updated 8/17/2004 10:00:01 AM ET 2004-08-17T14:00:01

Global warming could cause dramatically hotter summers and a depleted snow pack in California, leading to a sharp increase in heat-related deaths and jeopardizing the water supply, according to a study released Monday.

The report is substantially more pessimistic than previous projections, and was dismissed by one expert as “another piece of climate alarmism.”

The study, published in the Proceedings of the National Academy of Scientists, focused on California because of its diverse climate, large economy, agricultural interior, and profuse pollution from industries and population centers.

The researchers used computer models they said illustrate the consequences of doing nothing, or adopting “relatively aggressive” policies such as the greater use of renewable energy sources rather than fossil fuels.

California can avoid the worst effects by quickly cutting how much carbon dioxide and other heat-trapping gases are released into the atmosphere, the scientists said.

Call to action
The 19 scientists who prepared the report include experts from Stanford University and the University of California, Berkeley, along with consultants and members of the Union of Concerned Scientists.

“If we do not take action now to reduce emissions of greenhouse gases, the consequences for California after about 2050 will become significantly more harmful than if we do take action now,” said Michael Hanemann, director of the California Climate Change Center at UC Berkeley.

Interactive: The greenhouse effect Under the most optimistic computer model, periods of extreme heat would quadruple in Los Angeles by the end of the century, killing two to three times more people than in heat waves today; the Sierra Nevada snow pack would decline by 30 percent to 70 percent; and alpine forests would shrink 50 percent to 75 percent.

The most pessimistic model projects five to seven times as many heat-related deaths in Los Angeles, with six to eight times as many heat waves. Snow pack and high altitude forests would shrink up to 90 percent.

The scientists’ temperature projections are higher than previous estimates, particularly in summer. Their predictions of an extreme decline in snow pack, alpine forests and the spread of desert areas all exceed earlier projections.

Skeptic sees 'alarmism'
“It’s another piece of climate alarmism,” said Marlo Lewis, a senior fellow at the Competitive Enterprise Institute. “It’s layers of assumptions and it’s all designed to paint a very frightening picture.”

He and Bonner Cohen, a senior fellow at the National Center for Public Policy Research, questioned the reliability of the computer models, and said the report fails to account for human ingenuity and adaptability.

Among other predictions, the report says spring melt-off will come earlier, increasing the risk of flooding and decreasing how much snow-melt could be captured in reservoirs. The state will rely more on increasingly scarce groundwater, even as droughts become more frequent and more severe.

Also, the state’s renowned wine industry could suffer everywhere except on the coast, the scientists say — countering previous projections that at least the wine might improve.

The full report is online at www.pnas.org/cgi/doi/10.1073/pnas.0404500101.

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