Hot Cities Make Environment Hotter
31 January, 2013
Huge US east coast cities generate extra heat that affects habitats thousands of miles away. This adds additional warming not explained by existing climate models. In parts of Asia, this pattern was also found.
Scientists Guang J. Zhang, Ming Cai & Aixue Hu found :
The worldwide energy consumption in 2006 was close to 498 exajoules. Although energy consumption is sparsely distributed over the vast Earth surface and is only about 0.3% of the total energy transport to the extratropics by atmospheric and oceanic circulations, this anthropogenic heating could disrupt the normal atmospheric circulation pattern and produce a far-reaching effect on surface air temperature.
They identified the plausible climate impacts of energy consumption using a global climate model.
They concluded that energy consumption is probably a missing forcing for the additional winter warming trends in observations.
Suzanne Goldenberg, the Guardian’s US environment correspondent  reported:
Those who wonder why large parts of North America seems to be skipping winter have a new answer in addition to climate change: big city life.
A study, published in the journal Nature Climate Change, found that the heat thrown off by major metropolitan areas on America's east coast caused winter warming across large areas of North America, thousands of miles away from those cities.
Winter warming was detected as far away as the Canadian prairies. In some remote areas, temperature rose by as much as 1 degree C under the influence of big cities, which produced changes in the jet stream and other atmospheric systems, the study found.
Researchers found a similar pattern in Asia, where major population centers resulted in strong warming in Russia, northern Asia, and eastern China.
On the flip side, however, changes in atmospheric conditions had an opposite effect in Europe – lowering autumn temperatures by as much as 1 degree C.
The extra heat generated by big cities was just a fraction of the warming caused by climate change or urbanisation, the researchers said. 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."
Global temperature averages were barely affected by the big city heat, barely .01C on average. But big cities had a noticeable impact on regional temperatures almost on a continental scale.
Researchers said the extra heat should be taken into account in future climate projections.
Scientists have for years been trying to untangle how big cities – with the sprawl of buildings and cars – affect climate.
The study suggests cities themselves have far-reaching effects on climate, in addition to the climate pollution caused by the burning of fossil fuels.
In another report  Steve Connor said:
The waste heat generated by large cities can affect temperatures in areas hundreds of miles away by changing wind patterns in the upper atmosphere, a study has found.
Scientists have estimated that the heat released into the atmosphere from buildings, cars and factories could play a significant role in the warming – and the cooling – of locations in other countries.
Using computer models of how heat is transported around the globe, the study published in the journal Nature Climate Change says that waste heat from 86 urban centers in the northern hemisphere could in theory raise temperatures of parts of North America and northern Asia by as much as 1C.
The same models suggest that other parts of the northern hemisphere, notably Europe, could actually become cooler at certain times of the year by up to 1C as a result of the heat affecting the direction of high-altitude winds such as the jet stream.
 Nature Climate Change, (2013), doi: 10.1038/nclimate1803, Jan 27, 2013,
 guardian.co.uk, Jan 27, 2013, “Heat from North American cities causing warmer winters, study finds”, http://www.guardian.co.uk/science/2013/jan/27/scienceofclimatechange-climate-change
 The Independent, Jan 27, 2013, “Wasted heat from large cities affects temperatures in distant regions”, http://www.independent.co.uk/environment/climate-change/wasted-heat-from-large-cities-affects-temperatures-in-distant-regions-8468955.html
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