Study suggests rise in heat waves by 2039

July 15, 2010, 12:31 a.m.

While skeptics brush off global warming as a distant catastrophe, a new Stanford study suggests that heat waves and extremely high temperatures could become commonplace in the United States by 2039.

After nearly two years of research analyzing computerized climate modeling, Noah Diffenbaugh, a professor of environmental Earth system science and a center fellow at the Woods Institute for the Environment, and former postdoctoral fellow Moetasim Ashfaq found that the number of heat waves per decade within the United States could rise within the next few decades.

“We were trying to see the potential danger of climate change within the envelope that global leaders decided was the threshold,” Diffenbaugh said.

In the 2009 Copenhagen Accord, global leaders agreed to consider action that would hold off the rise in global temperature to below 2 degrees Celsius. Despite this policy to limit global warming, the study indicates that even the two-degree limit on temperature increase does not avoid temporal extremes and heat intensification.

“We should have an aggressive target,” said Ashfaq, now a researcher at Oak Ridge Climate Change Science Institute. “Two degrees centigrade is not enough. If [we] keep it as a protocol issue and do not reach any agreement, and if we do not have a cap on those emissions, then there’s going to be a very drastic effect and severe consequences.”

The study also found data that supports an increase in exceedences — periods of warm weather hotter and longer than usual — throughout the next three decades. The study’s findings indicate that there will be three to four exceedences per decade over a large portion of the United States. The heat waves will also intensify, with up to eight exceedences per decade in the western United States and four per decade for the eastern United States from 2020 to 2029, according to the study.

Heat waves will hit the country across the board, but the western region of the United States will have to bear with the severest effects. Diffenbaugh and Ashfaq conducted their study based on data from the last 50 years.

“We did a high-resolution climate model experiment that’s not available for other regions of the globe with this kind of detail,” Diffenbaugh said, explaining why the study focused exclusively on the United States.

An important aspect of their work, according to Ashfaq, was the prediction of changes that would happen in the short term.

“What may happen in terms of temperatures and extremes is more important than what may happen by the end of the century,” he said, emphasizing the importance of answers to immediate events.

The study’s findings surprised Diffenbaugh and Ashfaq.

“I was surprised to see extreme hot events increase as much as they do so soon,” Diffenbaugh said.

“If you’re looking 100 years from now it’s not a big surprise,” Ashfaq said. “We are showing that it is going to happen in the near future, and this was a big surprise for us because we were not expecting an increasing number in the next few decades.”

Ashfaq added that the rise in heat waves could lead to what he calls “extreme” weather, which is “anything above normal, such as below or above normal temperature and a consistent anomaly for a long period [of time],” he said. “Extreme temperature is associated with extreme weather; anything beyond normal is going to have adverse effects on natural and human systems.”

A rise in the number of heat waves has an impact on human health and gives rise to more widespread heat-related illness.

“Severe temperatures and heat waves can cause excess mortality [as well as] many other effects,” Diffenbaugh said.

In 2003, a heat wave in Europe killed at least 35,000 people, according to the New Scientist journal.

Other effects could also have a drastic impact on the economy, including agriculture.

“Heat waves usually occur when you have less precipitation, [and a] rise in heat waves indirectly means a decrease in rainfall,” Ashfaq said. “It puts direct pressure on the economy because heat waves use more energy — people would turn toward using energy in terms of cooling equipment. This is going to put a lot of pressure on the existing setup.”

The recently published study was one that focused on heat waves and temperature, but is only one of a series of studies on global warming.

“Right now we’re doing a couple more,” Ashfaq said. “One is focused on the western United States’ snow cover and another is on precipitation.”

The duo is also studying potential changes to stream flow over the next 30 or 40 years.

According to Diffenbaugh, the team is also “continuing to try to understand the reliability of predictions on these regional and local scales over the next few decades.”

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