The lush vines of California are among the most iconic images of America, with the perfect climate between the baked Central Valley and the cool Pacific coast enabling the area take its place as one of the great success stories of the boom in new-world wines.

The industry is worth billions of dollars a year and has starred in its own movie, the wine-buff-midlife-crisis road-trip hit Sideways. But just as American wines from the now famous Napa and Sonoma valleys and other enclaves have established their place at the world's top tables, a new report has warned that global warming may destroy the industry.

The study forecasts that by the end of this century up to four-fifths of the best vine-growing areas will no longer be able to grow their premium grapes because of the steady rise in very hot days, when temperatures pass 35C. And with California now in a state of emergency because of a two-week heatwave in which temperatures have soared to 49C, and which has been blamed for killing more than 120 people, the wine industry faces an imminent crisis, says Dr. Noah Diffenbaugh, one of the study's authors. Such a dramatic change would affect wine drinkers around the world.

"The climate change we're predicting for the late 21st century is so far above those maximum tolerances [to very hot days], we'd expect to see those changes a lot sooner," said Diffenbaugh, of Purdue University in Indiana.

Until now global warming studies have been limited to general statements about the likely rise in the Earth's average temperatures caused by the build-up of greenhouse gases in the atmosphere. These studies predicted that warming would be a boon for the wine industry.

The latest report on California's wines is part of a new trend for much more detailed studies of how warming will affect local climates. In Europe vines are already being planted as far north as York, in the far north of England, and could start thriving in different areas of France and other major producing countries, where harvests are also starting earlier. And researchers in Britain have predicted the landscape will be transformed by widespread planting of other warmer crops, such as sunflowers, sweetcorn and elephant grass. Some scientists are uneasy about such far-distant and local forecasts, however.

"What they are doing is taking relatively coarse [global] assumptions and adding what appears to be realistic [local] detail, more complexity, but it doesn't guarantee it's going to be right or any better," said Kevin Trenberth, of the U.S. National Centre for Atmospheric Research, one of the authors of a report due out next year from the UN's International Panel on Climate Change.

© Guardian Newspapers Limited 2006

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