Cities’ Heat Changing Weather

The heat emanating from cities affects the weather patterns of areas thousands of miles away, according to a recent study in Nature Climate Change. The study is the first to demonstrate the far-reaching effects of waste heat from cities and to explain the rise in winter warming patterns across North America and northern Asia.

Waste heat in cities comes from everything that burns energy—from power plant smokestacks to car tailpipes—and, according to the study, alters the flow of the jet stream, impacting weather patterns across an entire region. This impact has led to these warmer winters—about a degree over what climate models predicted—in North American and northern Asia in recent decades.

“Nobody has seen … such a far-reaching impact,” said Aixue Hu, an atmospheric scientist at the National Center for Atmospheric Research and a co-author of the study.

Cities appear to have this major impact because they tend to be located on coasts, where ridges from high pressure and troughs of low pressure form and impact jet streams. While certain regions experience additional warmth, the altering of these jet streams makes it cooler elsewhere—particularly Northern Europe during the summer and autumn months.

“Waste heat does not really contribute to global mean temperature change,” Hu said. “But it does affect regional climate.”

And this waste heat differs from what is known as the urban heat island effect in which urban areas, due to the vast amount of pavement and buildings and lack of vegetation, have higher temperatures than surrounding areas, particularly during the day.

According to the researchers, about 40% of the world’s energy consumption comes from just 86 metropolitan in the Northern Hemisphere. They note that, in the future, computer models will need to take waste heat into account in making weather-related predictions.