Climate Warming in California Could Be Aggravated by More Frequent Dry Years

American Geophysical Union, Fall Meeting 2008

The latest generation of global climate model (GCM) projections, run under different greenhouse gas-emission scenarios, provides a set of possible scenarios for California's climate. According to scientists at Scripps Institution of Oceanography at UC San Diego and colleagues, all of the model simulations depict substantial warming over the 21st Century. Although precipitation changes are not as certain, the consensus of 12 different models produces a reduction in precipitation over California.

Reductions in precipitation are found throughout most of California in both the lower and higher greenhouse gas scenarios that were examined, but the drying is greater in the higher emissions-scenario simulations. Drying is greater in Southern California than Northern California. Progressively warmer and longer summers that develop over the 21st Century would place further stresses on water supply.

Dan Cayan, a Scripps climate researcher who also works for the U.S. Geological Survey, will present the latest evidence and projections of climate change effects ranging from sea-level rise and desertification to impacts on water supply in "Climate Change in California - Why is this region especially vulnerable?" The talk will be part of a series of presentations assessing regional global warming vulnerabilities and adaptation strategies. (Tuesday, Dec. 16, 10:20 a.m. · Moscone Center 2007)

Cayan notes that the tendency toward drier conditions will be compounded by the loss of snow and diminished Sierra Nevada water storage in spring and early summer. Additionally, recent analysis has revised estimates of sea level rise by 2100 to between 0.5 meters (20 inches) to more than 1 meter (39 inches), increases that are greater than estimates made just a few years ago. Cayan will discuss how combinations of sea-level rise and Sierra Nevada floods could impact the San Francisco Bay and Sacramento/San Joaquin River Delta, a complex estuary that supplies fresh water for California agricultural, commercial and domestic users.

This work is part of a recent effort by a large team of scientists to assess impacts of climate change on California's economy, ecosystems and other human and natural resources. Cayan and colleagues from Scripps and other institutions have also collaborated on papers presenting a new regional analysis focused on the western United States. The research indicates that warming and associated hydrological trends are not likely to have been caused solely by natural climate variability. These trends include winter and spring warming, a decline in frost days, lower spring snowpack and advances in the timing of snowmelt runoff. The observed trends appear to result, at least in part, to the combined effects of anthropogenic greenhouse gases and aerosols. The presentation will include researchers from Scripps, Lawrence Livermore National Laboratory, University of Washington and Japan's National Institute for Environmental Studies.


Related presentations by Cayan and colleagues:
GC33C-01 · Wednesday, Dec. 17, 1:40 P.M. · Moscone Center 2007
"Anthropogenically induced changes in temperature and implications for water resources in the western
United States"

GC43C-0744 · Thursday, Dec. 18, 1:40 p.m. · Moscone Center Hall D
"Aridity and climate change in the western U.S."

GC43C-0745 · Thursday, Dec. 18, 1:40 p.m. · Moscone Center Hall D
"Increased flood risks in the Sacramento-San Joaquin Valleys, CA under climate change"