Most significantly, the National Climate Assessment—which is endorsed by nasa, noaa, the Department of Defense, and 10 other federal scientific agencies—contradicts nearly every position taken on the issue by President Donald Trump. Where the president has insisted that fighting global warming will harm the economy, the report responds: Climate change, if left unchecked, could eventually cost the economy hundreds of billions of dollars per year, and kill thousands of Americans to boot. Where the president has said that the climate will “probably” “change back,” the report replies: Many consequences of climate change will last for millennia, and some (such as the extinction of plant and animal species) will be permanent.
The report is a huge achievement for American science. It represents cumulative decades of work from more than 300 authors. Since 2015, scientists from across the U.S. government, state universities, and businesses have read thousands of studies, summarizing and collating them into this document. By law, a National Climate Assessment like this must be published every four years.