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On Tuesday, the Obama administration released the third National Climate Assessment, laying out in detail what global warming means for the country. This NCA is the longest – over 800 pages – and most comprehensive yet.

“Climate change is not a distant threat; it’s already affecting the U.S.,” said John Holdren, director of the White House Office of Science and Technology Policy, in a conference call with reporters about the report. “This is the largest alarm bell to date.”

There is a lot in the report to contemplate, but here’s a central takeaway: Climate change is deadly, and Americans have already begun to die from it. How many more will die depends on how much more CO2 we belch into the atmosphere.

There are five main ways in which climate disruptions can lead to injury, illness, and death:

1. Extreme heat. “Heat kills people, and it sends thousands of people to emergency rooms because climate change fuels longer and more severe heat waves,” says Kim Knowlton, a scientist with NRDC’s health and environment program and an author of the Human Health chapter of the NCA. “There will be 10 more days over 100 degrees for the entire country on average from 2021 to 2050,” notes Liz Perera, a federal climate policy analyst at the Sierra Club. “The interesting thing there is that regionally there’s actually quite a distribution difference. It will be worst in the Southwest, Southeast, and Great Plains.” Those, of course, are already the places with the harshest summers. The U.S. has recently seen its worst heat waves in history, and increasing casualties as a result. A study published in the journal
Epidemiologyn found, for example, that in July 2006, “California experienced a heat wave of unprecedented magnitude and geographic extent   Coroners attributed 140 deaths to hyperthermia, and it has been estimated from vital statistics data that in excess of 600 heat-related deaths may have occurred over a 17-day period.” The study also found that climate change is causing worse humidity to accompany heat waves, making them more unpleasant and dangerous.