January 28th, 2013 by James Ayre
Large cities have been found to have a significant effect on the weather, even for thousands of miles around the urban area, new research from the Scripps Institution of Oceanography; University of California, San Diego; Florida State University; and the National Center for Atmospheric Research, has found.
The new research shows the enormous effect that human activities are having on the behavior of certain aspects of the atmosphere, especially the jet stream. “The heat generated by everyday activities in metropolitan areas alters the character of the jet stream and other major atmospheric systems. This affects temperatures across thousands of miles, significantly warming some areas and cooling others.”
This ‘waste heat’ that is generated by the buildings, cars, and the other infrastructure present in major Northern Hemisphere urban areas causes changes in the behavior of the jet stream, leading to more winter warming in some regions, and less in others, than predicted by models. It has a very negligible effect on overall global temperature though. In short, affecting the weather, not the climate.
“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 percent of the heat transported across higher latitudes by atmospheric and oceanic circulations.”
The study found that large swaths of northern North America and northern Asia have experienced temperature increases of as much as much as 1 degree Celsius (1.8 degrees Fahrenheit) because of this effect.
The researchers say that this helps to explain why some regions have so far experienced more warming than predicted, and others less. (Global temperatures have been continuing to rise.)
“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 NCAR scientist Aixue Hu, the coauthor of the study. “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 researchers make a point to distinguish between this waste heat, and the ‘urban heat island effect’. This effect is caused by actual heat being released through heating and cooling activities, transportation, and industrial activity; the ‘urban heat island effect’ is simply the effect of materials such as asphalt absorbing heat from the Sun and then remitting it.
The research was done by analyzing “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 (1 terawatt, or TW, equals 1 trillion watts). Of that, an average rate of 6.7 TW was consumed in 86 metropolitan areas in the Northern Hemisphere.”
They then used a computer model to explore the effects that this heat has on the atmosphere, finding that it may 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,” Zhang says. “This is accomplished through atmospheric circulation change.”
“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,” Cai says. “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.”
The new research was just published this week in the journal Nature Climate Change.
Image Credits: NASA and NOAA;
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