Each ton of carbon pollution from cars, planes, and power plants comes with costs. It harms our environment and threatens our health, it drives climate change, and it negatively impacts our economy. The White House has attempted to develop a standard estimate of these costs, called the “social cost of carbon,” for agencies to use in analyzing the benefits of rules designed to reduce carbon emissions. In an Aug. 25 report, the Government Accountability Office (GAO) validated that effort.