HEAT generated by large cities can alter the climate thousands of miles away, research suggests.
The “waste heat” from buildings, factories and vehicles disrupts atmospheric systems that affect the weather over great distances, it is claimed.
This is said to have a significant regional impact, raising or lowering seasonal temperatures by up to 1C.
The effect may explain why some parts of the northern hemisphere are experiencing more winter warming than had been predicted by climate change scientists.
Some of the world’s most populated and energy-intensive urban centres lie beneath major circulation channels in the atmosphere.
They include the northern polar jet stream, a meandering “river” of high-altitude wind that blows around the Earth at more than 100mph.
Heat energy carried from cities by these circulation systems accounts for winter warming across large areas of northern North America and northern Asia, say scientists. In some remote areas, temperatures are pushed up by as much as 1C.
Meanwhile, the air over parts of Europe is made cooler, the research shows. Here, changes to atmospheric circulation caused by the waste heat can lead to 1C reductions in temperature, mostly in the autumn.
The findings, published in the journal Nature Climate Change, suggest that heat generated by cities can widen the jet stream.
“What we found is that energy use from multiple urban areas collectively can warm the atmosphere remotely, thousands of miles way from the energy consumption regions,” said lead scientist Dr Guang Zhang, from the Scripps Institution of Oceanography in California.
“This is accomplished through atmospheric circulation change.” Spread out across the world, the net average temperature increase produced by city waste heat is a negligible 0.01C. But at a regional level, the impact is significant, say the researchers.
Co-author Dr Aixue Hu, from the National Centre for Atmospheric Research in Boulder, Colorado, said: “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.
“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.”
The scientists analysed the energy consumption that generates waste heat. They calculated that in 2006, the world’s total energy consumption was 16 terawatts, or 16 trillion watts – the equivalent of leaving ten billion 100-watt lightbulbs on for a year.