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‘Waste heat’ from big cities affects temperatures for thousands of miles, says study

Large cities may be affecting the weather of cities more than 1,000 miles away. That is the conclusion reached by scientists from Scripps Institution of Oceanography, Florida State University and the National Center for Atmospheric Research, according to a news release from the University Corporation for Atmospheric Research.

In a new study that reveals the level to which human activities are affecting the atmosphere, climate scientists have concluded that the heat created by everyday activities in major cities changes the character of the jet stream and other major atmospheric systems. These changes can affect temperatures across thousands of miles, warming some areas and cooling others.

The extra “waste heat” generated from buildings, cars and other sources in major Northern Hemisphere cities leads to winter warming across large areas of northern North America and northern Asia. According to scientists, temperatures in some remote areas increase by as much as 1.8 degrees Fahrenheit. However, changes to atmospheric circulation due to waste heat cool areas of Europe by as much as 1.8 degrees Fahrenheit (much of this temperature decrease takes place in the fall.)

The net effect on global mean temperatures is an average increase worldwide of approximately 0.02 degrees Fahrenheit. According to scientists, this is because the total human-produced waste heat is only about 0.3 percent of the heat moved across higher latitudes by atmospheric and oceanic circulations.

Scientists conclude that the noticeable effect on regional temperatures may illustrate why some regions are seeing more winter warming than projected by climate computer models. They argue that the models must be altered to take the impact of waste heat into account.

“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 co-author Aixue Hu, a scientist at the National Center for Atmospheric Research. “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.”

According to scientists, waste heat is different from the so-called urban heat island effect. These islands are primarily a function of the heat gathered and re-radiated by pavement and buildings, whereas waste heat is generated directly though transportation and other activities.

Hu and his colleagues looked at the energy consumption that creates waste heat release. They calculated that the world’s total energy consumption is 2006 was equivalent to a constant-use rate of 16 terawatts. They contend that of 16 TW, an average rate of 6.7 TW was consumed in 86 major cities in the Northern Hemisphere.

Hu and his colleagues discovered that the influence of this waste heat 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 away from the energy consumption regions,” says lead author Guang Zhang of Scripps Institution of Oceanography. “This is accomplished through atmospheric circulation change.”

Scientists point out that the release of waste heat is different from solar energy, which warms Earth’s surface and is redistributed by atmospheric circulation from one region to another. They also note that human-generated energy is highly concentrated in urban areas.

“The world’s most populated and energy-intensive metropolitan areas are along the east and west coasts of the North American and Eurasian continents, underneath the most prominent atmospheric circulation troughs and ridges,” says Ming Cai of Florida State University. “The release of this concentrated waste energy causes the noticeable interruption to the normal atmospheric circulation systems above, leading to remote surface temperature changes far away from the regions where waste heat is generated.”

However, the U.S. Department of Energy makes the case that waste heat can be captured, converted and reused for useful purposes. Although the DOE primarily cites the energy and cost savings of waste heat recovery for industrial facilities, perhaps certain methods of waste heat recovery will someday be available on a larger scale to mitigate the effects of waste heat from major cities on areas thousands of miles away.

The study’s findings were recently described in detail in the journal Nature Climate Change.

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