Research Highlight: Once-Ultrarare Heatwaves Could Become Common, Scripps Researchers Tell California Energy Community

In the past 60 years, California has experienced two heatwaves – in 1955 and 2006 – in which temperatures in its urban centers were greater than 37.8 degrees C (100 degrees F) for three or more consecutive days.

The latter episode, studied extensively by Scripps Institution of Oceanography, UC San Diego climate researcher Alexander Gershunov, led directly to the deaths of an estimated 400-600 people and cost the state $5.4 billion just in costs related to the health impacts the event caused.

A new analysis prepared by other Scripps researchers indicates that by century’s end, those kinds of heatwaves will be the norm. Scripps climate researcher David Pierce said the new data will be assimilated into a major climate report scheduled for release in 2013. But on April 30, Pierce and fellow Scripps climate researcher Dan Cayan gave the California energy community a preview.

“We’ll start getting these kinds of heatwaves more frequently by 2020 and by 2070, they’ll become common,” Pierce said.

Pierce emphasized that all models have uncertainty. For example, the effect of climate change on California’s coastal marine layer is not well resolved by the current crop of global models.

“That matters because the marine layer makes a big difference to energy use, since so many people live near the coast,” he said, “but the new models are the best look we have yet at what the future climate is likely to hold.”

Pierce downscaled several global models to the California region, and looked at temperatures weighted by where people in California live. In all scenarios, not only do episodes of 100-degree-plus temperatures happen more frequently, but events in which temperatures top 100 for seven or more days begin happening at least once a decade by 2060 in all the models.

Pierce said the data will be submitted for possible inclusion in the latest report of the Intergovernmental Panel on Climate Change, which will be issued in four parts in 2013 and 2014. The United Nations-sponsored entity, which provides a periodic synthesis of international climate research, shared the Nobel Peace Prize with former U.S. Vice President Al Gore after releasing its Fourth Assessment Report in 2007.

Cayan and Pierce have been delivering the long-view message represented by Pierce’s heatwave analysis to utility managers conditioned to prepare for short-term weather trends, but Cayan said that over several years of such meetings, the perspective of scientists and resource managers has steadily converged.

“One of the important aspects of this is that (utilities) educate us on what are the critical climate and environmental factors that influence how they operate,” said Cayan. “This is not a one-way broadcast but a two-way conversation.”

The workshop hosted by the California Energy Commission addressed other climate-change issues of growing concern to cities and utilities such as sea-level rise and decreases in hydropower and water availability.

“A lot of these changes are not going to reverse, they’re only going to compound,” Cayan said.

– Robert Monroe

Related Image Gallery: California Heatwave Scenarios