City heat changing the climate?

Monday 28th Jan 2013 by theWeather Club

Image: Storylanding

If you live in a city you may already be aware of the urban heat island effect that increases the temperature within the city by more than a few degrees compared to more rural locations due to way building materials effectively retain heat. However, a recent study has found that heat from major cities caused winter warming across large areas, thousands of miles away.

The study, published in the journal Nature Climate Change, looked at a number of major cities along the east coast of the US and found that winter warming was detected as far away as the Canadian prairies with an increase of 1°C due to the influence of big cities which produced changes in the weather systems, including the jetstream.

In populated regions, energy is consumed and dissipated into the atmosphere as heat and this anthropogenic heating could disrupt the normal atmospheric circulation pattern and produce a far-reaching effect on surface air temperature. The research identified the plausible climate impacts of energy consumption using a global climate model and found the surface temperature increased by 1°C in mid- and high latitudes in winter and autumn over North America and Eurasia. However, the study found that changes in atmospheric conditions had the opposite effect in Europe by lowering the autumn temperature by as much as 1°C.

The heat generated by major cities makes up just a small proportion of the warming caused by climate change or urbanisation but the study did help scientists account for additional warming that was not explained by existing climate models. "What really surprised us was that this energy use was a tiny amount, and yet it can create such a wide impact far away from the heat source," said Guang Zhang, a scientist at the Scripps Institution of Oceanography, who led the study. "We didn't expect it to be this much."