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Tuesday, July 11, 2006 - Page updated at 07:57 AM


West Coast climate change could threaten wine production, study suggests

WASHINGTON — Climate warming could spell disaster for much of the multibillion-dollar U.S. wine industry.

Areas suitable for growing premium wine grapes could be reduced by 50 percent — and possibly as much as 81 percent — by the end of this century, according to a study Monday in Proceedings of the National Academy of Sciences.

The paper indicates increasing weather problems for grapes in such areas as California's Napa and Sonoma valleys.

The main problem: an increase in the frequency of extremely hot days, said Noah Diffenbaugh of the Department of Earth and Atmospheric Sciences at Purdue University.

Grapes used in premium wines need a consistent climate. When temperatures top about 95 degrees, the vines have problems maintaining photosynthesis and the sugars in the grapes can break down, said Diffenbaugh, a co-author of the report.

Until now, climate studies centered only on the impact of average temperature increases on wine production and concluded that wine growers might, if anything, benefit from the temperature increases expected in coming decades.

The new study, funded by the National Science Foundation, the National Aeronautics and Space Administration and Purdue University, involved five months of supercomputer calculations. It is the first study in which researchers have been able to calculate the daily temperature swings from various climate-change scenarios in such detail.

For the purposes of their computer simulation, the researchers assumed that levels of carbon dioxide and other gases would continue to rise to more than twice their current level by 2100, as outlined in standard global-warming scenarios.

Eventually, the computer simulation showed, the number of extremely hot days during the growing and ripening season would increase by three to eight weeks in much of the South Central and Southwestern United States — too hot to produce premium wine grapes.

The number of cool days would also decline by more than three weeks in many regions of the country, opening up some areas for new grape production, but also increasing the possibility of more rot, mildew and fungus infections in those areas.

The West Coast would experience one of the biggest changes in season, resulting in a significant alteration to the quality of its grape harvest. Suitable grape-growing areas in California would shrink to a narrow coastal band, the researchers said, while premium wine-grape areas would shift into the Pacific Northwest and New England.

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