Climate change threat to US crops and water

• Ed Pilkington in New York
• The Guardian,
• Thursday May 29 2008

The US south-west, a region that is experiencing one of the fastest rates of population growth, faces dramatic challenges in the next 50 years from drought, wild fires and changing ecosystems caused by global warming, a report from the Bush administration warns.

The paper, commissioned by the US department of agriculture, looks at the likely impact of rising temperatures caused by higher emissions of CO2 during the next 25 to 50 years on America's agriculture, land and water resources and biodiversity. It warns that the country will be affected in strikingly different ways, with most of the negative impacts falling on the south-western and western US.

Climate change, it says, has already led to visible shifts. Much of the east and south of the country now receives more rainfall than a century ago, while the south-west has less. That process, and the changes in plant and animal life that follow, are likely to increase as temperatures rise by 1-4C, the report says. Among the most alarming threats will be an increase in wildfires and a spread of invasive grasses and other weeds that will be difficult to control with current pesticides.

The report is based on a survey of existing scientific research and forms part of a series of investigations into climate change ordered by President George Bush in 2003.

Its message is particularly worrisome for a region that happens to have some of the highest population growth rates in the US. Some 50 million people live in the south-west and towns such as Las Vegas and Phoenix are expanding rapidly with an influx of retiring baby-boomers attracted by the relatively cheap cost of land and the warm winters.

Water levels are already falling in some parts through rising demand, and according to the report, that pressure can only increase, as it predicts that by 2060 rainfall will be down by a fifth. As temperatures rise, growing seasons will extend, but the $200bn farming sector will have to contend with more severe summer droughts, widening arid areas, and the spread of weeds. Diseases that strike both crops and farm animals will extend their reach.

The scientists who produced the report warn: "Many plants and animals in arid ecosystems are near their physiological limits for tolerating temperature and water stress, and even slight changes in stress will have significant consequences."