Cities are affecting weather thousands of kilometres away, study shows

Large cities have a wide reach impacting weather for thousands of kilometres.

A trio of researchers from two universities and the National Center for Atmospheric Research (NCAR) has published a study showing that waste heat produced from large metropolitan areas can have a significant effect on weather hundreds to thousands of kilometres away.

We've known about the 'urban heat island effect' — where the concrete and asphalt of cities absorb and retain more heat from the Sun than the surrounding 'natural' environment — for a long time now. However, there is another kind of urban heat — waste heat that is actually produced by the city, from the cars and trucks driving around in it and from the heating/cooling systems of the city's buildings.

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"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," said lead author Guang Zhang, who has a PhD in atmospheric physics from the University of Toronto, and currently works at the Scripps Institution of Oceanography, at UC San Diego in La Jolla, CA.

"This is accomplished through atmospheric circulation change."

Zhang, along with Dr. Ming Cai of Florida State University and NCAR scientist Aixue Hu, used computer models of the atmosphere along with models of waste heat from energy consumption, and found that this waste heat can influence the jet stream and other large atmospheric circulations, warming regions of northern and eastern Canada in the winter, and cooling areas of northern Europe and Asia in the fall.

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"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 Cai, according to Science Daily. "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, "Energy consumption and the unexplained winter warming over northern Asia and North America", was published in the journal Nature Climate Change on Sunday and shows that the heat produced by major cities in North America, which are responsible for roughly 40% of the world's energy consumption, can cause a temperature change of up to 1 degree C over the affected regions.

These results not only account for why some areas experience unexpected warming, but they also increase our overall understanding of how the atmosphere works and of the interconnections at play, which will allow climatologists to improve climate prediction models for the future.

(Image courtesy of NASA)

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