From: Roger Greenway, ENN
Published January 28, 2013 06:02 AM

How Profoundly Cities Affect Temperatures Both Near and Far

It has been known for a long time that cities create warmer temperatures due to heat stored in buildings, roads, and other man-made structures. They also add heat from air conditioners, boilers, and other combustion sources. This is known as the urban "heat island". 

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What has not been known until now, is that cities also raise temperatures in the areas surrounding them, out thousands of miles. A new study shows the extent to which human activities are influencing the atmosphere, both locally, and at distant locations. Scientists have concluded that the heat generated by everyday activities in metropolitan areas alters the character of the jet stream and other major atmospheric systems. This affects temperatures across thousands of miles, significantly warming some areas and cooling others, according to the study this week in Nature Climate Change.

The extra "waste heat" generated from buildings, cars, and other sources in major Northern Hemisphere urban areas causes winter warming across large areas of northern North America and northern Asia. Temperatures in some remote areas increase by as much as 1 degree Celsius (1.8 degrees Fahrenheit), according to the research by scientists at the Scripps Institution of Oceanography; University of California, San Diego; Florida State University; and the National Center for Atmospheric Research.

At the same time, the changes to atmospheric circulation caused by the waste heat cool areas of Europe by as much as 1 degree C (1.8 degrees F), with much of the temperature decrease occurring in the fall.

The net effect on global mean temperatures is nearly negligible—an average increase worldwide of just 0.01 degrees C (about 0.02 degrees F). This is because the total human-produced waste heat is only about 0.3 percent of the heat transported across higher latitudes by atmospheric and oceanic circulations.

However, the noticeable impact on regional temperatures may explain why some regions are experiencing more winter warming than projected by climate computer models, the researchers conclude. They suggest that models be adjusted to take the influence of waste heat into account.

Urban road in the evening photo via Shutterstock.

Read more at UCAR.

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