As the UN hosts its annual meeting on climate change this week, it is imperative that we continue to place an emphasis on the strongest evidence to inform how our society should respond. Last month, coincidentally timed with the Thanksgiving holiday, the U.S. government released one such summary of evidence – its latest National Climate Assessment. This sweeping report summarized the work of thousands of top researchers and pointed towards one overwhelming conclusion: climate change is occurring, predominantly driven by human activities, and harming people in ways we can see today that will only get worse without further action. One number you probably saw grabbing headlines is that warming could clobber the nation’s economy by 10%. That number did not appear in text of the report. It was instead interpreted from a chart in the final chapter. The way it resonated shows how eager people are for this kind of risk-based economic assessment.
But the statistic mischaracterizes the evidence. How do I know? I, working with a team of climate scientists, economists, and computer scientists, produced that evidence. It originated in a peer-reviewed analysis that was published in Science magazine last year.
Let’s unpack this “10%” a bit. The original statement warned that climate change could “knock as much as 10 percent off the size of America’s economy by century’s end.” It only takes a quick glance at the figure from which that number is drawn for even the most stubborn observer to see that we emphatically did not only look at extreme scenarios.