* Burning fossil fuels in urban areas changes air currents
* City heat hitches a ride over vast areas of Northern
By Environment Correspondent Deborah Zabarenko
WASHINGTON, Jan 27 The energy big cities burn -
mostly coal and oil to power buildings, cars and other devices -
produces excess heat that can get into atmospheric currents and
influence temperatures thousands of miles (km) away, a new study
The so-called waste heat that leaks out of buildings,
vehicles and other sources in major Northern Hemisphere cities
makes winters warmer across huge swaths of northern Asia and
northern North America, according to a report published on
Sunday in the journal Nature Climate Change.
That is different from what has long been known as the
urban-heat island effect, where city buildings, roads and
sidewalks hold on to the day's warmth and make the urban area
hotter than the surrounding countryside.
Instead, the researchers wrote, the excess heat given off by
burning fossil fuels appears to change air circulation patterns
and then hitch a ride on air and ocean currents, including the
The burning of fossil fuels also sends climate-warming
carbon dioxide into the atmosphere, contributing to global
But study author Aixue Hu of the National Center for
Atmospheric Research in Colorado said in a statement that the
excess heat generated by this burning in cities could change
atmospheric patterns to raise or lower temperatures far afield.
Some remote locations heat up by as much as 1.8 degrees F (1
degree C) as a result, the study said. But some parts of Europe
cool off a bit, especially in autumn, because of the way urban
waste heat changes atmospheric circulation.
The impact on global mean temperature is negligible, because
the total amount of waste heat from human activities is only
about one-third of one percent of the total amount of heat
carried across high latitudes by air currents and oceans.
But this waste heat from cities and the way it moves around
could help explain why some places are warmer in winter than
climate computer models predict, the researchers said, and
suggested that these models be adjusted to take this effect into
"We have seen this global warming of the high-latitude
regions over the last 50 years," the study's lead author, Guang
Zhang of the Scripps Institution of Oceanography, said by
telephone. "But the computer models to date have not been able
to account for all the warming observed."
By adding the influence of big cities' waste heat to their
computer simulations, the researchers were able to find a likely
cause for all that extra warmth, Zhang said.
(Reporting By Deborah Zabarenko)