[californiadisasters] More Calif. Heat Waves by 2020

Scientists: more Calif. heat waves by 2020

May 14th, 2012, 5:27 pm - posted by Pat Brennan, O.C. Register science & environment editor

Strings of days when temperatures spike over 100 degrees should become more frequent in California by 2020, and commonplace 50 years after that, according to recent computer modeling results from scientists at the Scripps Institution of Oceanography.

Several computer models, including some with finer-grained climate data than in years past, show that global warming expected in coming decades will translate into a greater chance of potentially deadly heat waves — not unlike a 2006 California heat wave that killed an estimated 400 to 600 people.

"All the models are essentially pushing their daily distributions of temperature to the warm side," said Dan Cayan, a regional climate researcher at Scripps who also works for the U.S. Geological Survey. "So we're seeing more frequent and, actually, more intense extremes."

And that frequency increases in the latter part of the 21st century, he said, perhaps even becoming common by 2070.

While other climate scientists have said they would expect heat waves to increase as the climate warms, this was among the first efforts to gauge the possible range of effects in urban areas using the newer, more precise modeling data.

Cayan and fellow Scripps climate researcher David Pierce saw a rise over time in what is now a rare type of heat wave –when temperatures reach 100 degrees or higher over three or more consecutive days. In California, such heat waves have occurred only twice in the state's urban centers in the past 60 years, in 1955 and in 2006.

All the models produced heat waves of seven or more 100-degree days occurring once a decade by 2060.

The scientists used a statistical process called "downscaling" that matched global computer models of climate with measured, local variability in temperature across California to produce estimates of how frequently heat waves might occur in years ahead.

As with all computer modeling, Cayan said, the results come with some uncertainties. The unpredictability of the effects of warming on the coastal marine layer, for example, means that estimating temperature trends along the coast is problematic.

That also affects coastal cloudiness, another complication.

"We are still sort of scratching our heads to understand how this coastal zone in California is going to react as the broad-scale climate changes," he said.

The scientists relied on data gathered in preparation for the next global climate report from the Intergovernmental Panel on Climate Change, expected in 2013 and 2014.

While the scientists expect to publish their results, it is uncertain whether they'll end up being part of the IPCC report.

But they gave an early glimpse to the California Energy Commission during a climate workshop last month.

The workshop also took up other climate change questions that cities and utilities might face, including rising sea levels and potential tightening of water supplies.

Source: http://sciencedude.ocregister.com/2012/05/14/scientists-more-calif-heat-waves-by-2020/171637/

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