An Important Report on Climate and Extreme Events

The IPCC has issued a special report on “Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation” (SREX). It’s an immensely useful document. Those of us whose research focuses on policy responses to climate change are bombarded daily with new studies that claim to have established that this or that cataclysmic outcome (devastating drought, mass species extinction, hurricanes galore) is a virtual certainty. But I’ve picked through too much bad climate-related work, including in top journals like Science and Nature, to simply accept every peer reviewed paper on faith. Indeed while these studies are often compelling, it’s difficult to separate those that are genuinely solid from ones that rest on less stable ground. That’s why institutions like the IPCC, and reports like this new one, are so valuable.

I take three big messages from from the study. The first is that there are a host of extreme events – particularly much larger numbers of unusually hot days and heat waves – that are virtually guaranteed given current emissions trends. The second is that there are a bunch of other worries – including, most prominently in the report, more intense cyclones – that are quite likely to materialize. The third, though, is that for many of the risks that people often talk about, ranging from greater drought to increased odds of big floods, there remains enormous disagreement that isn’t reflected by some of the more breathless reports about recent scientific work. I don’t want to suggest that this is reason for avoiding action on climate change – fifty-fifty odds of widespread drought is plenty bad for me. Nonetheless, the nuanced parsing of the literature is helpful.

I’d be remiss if I didn’t flag a handful of problems with the study, in part because I think there are some lessons to be learned for future IPCC reports. The SREX exercise was aimed at assisting with adaptation planning. It thus models a wide range of emissions scenarios, one of which is far more benign than anything one might expect given current policy. As a result, some of the conclusions in the report are muddied, since it’s sometimes impossible to tell whether a particular outcome is uncertain because of limited climate knowledge or because the outcome will depend on the emissions path. In many cases, the report elaborates on distinctions between the emissions cases, but it does not do that consistently enough.

The study executive summary is also being released several months before the actual study, which won’t be out until February. Flaws in past IPCC summaries have typically been brushed aside with allusions to the more sophisticated full reports. But the IPCC knows that it’s the first release – in this case the executive summary – that will get all the attention. They should have waited until they could release the whole thing before they went public. Relatedly, the study seems to have been rushed into print so quickly that figure and table captions are in different parts of the document from the figures and tables themselves. That’s a fine format for journal subsmissions, but it makes the study absurdly difficult to read. Some of the travails of the IPCC over the past few years have clearly taught its leaders lessons about how to approach uncertainty, particularly in its summary documents. But they still have some way to go in polishing the operation.