Global warming threatens West’s water resources
Water flow in the western U.S. has decreased for the last 20 to 30 years, but scientists have never understood why. Benjamin Santer of Livermore’s Program for Climate Model Diagnosis and Intercomparison and collaborators from the Scripps Institution of Oceanography have for the first time pinpointed humans as the cause of diminishing water flow on a regional scale. By looking at air temperature, river flow, and snowpack during the last 50 years, the team determined that the human-induced increase in greenhouse gases has seriously affected the water supply in the western U.S. “The water flow decrease is a result of temperature change,” says Scripps colleague Tim Barnett, “and that temperature change is caused by us.”

Santer and Barnett presented the research at the American Geophysical Union Meeting in December 2007. The team scaled down global climate models to a regional level and compared the results to their observations. The researchers found they could use the same models to predict the effects of the increase in greenhouse gases on the western U.S. in the future. By 2040, most of the snowpack in the Sierras and Colorado Rockies would melt by April 1 of each year because of rising air temperatures, causing a shift in river flows. With the existing greenhouse gas in the atmosphere, Earth will continue to warm for the next 80 to 100 years. “We are headed for a water crisis in the western United States, and it has already started,” says Barnett.
Contact: Benjamin Santer (925) 422-2486 (santer1@llnl.gov).

Human activities may shape California climate
Through research funded by the California Energy Commission, scientists from the Laboratory, the University of California at Merced, and the National Center for Atmospheric Research found that temperatures in California from 1915 to 2000 have increased by 1.16°C (2.1°F) statewide. The research, which appeared in the December 19, 2007, online edition of Climatic Change, also suggests that the warming may be related to human activities.

The team used data from up to eight observational records and found that warming has been fastest in late winter and early spring. “The trends in daily minimum and maximum temperatures over the last 50 and 85 years are inconsistent with current model-based estimates of natural internal climate variability,” says Livermore’s Céline Bonfils. “It’s pretty clear the increases are not the result of just natural causes. External factors such as greenhouse gases and urbanization come into play.” However, current climate models have not been effective in explaining California’s summertime trend, where warming mainly occurs at night. Previous research by the team indicates that large-scale irrigation in California has had a cooling effect on summer daytime temperatures, which may have counteracted warming from mounting greenhouse gases and urbanization. If this hypothesis is verified, the acceleration of carbon dioxide emissions combined with a leveling of irrigation may result in a rapid summertime warming in the Central Valley in the near future.

Researchers suggest that greenhouse warming will continue to influence climate and may have significant societal impacts in California. Benjamin Santer, also a member of the Livermore team, says, “Our study represents a credible first step toward identifying the effects of human activities on California’s climate.”
Contact: Céline Bonfils (925) 423-9923 (bonfils2@llnl.gov).

Stardust samples reveal unexpected results
Laboratory scientists, working with collaborators from other scientific and academic institutions, have unveiled new research on the dust collected from Comet Wild 2 during the Stardust mission. In a surprising turn of events, the research failed to find the primitive materials that had been thought to abound in comets. Rather, the dust from this particular comet formed very close to the young Sun and is more like material in asteroids. The research appeared in the January 25, 2008, edition of Science.

Researchers used Livermore’s aberration-corrected, monochromated, scanning transmission electron microscope known as SuperSTEM to analyze the Stardust samples. The samples were compared to interplanetary dust particles (IDPs) gathered from Earth’s stratosphere. Believed to be cometary dust, these IDPs contain the most primitive starting materials from which the planets in the solar system formed. Researchers were particularly interested in identifying in the Wild 2 dust two silicate materials unique to the IDPs, GEMS (glass with embedded metal and sulfides) and crystalline silicate enstatite (a rock-forming mineral). The team found only a single sliverlike whisker of enstatite, and it was similar to material in asteroids, not IDPs. Objects similar to GEMS were found, but the team determined they were created during the high-speed impact with Wild 2 dust.

The research emphasizes the continuum between asteroids and comets. “Wild 2 doesn’t match our idealized picture of a primitive comet made of ancient, unaltered material,” says Livermore scientist Hope Ishii. “The Stardust mission was a real success because without it, we never would have learned these things about our solar system. The returned sample is enabling us to continue to unravel how our solar system formed and evolved.”
Contact: Hope Ishii (925) 422-7927 (ishii2@llnl.gov).