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Big Report: How Climate Change Affects The United States

Earlier this afternoon, the White House held a press conference to talk up a major new NOAA report on likely climate-change impacts in the United States. I don't know if this is a first step in a concerted new push by the Obama administration to build support for action on global warming (the White House has stayed remarkably quiet on this issue so far), but the report vividly illustrates why the country can't just ignore climate change. Impacts are already occuring, right in our backyard, and it's only getting worse.

Among the major findings: If the world continues on a business-as-usual path, allowing emissions to grow at their current pace, then the mainland United States is likely to warm an additional 7F to 11.5F by 2090. (There's some uncertainty around the exact figure.) In the worst case, that's a 1F increase each decade from now until the end of the century.

One particularly eyebrow-raising slide from the presentation, I thought, looked at the number of days each year in which the local temperature will rise above 90F. Here in Washington, D.C., we already have heinously hot summers, but there are only about 30 to 40 days each year that are actually hotter than 90F. But by 2080, if emissions keep rising as usual, we'll be seeing hotter-than-90F days some 90 to 100 days each year. Those miserable D.C. Augusts will essentially extend for one-quarter of the calendar year:

If that sounds ugly, consider that parts of the Southwest, South Florida, and South Texas could see more than 180 days (!) per year with temperatures over 90F. And it's not just that this will be extremely unpleasant: More hot days could also mean more heat-related deaths, especially as the U.S. population ages. During the press conference, Tom Karl, director of the National Climatic Data Center, told reporters that current projections have heat-wave deaths in Chicago, for example, rising tenfold by century's end, although there are ways to adapt to this (planting more shade trees in the city; installing green roofs).

A few other notables: As the country heats up, there are likely to be longer dry periods coupled with more intense downpours. The North will get wetter, the South drier, although it's not exactly clear where the demarcation line lies. There's going to be a lot of stress on water resources out West. Also, if sea levels rise 3 to 4 feet by century's end, then a good chunk of Florida will find itself underwater, including the Florida Keys, Everglades National Park, much of Cape Canaveral, and the Barrier Islands. Basically, the red areas on this map:


The Gulf Coast is another place to fret about sea-level rise, as some 2,400 miles of major roadway and 246 miles of freight are at risk of permanent flooding in the next 50 or so years--terrible news for such a vital port area. (Six of the country's top ten freight gateways and seven of its ten large ports could face major disruptions.)

Anyway, the full NOAA report is here, including sub-reports grouped by region, so you can see how climate change could affect your specific area. The broader study dispels the notion that climate change will only impact poorer countries. As Karl put it at the press conference, a changing climate will have positive and negative effects in the United States. "But overall, most of the impacts will be negative. This is because we've designed and built our infrastructure for the climate we already have, not the climate we're going to have." What's more, even if we do curb emissions drastically and avoid the most severe temperature increases, some amount of warming is already underway, which means that adaptive measures will prove necessary no matter what.

--Bradford Plumer