News in Science

Cities affect weather over long distances

Long reaching impact A team of climate modellers have found that the heat used to warm a city in the middle of winter can affect the weather patterns of areas up to a thousand kilometres away.

Despite the fact that heating energy in big cities is sparsely dispersed over the planet as a whole - amounting to only about 0.3 per cent of the total energy coming from warmer regions to cooler regions in winter via weather and ocean currents - this human-made heat could be enough to affect the jet stream and other big atmospheric circulation systems. This means big heated cities could be altering the weather thousands of miles away in the winter.

That's the conclusion of a group of researchers from Scripps Institution of Oceanography, Florida State University, and the National Center for Atmospheric Research.

The researchers added the anthropogenic winter heat to climate models to test out whether it could explain real world winter warming patterns seen in some areas that had before confounded scientists.

The results of the study appear online in the journal Nature Climate Change.

Specifically, these researchers find evidence that the waste heat from buildings and cars in urban areas of the Northern Hemisphere are increasing temperatures in remote areas by as much as 1°C in remote areas of North America and northern Asia.

The effect in Europe is different, however, with the heat altering patterns so that things get colder by the same amount in the autumn. Globally, the winter heating only contributes 0.01°C, which is certainly tiny. But in this case, it's more a matter of how a little bit of concentrated heat goes a long way in terms of disrupting the atmosphere.

"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," says NCAR scientist Aixue Hu and co-author of the study.

"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."

Does this mean we should stop heating our homes? Not necessarily. But it does suggest that lowering the heating thermostat has an added, direct benefit.