Summers around the world are already warmer than they used to be, and they’re going to get dramatically hotter by century’s end if carbon pollution continues to rise. That problem will be felt most acutely in cities. The world’s rapidly growing population coupled with the urban heat island effect — which can make cities up to 14°F (7.8°C) warmer than their leafy, rural counterparts — add up to a recipe for dangerous and potentially deadly heat. Currently, about 54 percent of the world’s population lives in cities, and by 2050 the urban population is expected to grow by 2.5 billion people. As those cities get hotter, weather patterns may shift and make extreme heat even more common. That will in turn threaten public health and the economy.
Under the high-pollution scenario, currently mild Ottawa, Canada could have the tropical climate of Belize City by 2100. The average land temperature is projected to rise 8.6°F (4.8°C), but due to the vagaries of geography, some cities will warm much more. Sofia, Bulgaria has the biggest overall temperature shift, with temperatures rising nearly 15°F (8.4°C) by 2100. Up to a dozen cities will heat up so much, their summers will have no analog currently on Earth. Reducing carbon emissions still means temperatures will rise in cities (and everywhere else). Dealing with less extreme heat makes adaptation easier and less expensive, and given that choice, perhaps it’s no surprise cities are leading the charge on climate change. They face the worst impacts of extreme heat and are home to billions. That’s why thousands of mayors from around the world have banded together and pledged to reduce their emissions.
That includes multitudes of U.S. cities committing to meet the Paris Agreement goals after President Trump announced he was pulling the U.S. from the pact, and even more ambitious moves like Oslo’s pledge to nearly zero its emissions by 2030.
Kemo D. 7