'Waste heat' from cities affects atmosphere
It’s well known that cities have their own microclimates, but new research has revealed the heat streaming from major metropolitan areas can affect the weather thousands of kilometers away.
The study, published in Nature Climate Change, shows how "waste heat" generated from buildings, cars, and other sources in major Northern Hemisphere cities causes winter warming across large areas of northern North American and northern Asia.
“What we found is that over Siberia, Eurasia and over part of Canada, temperatures in winter get about a degree warmer than what we saw in the past,” said lead author Guang Zhang of the Scripps Institution of Oceanography.
Using a computer model of the atmosphere, the authors found that the influence of this waste heat can also widen the jet stream and have an effect on the atmosphere.
"This is accomplished through atmospheric circulation change,” Zhang said.
The study also found that the changes to atmospheric circulation caused areas of Europe to cool by as much as 1 degree Celsius.
The researchers say around 40 percent of the world's total energy consumption comes from just 86 metropolitan areas in the Northern Hemisphere. Human-generated energy amounts to just 0.3 percent of the heat transported across higher latitudes by atmospheric and oceanic circulations. But the researchers say it’s impact comes from being highly concentrated.
“The world's most populated and energy-intensive metropolitan areas are along the east and west coasts of the North American and Eurasian continents, underneath the most prominent atmospheric circulation troughs and ridges," said co-author Ming Cai of Florida State University.
"The release of this concentrated waste energy causes the noticeable interruption to the normal atmospheric circulation systems above, leading to remote surface temperature changes far away from the regions where waste heat is generated."
The study’s authors say their discovery may explain why some regions are experiencing warmer winter weather than projected by climate computer models. They say in the future computer models need to be adjusted to take into account the influence of waste heat.