Urban Heat Causes A Different Kind of Climate Change

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Cities are changing the climate across continents. Photo: Cranestation / CC by 2.0

A city’s influence can extend far beyond the city itself. Image by Cranestation (CC 2.0)

Urban Heat Causes Temperature Changes Across Continents

The thing about heat is that it is not a linear, up and down phenomenon. Air moves, and it moves across the landscape on a huge scale. Like a warm vent in the ocean, cities have become warm hubs on the landscape, sending out heat into the atmosphere around them. They heat up the lower atmosphere, and this heat rises to impact the upper atmosphere, ultimately impacting the jet stream. This means that an urban area can change heat distribution across continents, altering the way that climate changes.

Changing Our Neighbors’ Climate

The study also revealed an interesting geographic dispersal of climate change. The changes related to the jet stream tend to have a west to east gradient. Because of urban heat emissions, temperatures have changed across continents. Across the North American and Eurasian continents, areas in the west are cooler, while areas in the east are warmer. This means that urban-induced changes in the jet stream have a cooling effect on the Pacific coast of North America and in the Atlantic regions of Europe, as the opposite side of the continent warms.

Modifying the Climate Impacts of Urban Heat Emissions

Interestingly, the cure for this sort of climate change is not all about modifying greenhouse gas emissions. Instead, it’s about changing the way in which people use energy. When many people use energy, they emit a lot of heat, and it doesn’t really matter how that energy is produced. What does matter is the amount of energy used. Hu told Decoded Science, “If we keep the lifestyle we have, no matter whether we burn fossil fuels or renewables, when we increase our consumption of energy we will increase this effect.”

The solution to hot cities is to modify heat emissions. If people insulate their homes and use less energy, emitting less to the environment around them, it will result in cooler cities and a lower impact on the surrounding climate.

Local Impacts Are Important

Climate change has innumerable impacts, and changes in global mean temperatures are certainly significant to climate patterns around the world. However, Hu noted that, although global mean temperatures are important, “It’s very important to consider smaller variations in the atmosphere, because we don’t live in the global mean temperature, we live locally.”

In an era of fear about rising greenhouse gas emissions and the upward movement of the global mean temperature, this study highlights the need to look at the details.  Human activities alter the climate in any number of ways, and greenhouse gas emissions are just one of them.

References

Zhang, G.J., Cai, M., and Hu, A. Energy consumption and the unexplained winter warming over northern Asia and North America. (2013). Nature Climate Change. doi:10.1038/nclimate1803. Accessed February 5, 2013.

U.S. Environmental Protection Agency. Causes of Climate Change. (2013). Accessed February 5, 2013.

Oke, T.R. The Energetic Basis of the Urban Heat Island Effect. (2006). Quarterly Journal of the Royal Meteorological Society. doi: 10.1002/qj.49710845502. Accessed February 5, 2013.

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