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Study finds urban waste heat affects temperatures across thousands of miles, warming some areas and cooling others
28 January 2013
The waste heat generated by everyday activities in metropolitan areas—which is distinct from the urban heat island effect—alters the character of the jet stream and other major atmospheric systems, affecting temperatures across thousands of miles, significantly warming some areas and cooling others, according to a new study published in the journal Nature Climate Change.
The extra waste heat generated from buildings, cars, and other sources in major Northern Hemisphere urban areas causes winter warming across large areas of northern North American and northern Asia. Temperatures in some remote areas increase by as much as 1 degree Celsius (1.8 degrees Fahrenheit), according to the research by scientists at the Scripps Institution of Oceanography, University of California, San Diego; Florida State University; and the National Center for Atmospheric Research.
At the same time, the changes to atmospheric circulation caused by the waste heat cool areas of Europe by as much as 1 degree C (1.8 degrees F), with much of the temperature decrease occurring in the fall.
The results show that the inclusion of energy use at 86 model grid points where it exceeds 0.4 W m−2 can lead to remote surface temperature changes by as much as 1 K in mid- and high-latitudes in winter and autumn over North America and Eurasia. These regions correspond well to areas with large differences in surface temperature trends between observations and global warming simulations forced by all natural and anthropogenic forcings. We conclude that energy consumption is probably a missing forcing for the additional winter warming trends in observations.—Zhang et al.
The net effect on global mean temperatures is nearly negligible—an average increase worldwide of just 0.01 degrees C (about 0.02 degrees F). This is because the total human-produced waste heat is only about 0.3% of the heat transported across higher latitudes by atmospheric and oceanic circulations.
However, the noticeable impact on regional temperatures may explain why some regions are experiencing more winter warming than projected by climate computer models, the researchers conclude. They suggest that models be adjusted to take the influence 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. 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.—NCAR scientist Aixue Hu, a co-author of the study
The researchers stressed that the effect of waste heat is distinct from the so-called urban heat island effect. Such islands are mainly a function of the heat collected and re-radiated by pavement, buildings, and other urban features, whereas the new study examines the heat produced directly through transportation, heating and cooling units, and other activities.
The study was funded by the National Science Foundation, NCAR’s sponsor, as well as the Department of Energy and the National Oceanic and Atmospheric Administration.
Hu, along with lead author Guang Zhang of Scripps and Ming Cai of Florida State University, analyzed the energy consumption—from heating buildings to powering vehicles—that generates waste heat release. The world’s total energy consumption in 2006 was equivalent to a constant-use rate of 16 terawatts (TW); of that, an average rate of 6.7 TW was consumed in 86 metropolitan areas in the Northern Hemisphere.
Using a computer model of the atmosphere, the authors found 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. This is accomplished through atmospheric circulation change.—Guang Zhang
The release of waste heat is different from energy that is naturally distributed in the atmosphere, the researchers noted. The largest source of heat, solar energy, warms Earth’s surface and atmospheric circulations redistribute that energy from one region to another. Human energy consumption distributes energy that had lain dormant and sequestered for millions of years, mostly in the form of oil or coal.
Though the amount of human-generated energy is a small portion of that transported by nature, it is highly concentrated in urban areas. In the Northern Hemisphere, many of those urban areas lie directly under major atmospheric troughs and jet streams.
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. 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.—Ming Cai
The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Guang J. Zhang, Ming Cai & Aixue Hu (2013) Energy consumption and the unexplained winter warming over northern Asia and North America. Nature Climate Change doi: 10.1038/nclimate1803
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