North America’s cities are, quite literally, helping to “pave the way” for the warmer winters that the United States and Canada have been experiencing recently, according to the findings of a new study.
In a paper just published in the journal, Nature Climate Change, “Energy consumption and winter warming,” researchers contend that the “urban heat island effect”—an accepted phenomenon in the scientific community—is partially responsible for the somewhat milder weather that North Americans have experienced for several years.
What is the urban heat island effect? Anyone who lives near a city has noticed that the heat seems to radiate off the concrete and asphalt surfaces at night—making the metropolitan area at least several degrees warmer than the surrounding suburbs and rural regions. The reason is that urban paving and building materials are good conductors of heat. They absorb the heat during the daytime—leaving the surface and the air above the sidewalks, streets, and buildings a little cooler. At night, however, the heat is conducted upward and released in and around the city.
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And now, the scientists say, when ambient city heat–which is a few degrees higher than it was prior to global warming— is picked up by the jet stream currents in the air, it can lead to massive changes over a large area—causing temperatures to rise or fall by nearly two degrees Fahrenheit thousands of miles away. Winter warming was detected as far away from cities as the Canadian prairies.
The climatologists—Guang J. Zhang of Scripps Institution of Oceanography; Ming Cai of the Department of Earth, Ocean, and Atmospheric Science–Florida State University; and Aixue Hu of the National Center of Atmospheric Research— found a similar pattern in Asia, where major population centers conducted heat throughout Russia, northern Asia, and eastern China.
“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,” lead author Guang Zhang was quoted in Smithsonian Magazine. “This is accomplished through atmospheric circulation change.”
The overall effect of this trend on the climate, the researchers say, is negligible: It is easily dwarfed by the effect of greenhouse gases in trapping heat and causing long-term climate change. It does, however, account for various anomalies in the difference between warming predicted by computer models and what’s actually been observed. Future models will need to take into account this phenomenon as they attempt to simulate the impact of climate change in various areas.
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Edited by Brooke Neuman