Green roof of City Hall in Chicago, Illinois. Installing green roofs is one of the adaptation measures that cities can use to lower local temperatures and hence the economic impacts of climate change. Photo: Wikimedia Commons, licensed under CC BY-SA 3.0
Green roof of City Hall in Chicago, Illinois. Installing green roofs is one of the adaptation measures that cities can use to lower local temperatures and hence the economic impacts of climate change. Photo: Wikimedia Commons, licensed under CC BY-SA 3.0

Economists generally expect climate change to cost a lot of money and impact nearly every sector of the economy. And now, according to new research published in the journal Nature Climate Change last month, it appears cities could be hit even harder if they don’t take efforts to mitigate the impacts of rising global temperatures.

The higher climate toll that cities will pay is due to the urban heat island effect, which is caused by the replacement of vegetation and bodies of water by concrete, asphalt, and other materials that trap more heat. The effect is only further exacerbated by the abundance of things like cars and air conditioners in urban areas, which emit more heat and global warming pollution.

The US Environmental Protection Agency says that, while there are some positive impacts of the urban heat island effect, such as a longer growing season, most are decidedly negative, such as increased energy consumption, higher rates of air pollution and greenhouse gas emissions, poorer water quality, and associated risks to human health.

All of these impacts can have an obvious effect on a large urban area’s economy, even while the heat island effect makes heat waves worse, leading to lower worker productivity. So it’s perhaps no surprise that, according to the authors of the Nature Climate Change study, “The impacts of [global climate change] in cities are likely to be amplified by those of the [urban heat island effect].”

An international team of researchers with the UK’s University of Sussex, Universidad Nacional Autónoma de México, and Vrije University Amsterdam looked at 1,692 cities around the world in order to determine just how much the urban heat island effect could compound the losses already expected to result from global warming.

First, they quantified just how much the urban heat island effect will magnify increasing average temperatures in cities due to global warming. “For the most populated cities (that is, the top 5%), the effects of [urban heat islands] add 1.72°C, 2.08°C and 2.35°C to the temperature increase due to [global climate change] in 2015, 2050 and 2100, respectively,” the researchers note in the report.

“These estimates are 0.70°C, 0.84°C and 0.93°C for the median cities. About 20% of these cities could experience a total warming higher than 4°C in 2050 and about 25% could warm more than 7°C by the end of this century.”

The researchers found that, on average, economic losses from higher temperatures could be 2.6 times higher in cities than they would be if heat island effects weren’t factored into the equation.

Some cities, of course, will fare worse than others. The hardest hit, per the report, could lose as much as 10.9% of their gross domestic product (GDP) by 2100 due to the combined effects of climate change and the heat island effect, far higher than the global average of 5.6%.

But even under the lowest emissions scenarios, the costs to cities could be as much as 30% higher than they would be without heat island effects. What this shows, according to Richard SJ Tol, a professor of Economics at the University of Sussex, is that “any hard-won victories over climate change on a global scale could be wiped out by the effects of uncontrolled urban heat islands.”

If the study contains any good news, it’s that local economic impacts can be tempered by adaptation policies at the city level. Cool pavements, green roofs, and expanding vegetation in cities are among the tactics for mitigating warming that the researchers examined for the study.

The most cost-effective measure, according to their models, is moderate-scale installation of cool pavements and roofs, which reflect more sunlight and thus absorb less heat. Cities can reduce air temperatures by about 0.8 degrees by changing 20% of their roofs and half of their pavement to “cool” materials, thus saving up to 12 times as much money as it would cost to install and maintain those cool roofs and paved areas.

The benefits of these local efforts are amplified when done in concert with effective global efforts to mitigate global warming, Tol adds. “It is clear that we have until now underestimated the dramatic impact that local policies could make in reducing urban warming,” he said in a statement.

“However, this doesn’t have to be an either/or scenario. In fact, the largest benefits for reducing the impacts of climate change are attained when both global and local measures are implemented together. And even when global efforts fail, we show that local policies can still have a positive impact, making them at least a useful insurance for bad climate outcomes on the international stage.”

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The article first appeared on Mongabay. Read it here.

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