woman in desert, feeling the heat
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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 Epidemiology 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.

2. Extreme drought and rainfall. Overall, warmer temperatures will mean more evaporation and more water shortages. This will be especially true in the already-dry Southwest, where they are currently experiencing an intense, multi-year drought. Droughts can unleash a cascade of other effects. “Drought conditions may increase the environmental exposure to a broad set of health hazards including wildfires, dust storms, extreme heat events, flash flooding, degraded water quality, and reduced water quantity,” reports the NCA. But more evaporation can also lead to more intense rainfalls, leading to flooding, property damage, drowning, and deaths from other causes, such as people being cut off from emergency medical services. “The hospital where I was born in Binghamton, N.Y., was flooded in 2006, and they had to evacuate it,” notes Knowlton. Shutting down a hospital “really has effects on people’s health.” A heavy storm can also overwhelm a city’s sewage treatment facilities, forcing it to dump untreated water into the nearest river. That, in turn, increases everyone’s exposure to waterborne bacterial diseases like diarrhea. This doesn’t just mean more hilarious movie scenes. “A Minneapolis hospital showed an increasing outbreak [of diarrhea] among children after extreme precipitation events,” says Perera. It sucks enough to be hospitalized as a kid, but then imagine getting hit with a miserable, potentially deadly stomach bug on top.

3. Agriculture and food security. Paying more for your margarita because of the lime shortage will be the least of your problems. Increasing extreme weather and more unpredictable precipitation are terrible for farmers. “Many crop yields are predicted to decline due to the combined effects of changes in rainfall, severe weather events, and increasing competition from weeds and pests on crop plants,” reports the NCA. “Livestock and fish production is also projected to decline. … Americans with particular dietary patterns, such as Alaska Natives, will confront shortages of key foods.” As food production declines, food prices will rise — and so will food insecurity. “In such situations, people cope by turning to nutrient-poor but calorie-rich foods, and/or they endure hunger, with consequences ranging from micronutrient malnutrition to obesity.” Even some foods themselves will become less healthful: “Elevated atmospheric CO2 is associated with decreased plant nitrogen concentration, and therefore decreased protein, in many crops, such as barley, sorghum, and soy.”

4. Insects. Diarrhea-causing microscopic bacteria aren’t the only pests we’ll have to worry about. Warmer weather will expand the geographic range of disease-carrying bugs such as ticks and mosquitos. And insects from warmer climes can bring some bad guests, as can be attested by everyone who participates in New York City’s new annual tradition of freaking out about the West Nile Virus. Lyme disease will be found in a larger area. Non-insect-borne diseases may spread as well. Valley fever, caused by a deadly fungus normally found in California and Arizona, has recently been discovered as far north as Washington state. Researchers at Washington State University say it may have been spread northward by warmer temperatures.

5. Air pollution. There are several ways that climate change will cause an increase in air pollution. The first is the formation of ozone, which is the main ingredient in smog. It is created by sunlight and heat interacting with pollutants, and warmer summers are already causing spikes in ozone, according to the American Lung Association. Droughts lead to more dust that is dangerous to breathe, and wildfires spew ash into the air. Warmer and wetter weather will wreak havoc on allergy and asthma sufferers, as it leads to longer and more severe seasons for ragweed and pollen.

The Obama administration hopes that if the American people understand these tangible, regional consequences of climate change — and others, such as the devastating effects on rural communities — they will support action to reduce greenhouse gas emissions. “[The NCA] breaks the United States down into eight regions, in contrast to the IPCC, which treats all of North America as one region,” noted Jerry Melillo, who chaired the National Climate Assessment and Development Advisory Committee, on Tuesday’s conference call.

If anything can motivate Americans to care about climate change, it will be negative effects they can see right at home. But will even that be enough?