By Greg Ip
This week Scott Pruitt, head of the Environmental Protection Agency acknowledged that humans do indeed contribute to a warming climate.
Mr. Pruitt’s concession to scientific consensus came with a caveat: “The real issue is how much we contribute to it and measuring that with precision.” Indeed, how regulators measure climate impact matters more than agreeing that such an impact exists. This makes President Donald Trump’s order last week scrapping official estimates of the “social cost of carbon” especially significant. Without actually disputing the science behind climate change, it drastically raises the bar to acting on it.
Federal rules are supposed to cost the economy and society less than the harm they prevent. But regulators long lacked any benchmark for the costs of greenhouse gas emissions. Courts have ruled they can’t assume the costs are zero, so in 2010 Barack Obama’s administration, after lengthy study, began estimating the social cost of carbon. It put the future damage, such as from rising sea levels, crop damage and heat-related death, of emitting one metric ton of carbon dioxide in 2015 at $42…
…But the answer to imperfect models isn’t to ignore them but to improve them. Michael Greenstone, a University of Chicago economist who led the Obama administration’s effort, says about 150 reputable studies of climate damage have been released since 2009 and they would appear to justify an even higher social cost of carbon: “The evidence so far is that the damages are greater than we understood” for example due to heat-related deaths in India.
And uncertainty alone doesn’t justify inaction. Military and terrorist attacks are also highly uncertain, yet the U.S. spends more than 3% of national income to prevent them on the theory that spending nothing makes an attack more likely. Moreover, their consequences are asymmetric: peace in the best case scenario, nuclear annihilation in the worst…
Continue reading at The Wall Street Journal…