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October 4, 2004
Hotter Summers in Store for California
(But There is a Choice)

One hundred years from now, summers in Los Angeles may be as scorching as summers in the Mojave Desert. But it doesn't have to be that way, according to a team of 19 scientists that includes Berkeley Lab's Norman Miller and Larry Dale.

If no measures are taken, summers in Los Angeles could be as hot as those in the Mojave desert by next century, according to a recent study.

In a study published in the August 24 issue of the Proceedings of the National Academy of Sciences, the research team predicted that Californians could experience substantially hotter summers by the end of the century, which may lead to an increase in heat-related deaths and water and energy shortages. Just how hot depends on what's done between now and then.

The researchers analyzed two greenhouse gas emission scenarios recently presented by the Intergovernmental Panel on Climate Change, a United Nations-formed organization that informs the world's policymakers on climate change and impacts. One scenario assumes an energy-use trajectory similar to the present course, meaning rapid introduction of new technologies, extensive economic globalization, and a fossil-intensive energy path. Under this scenario, there may be six times the 1990 levels of carbon dioxide in the atmosphere by 2100, causing summer temperatures in California to soar as high as 18 degrees Fahrenheit above current temperatures.

The other scenario takes into account the adoption of green alternatives such as fuel-efficient technologies, a stronger role of local governments in fostering environmentally friendly policy, and a rapid transition to service and information economies. Under this scenario, atmospheric carbon dioxide levels peak at double 1990 levels by midcentury, then slowly decline to below current-day levels. Summer temperatures in California only rise between 4 and 5 degrees Fahrenheit by 2100.

"These aren't the absolute worst and best case scenarios," says Miller of Berkeley Lab's Earth Sciences Division. As co-authors of the paper, Miller and Dale, who is in the Environmental Energy Technologies Division, conducted analyses related to heat waves, temperature extremes, water resources, and snowmelt using projections from two state-of-the-art climate models with low and medium sensitivity.

"But one of the purposes of this study is to let people know there is a choice," says Miller. "Our energy policy in the U.S. has consequences, and we have an influence on those consequences."

The study comes as a confusing mix of global warming-related fact and fiction bombards the public. It's the cover story of this month's edition of National Geographic Magazine, in which strong evidence of global climate change is presented. And people flocked to multiplexes this summer to see an unrealistic action movie, The Day After Tomorrow, in which abrupt climate change triggers tsunamis and ice ages. Although the Statue of Liberty won't be engulfed by a giant wave if high fossil fuel emission continues unchecked, the projections presented in the study don't necessarily soften the blow.

If energy use continues as usual, the Sierra snowpack could decline between 70 and 90 percent by 2100.

According to the study, in the fossil fuel intensive scenario, Los Angeles may experience up to six times more heat waves each summer toward the end of this century, with heat related mortality increasing five to seven times. In addition, by 2100 the Sierra snowpack could decline between 70 percent and 90 percent from current levels, which would fundamentally disrupt California's water rights system.

But the study also projects that if energy efficient technologies are given a chance, and local governments take a lead role in implementing responsible energy policy, Los Angeles heat waves will only quadruple in frequency, heat related mortality rates will only double or triple, and between 30 percent and 70 percent of the Sierra snowpack will vanish.

"This is a good opportunity for California government to demonstrate its leadership role in environmental policy," says Miller. "If the state can commit to change, the nation will follow."

In addition to Berkeley Lab, researchers from several universities and research institutions contributed to the study, including Stanford University, the University of California at Berkeley, the Scripps Institution of Oceanography, and the National Center for Atmospheric Research. Katharine Hayhoe of South Bend, Indiana-based ATMOS Research and Consulting is the lead author.

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