This is very bad. Via The New York Times: Extreme Weather and Drought Are Here to Stay. Click through for the full report and several links. And for the abstract of the original scientific report, click through to Nature Geoscience. Excerpt:
In terms of severity and geographic extent, the 2000-4 drought in the West exceeded such legendary events as the Dust Bowl of the 1930s. While that drought saw intervening years of normal rainfall, the years of the turn-of-the-century drought were consecutive.
More seriously still, long-term climate records from tree-ring chronologies show that this drought was the most severe event of its kind in the western United States in the past 800 years. Though there have been many extreme droughts over the last 1,200 years, only three other events have been of similar magnitude, all during periods of “megadroughts.”
Most frightening is that this extreme event could become the new normal: climate models point to a warmer planet, largely because of greenhouse gas emissions. Planetary warming, in turn, is expected to create drier conditions across western North America, because of the way global-wind and atmospheric-pressure patterns shift in response.
Indeed, scientists see signs of the relationship between warming and drought in western North America by analyzing trends over the last 100 years; evidence suggests that the more frequent drought and low precipitation events observed for the West during the 20th century are associated with increasing temperatures across the Northern Hemisphere.
These climate-model projections suggest that what we consider today to be an episode of severe drought might even be classified as a period of abnormal wetness by the end of the century and that a coming megadrought — a prolonged, multidecade period of significantly below-average precipitation — is possible and likely in the American West.
The current drought plaguing the country is worryingly consistent with these expectations. Although we do not attribute any single event to global warming, the severity of both the turn-of-the-century drought and the current one is consistent with simulations accounting for warming from increased greenhouse gases.
The Northern Hemisphere has just recorded its 327th consecutive month in which the temperature exceeded the 20th-century average. This year had the fourth-warmest winter on record, with record-shattering high temperatures in March. And 2012 has already seen huge wildfires in Colorado and other Western states. More than 3,200 heat records were broken in June alone.
And yet that may be only the beginning, a fact that should force us to confront the likelihood of new and painful challenges.
A megadrought would present a major risk to water resources in the American West, which are distributed through a complex series of local, state and regional water-sharing agreements and laws.
Virtually every drop of water flowing in the American West is legally claimed, sometimes by several users, and the demand is expected to increase as the population grows.