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. 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.