial times. I don’t know that they all are though. It’s possible some may have used modern times as a starting point. If so, Tol’s work is pointless as some unknown number of estimates he used are wrong.
Regardless, it makes the new text of the IPCC report rather interesting. How can it say:
Estimates agree on the size of the impact (small relative to economic
growth) but disagree on the sign (Figure 10-1).
When we now know the only meaningful positive estimate is (basically) for where we are now, not where we’ll be in the future? How can it say:
Climate change may be beneficial for moderate climate change but turn negative for greater warming.
When every version of Tol’s own work apparently says we can only expect things to go down hill?
And beyond all this, if Tol’s correction is right, and those estimates really are relative to pre-industrial, not modern times, why did Richard Tol say otherwise for four years? Why is it when he finally corrected himself, he didn’t even attempt to draw attention to this correction? Why didn’t he do anything to let people who have been relying upon his work know that work was wrong?
And what’s the point of having peer-review, much less having thousands of scientists review the IPCC reports, if they can’t catch such a fundamental, and simple, problem?