US should prepare for many more heatwaves, says government-funded report

Posted by Emma Woollacott

Heat waves like the one now roasting the Eastern Seaboard are likely to become commonplace over the next 30 years, say scientists at Stanford University - even if global temperatures rise by only one degree Celcius.   

"Using a large suite of climate model experiments, we see a clear emergence of much more intense, hot conditions in the US within the next three decades," said Noah Diffenbaugh, an assistant professor of environmental Earth system science at Stanford.

"Those kinds of severe heat events also put enormous stress on major crops like corn, soybean, cotton and wine grapes, causing a significant reduction in yields."

The study follows a recent NASA report which concluded that the previous decade, January 2000 to December 2009, was the warmest on record.

The team used two dozen climate models to project what could happen in the US if increased CO2 emissions raised the Earth's temperature by one degree Celcius between 2010 and 2039 – more than likely, according to the International Panel on Climate Change.

Many climate scientists and policymakers have targeted a two-degree C temperature increase as the point at which the planet is likely to experience serious environmental damage.

But that may be too high, said Diffenbaugh.

"Our results suggest that limiting global warming to two degrees Celsius above preindustrial conditions may not be sufficient to avoid serious increases in severely hot conditions," he said.

The researchers analyzed temperature data for the continental US from 1951-1999. Their goal was to determine the longest heat waves and hottest seasons on record in the second half of the 20th century.

Those results were fed into an ensemble of climate forecasting models, including the high-resolution RegCM3, which is capable of simulating daily temperatures across small sections of the US.

"This was an unprecedented experiment," Diffenbaugh said. "With the high-resolution climate model, we can analyze geographic quadrants that are only 15.5 miles to a side. No one has ever completed this kind of climate analysis at such a high resolution."

The results were surprising. According to the climate models, an

intense heat wave – equal to the longest on record from 1951 to 1999 – is likely to occur as many as five times between 2020 and 2029 over areas of the western and central United States.

The 2030s are projected to be even hotter.

The Stanford team also forecast a dramatic spike in extreme seasonal temperatures during the current decade. Temperatures equaling the hottest season on record from 1951 to 1999 could occur four times between now and 2019 over much of the US, according to the researchers.

"Frankly, I was expecting that we'd see large temperature increases later this century with higher greenhouse gas levels and global warming," Diffenbaugh said. "I did not expect to see anything this large within the next three decades. This was definitely a surprise."

"It's up to the policymakers to decide the most appropriate action," Diffenbaugh said. "But our results suggest that limiting global warming to two degrees C does not guarantee that there won't be damaging impacts from climate change."

The research was supported by the US Department of Energy and the National Science Foundation.