The Downside of Research: How Small Uncertainties Can Lead to Big Differences

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Most research yield very few conclusions with 100 percent certainty — that’s why you’ll often hear economists state their conclusions with “95 percent certainty.” It means they’re pretty sure, but there’s still a small margin of error. The science of climate change is no different, and, according to a Washington Post blog post, scientists are struggling with how to explain that uncertainty to the public. “What do you do when there’s a small but real chance that global warming could lead to a catastrophe?” asks Brad Plumer. “How do you talk about that in a way that’s useful to policymakers?”

Plumer goes on to provide an example:

The Intergovernmental Panel on Climate Change’s 2007 report had a section on future sea-level rise. At the time, there was still debate over how quickly ice caps in Greenland and Antarctica would melt as the poles warmed. (Roughly speaking, it was unclear whether the melting ice sheets would largely stay in place and drip water into the oceans or whether big chunks would slide off into the sea.) So the IPCC models explicitly left out estimates of “future rapid dynamical changes in ice flow” and forecast that sea levels would rise just 18 to 59 centimeters by 2100, largely caused by thermal expansion of the oceans.

In a sense, this was “accurate,” representing what the broad scientific community could say with high levels of confidence. The report even added a caveat: “Larger rises cannot be excluded, but understanding of these effects is too limited to assess their likelihood.” In another sense, though, the IPCC was acting too conservatively, giving an overly rosy picture of the rising oceans. In the years since the 2007 report, researchers have learned more about the dynamics of ice sheets and are converging on the view that we’re facing at least a one-meter rise by century’s end if emissions aren’t tamed.

In an effort to address the problem, scientists Michael Oppenheimer and Gary Yohe have edited a special issue of Climactic Change dedicated to the topic. “If we had all the time in the world to study this, it would be no big deal, it’d just be some arcane scientific debate,” says Oppenheimer. “But because there’s a policy context, there’s an added urgency in getting it right.”