Scorching Summer Forecast Sees Ten-Degree Rise by 2080

Brian Handwerk
for National Geographic News

May 10, 2007

Residents of the eastern United States may see average summer temperatures rise by 10 degrees Fahrenheit (5.5 degrees Celsius) during the next 80 years, a new NASA study suggests.

The culprit is greenhouse gas emissions—the release of gases linked to global warming—the report says.

(Related: "Global Warming: How Hot? How Soon?" [July 27, 2005].)

"There is the potential for extremely hot summertime temperatures in the future, especially during summers with less-than-average frequent rainfall," said lead author Barry Lynn of NASA's Goddard Institute for Space Studies and Columbia University.

Eastern U.S. states currently average summer daily highs in the low to mid-80s Fahrenheit (27 to 30 degrees Celsius).

But the new research suggests that average high temperatures could reach the low to mid-90s Fahrenheit (32 to 36 degrees Celsius) in a typical summer by the 2080s.

In extremely dry years, Chicago; Washington, D.C.; Atlanta; and other cities could experience July and August daily highs between 100 and 110 degrees Fahrenheit (37.8 to 43.3 Celsius).

NASA's model incorporated three decades of temperature and rainfall observations to estimate future rainfall totals. It also took into account the time of day when precipitation is likely to occur—a key factor in how much rain falls and cools off the Earth.

(Interactive graphic: how global warming works.)

Sweat Locally

Jay Gulledge is a senior research fellow at the Pew Center on Global Climate Change outside Washington, D.C.

While the study's temperature-change numbers may seem shocking, Gulledge said, they simply represent a different kind of model.

"We're not used to hearing numbers like these, because we're not used to looking at things on a regional scale," he said.

"What we always hear about is an average, most often a global average. [That average] usually includes land and sea temperatures, which results in a lower number than land only," Gulledge added.

"It's typically annual, so you end up with both winter and summer [projections] in there. So ten degrees really sounds about right to me" for summer temperatures on land, Gulledge said.

Heated Debate

The report is sure to heat up an already boiling debate on the possible causes and likely effects of climate change.

Rapid environmental change would force all species in the region to adapt—including humans.

"Any drastic change in weather has the potential to negatively affect agricultural production in the U.S. and could seriously affect the growing season," National Farmers Union President Tom Buis said.

"We are very concerned that if these issues are not addressed to offset the impact of global warming, not only will farmers and producers be affected, but so will the consumers who rely on American crops."

Peter Stone, a climate scientist at the Massachusetts Institute of Technology, sounded a cautionary note about assumptions made on the results of single model.

"There is a wide range of possible scenarios and large differences between different models' projections for a given scenario," Stone said. "Furthermore, this particular [model] did not do well in simulating trends in summer temperatures during the test period, 1977 to 2004.

"Given all the substantial uncertainties, any objective analysis would conclude that this particular outcome has a rather low probability," Stone continued.

"It could turn out either better or worse. Any projections like this, to be truly useful, should have error bars attached to them," he added. "In this case those error bars would be very large."

The new model assumes that carbon dioxide emissions will continue to rise at their current rate: some 2 percent each year. That raises hopes that, if humans reduce greenhouse gas emissions, the extreme scenario could still be avoided.

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