Western US Drying

Researchers have found that areas in the western US, including places like Las Vegas, Los Angeles, and San Diego, are drying due to human activity. From NatureNews:

Human activity is largely to blame for the worsening water shortages in the western United States over the past half-century, a new study shows. The analysis of climate trends that influence the availability of freshwater shows that humans are responsible for 60% of the observed changes. ...

Snowpack in mountain ranges such as the Rockies is diminishing, average minimum temperatures are rising, and spring run-off in major rivers such as the Colorado river is happening earlier. All of these changes look set to make dry summers even harsher for residents of thirsty cities such as Las Vegas in Nevada, and Los Angeles and San Diego in California.

Research led by Tim Barnett of the Scripps Institution of Oceanography in La Jolla, California, now shows that these changes cannot be explained without taking human activities — which have raised greenhouse-gas levels — into account. Barnett is so worried by the situation that he says development in these regions should be capped. "We're using all the water there is right now, and people still want to build bigger cities," he says. ...

Barnett and his team used computer models to simulate the natural behaviour of the water cycle in the region. They compared this to the trends seen over the past 50 years, to see whether they can be attributed to natural causes. The answer, they report in this week's Science, is no.

Barnett and his colleagues then factored in the global warming that has occurred as a result of burning fossil fuels over the past half-century, using figures calculated by the Intergovernmental Panel on Climate Change (IPCC). This time, the models matched more closely the weather trends experienced in the western US states.

Overall, says Barnett, human greenhouse emissions explain around 60% of the trends in freshwater behaviour. He puts the odds of natural causes being responsible at "somewhere between 1 in 100 and 1 in 1,000".