City heat affecting temperatures thousands of kilometres away

Heat generated by everyday activities in major cities affects temperatures across thousands of kilometres, significantly warming some areas and cooling others, according to a new study.

The '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, US scientists found.

The impact on temperatures may explain a climate puzzle of sorts: why some areas are experiencing warmer winters than predicted by climate models, researchers said.

The study found that temperatures in some remote areas increase by as much as 1 degree Celsius. At the same time, the changes to atmospheric circulation caused by the waste heat cool areas of Europe by as much as 1 degree Celsius.

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

The waste heat is also changing atmospheric circulation,including jet streams - powerful narrow currents of wind that blow from west to east and north to south in the upper atmosphere, LiveScience reported.

In the new study, the researchers looked at "urban heat", produced directly by transportation, heating and cooling units, and other energy-consuming activities.

"The burning of fossil fuel not only emits greenhouse gases, but also directly affects temperatures because of heat that escapes from sources like buildings and cars," said study researcher Aixue Hu, of the National Center for Atmospheric Research (NCAR).

"Although much of this waste heat is concentrated in large cities, it can change atmospheric patterns in a way that raises or lowers temperatures across considerable distances," Hu said.

The team studied the energy effect using the NCAR model and ran it with and without the input of human energy consumption, to see whether it could account for large-scale regional warming.

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