Post by POA on Aug 27, 2004 4:25:11 GMT -5
CALIFORNIA
Global warming clouds the future
But experts say it's not too late to cut harmful emissions
Carl T. Hall, Chronicle Science Writer
Tuesday, August 17, 2004
A fresh look at California's climate future suggests some profound changes may be coming as global warming takes hold, including extended heat waves in Los Angeles, disrupted ecosystems in the mountains and chaos in California's water-supply system.
Researchers adapted two of the latest computer models of global climate change to determine how California might be affected under two different scenarios -- one optimistic and one pessimistic -- for emissions of heat-trapping greenhouse gases.
Although the scientists steered clear of making any specific pronouncements on policies or politics, their study, which was published online Monday in the Proceedings of the National Academy of Sciences, sets a new benchmark for evaluating California's stake in the global-warming debate.
Nineteen scientists took part, many of them donating their time, including California climate experts Daniel Cayan of the Scripps Institution of Oceanography, Stephen Schneider of Stanford University and R. Michael Hanemann of UC Berkeley.
The Union of Concerned Scientists in Washington, D.C., contributed researchers and financing for the lead author, Katharine Hayhoe, an atmospheric scientist at ATMOS Research and Consulting in South Bend, Ind.
During a telephone briefing Monday, Hayhoe and colleagues said conservation practices today could have a big effect on climate conditions in 50 or 100 years.
Researchers deliberately chose not to evaluate the merits of any particular policy option, but they called on the U.S. government, as well as American businesses and individual citizens, to take a leadership role in putting the world on a course to reduce harmful emissions. They said it's clear something needs to be done, and soon, to cut the emissions they said are clouding both the atmosphere and California's economic future.
"Unless we take steps now, the consequences after 2050 will be significantly worse," Schneider said. California's arid nature -- and its weather-dependent industries, from skiing to wine-making -- dramatically highlight the effects of climate change.
The scientists compared data for the period 1961-1990 with projections for 2020-2049 and for 2070-2099. Under the more optimistic scenario, the results showed that average temperatures in the state would rise by roughly 4 to 6 degrees Fahrenheit by the end of the century compared with the 1961-1990 base period, if the computer models are accurate.
That might not seem cataclysmic. But Hayhoe said it would still be enough to make Yosemite Valley feel more like downtown Sacramento in the summer, and trigger profound ecological effects.
If it's worse than that, the annual temperature averages could jump by 7 to 10 degrees. It could be a whopping 15 degrees warmer in summer. That would make California's balmy coastal cities feel more like hot inland towns do now, while "inland cities would feel like Death Valley does today," Hayhoe said.
Daily life in Los Angeles already includes about a dozen "heat-wave days" a year, defined as three or more days in a row when temperatures climb above 90 degrees. Under the worst-case heating outlook, there would be as many as 95 such days by the end of the century, producing about 1,400 more heat-related deaths.
In the mountains, snowpack by April 1 would diminish to nearly nothing at the lower and middle elevations, with up to a two-thirds reduction above the 9,000-foot level. That would have a devastating impact on the state's water system, since the Sierra snowpack serves essentially as a gigantic reservoir for downstream water systems.
This would allow some species of plants and animals to extend their range to higher elevations. At the same time, it would "squeeze high-altitude ecosystems right off the tops of the California mountains," said Christopher Field, a study co-author and director of the Carnegie Institution's Department of Global Ecology, located at Stanford.
Reduced water availability would more than cancel out any advantage from longer growing seasons. The state's prestige wine growers would take a hit, because the hotter summers would cause the premium varietals to mature too quickly.
Despite the widespread consensus among climate researchers that global warming is a genuine problem, a few scientists suggest climate-change worries might be overblown.
A report last week in the journal Geophysical Research Letters, for example, claimed that satellite readings have found no evidence of a warming trend, and that surface temperature data are not reliable measures of long-term climate change. Counterbalancing natural factors also may reduce temperatures and prove all the forecasts and computer models wrong, scientists say.
But most experts agree there is little doubt that worldwide average temperatures already have increased measurably -- roughly 1 or 2 degrees Fahrenheit during the past century -- and are headed higher, almost certainly as a result of greenhouse gas emissions.
E-mail Carl Hall at chall@sfchronicle.com.
