Cities' Waste Heat Can Raise Regional Temperatures: Study

New research shows that big cities can affect the regional climate around them, sometimes raising temperatures as much as 1.8 degrees Fahrenheit. Even if you live more than 1,000 miles away from the nearest metropolis, you could still be feeling the heat.

In a paper published Sunday in the journal Nature Climate Change, Aixue Hu of the National Center for Atmospheric Research and his colleagues examined the effects of “waste heat” generated by buildings, cars and other sources in major urban centers in the Northern Hemisphere. They used computer models of the atmosphere to look at how energy consumption and waste heat affects local temperatures.

“Earlier studies had suggested there was no significant impact of this heat on global mean temperature,” Hu said in a phone interview. “But what the previous studies didn't do is check the regional climate.”

Hu and his colleagues from the University of California, San Diego, and Florida State University found that the waste heat from North American and Asian cities was enough to cause extra winter warming, with some areas seeing an increase of as much as 1.8 degrees Fahrenheit. but changes to atmospheric circulation from waste heat had the opposite effect in Europe, with areas there cooling by as much as 1.8 degrees Fahrenheit, mostly in the fall.

"What we found is that energy use from multiple urban areas collectively can warm the atmosphere remotely, thousands of miles away from the energy consumption regions," co-author and Scripps researcher Guang Zhang said in a statement Sunday. "This is accomplished through atmospheric circulation change."

The scientists also saw that the waste heat can widen the jet stream, which may affect weather as well.

Though the amount of waste heat generated by humans pales in comparison to the heat from the sun, it is highly concentrated in metropolitan areas, which in the Northern Hemisphere tend to lie directly under major atmospheric troughs and jet streams.

The effect of urban heat on global mean temperatures is very small – an average worldwide increase of just about .02 degrees Fahrenheit, but locally, it can pack a stronger punch. The authors think climate models should take the influence of metropolitan waste heat into account.

“From this research we see that burning of fossil fuels can directly affect the lower atmosphere to generate regional patterns of warming and cooling,” Hu says.

SOURCE: Zhang et al. “Energy consumption and the unexplained winter warming over northern Asia and North America.” Nature Climate Change published online 27 January 2013.