‘Heat Islands’ Double the Cost of Climate Change in the World’s Largest Cities

The built environment, whether concrete structures or paved roads, absorbs heat, increasing the impact of global warming — but alternative materials could be a relatively cheap way to reduce temperature rise.

An international team of economists has found that large cities may shoulder a disproportionate burden from climate change due to the amplifying effect of urban heat islands. While warming cities will bring big energy costs, researchers say they may also offer important insight into the role of local policy in climate change mitigation.

In a study published today in Nature Climate Change, researchers in Mexico, the Netherlands, and the United Kingdom analyzed nearly 1,700 cities around the world. When the urban heat island effect was taken into account, they found that the economic cost of climate change for these cities would be 2.6 times higher than previously thought.

“Any hard-won victories over climate change on a global scale could be wiped out by the effects of uncontrolled urban heat islands,” Richard Tol, a professor of economics at the University of Sussex and one of the authors on the study, said in a statement.

Urban heat islands are the result of replacing the natural landscape, such as vegetation and waterways, with heat-absorbing materials like concrete or asphalt. It is a common problem in large cities and one that is further compounded by the heat emitted from a high concentration of vehicles and air conditioning units.

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The process is known to have severe local impacts, altering the local energy balance and causing changes to local weather, including wind patterns and precipitation.

The study authors emphasize that this effect could extend to potentially “devastating” economic consequences for cities that will need to pay more to cool buildings, clean polluted air, and ensure clean drinking water. Worker productivity in such environments is also expected to drop and health costs are expected to jump.

In the worst hit cities, the economists estimate, the losses could reach 10.9 percent of GDP by the end of the century, double the expected global average loss of 5.6 percent.

And urban heat islands will amplify already increasing temperatures. In 2016, global temperatures were the warmest since records were first kept in 1880, according to NASA and NOAA. While temperatures are expected to keep rising, the study authors expect that by 2050, the phenomenon will add an additional two degrees Celsius to temperatures for the most populated cities.

Although large cities cover roughly one percent of the Earth’s surface, they consume 78 percent of the world’s energy and contain more than half of the world’s population. While most climate change studies have focused on sea level rise and water resources, the authors say research has ignored the aggravated impact such changes will have on large cities. In doing so, they believe the potential of city-level policy to play a leading role in climate change mitigation has also been overlooked.

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The researchers found that the installation of cool pavement, which absorbs less heat, together with the installation of green roofs and an expansion of vegetation in cities are the most promising methods for combining heat islands. Cool pavement and roofs proved to be the most cost-efficient policies to implement.

According to the authors, changing 20 percent of the city’s roofs and half of its pavement to cool forms would save up to 12 times the cost of installation and maintenance. And they could reduce air temperatures by 0.8 degrees Celsius.

“It is good to get economic numbers on the likely effect of urban heat island mitigation,” said Rohinton Emmanuel, a professor of sustainable design at Glasgow Caledonian University who works on the impacts of urban heat islands.

He lauded the authors on their work while noting that such a large-scale analysis would be inevitably “crude.” Some of the strategies proposed by authors, such as improving the “urban albedo” — or a city’s reflectivity —could have unintended consequences such as glare, he noted.

But he, like the authors of the study, is optimistic that such data will help policymakers to understand the importance of local policies to mitigate urban heat islands and larger patterns of climate change.

“Even when global efforts fail, we show that local policies can still have a positive impact,” Tol said in the statement, “making them at least a useful insurance for bad climate outcomes on the international stage.”

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This may come as some consolation on the heels of the G7 Summit in Taormina, Italy last week. While six world leaders reiterated their commitment to the Paris accord, US President Trump hedged, saying that the United States – by far the biggest polluter in the G7 – would announce a decision this week.

In the meantime, the authors urge local policy makers to start acting. “The largest benefits for reducing the impacts of climate change,” they wrote, “are attained when both global and local measures are implemented together.”

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