Imagine Montreal in July going from 32C to 40C.
The median city stands to lose between 1.4 and 1.7% of GDP per year by 2050 due to climate change. Photograph: Anadolu Agency/Getty Images
Under a dual onslaught of global warming and localised urban heating, some of the world’s cities may be as much as 8C (14.4F) warmer by 2100, researchers have warned.
Such a temperature spike would have dire consequences for the health of city-dwellers, rob companies and industries of able workers, and put pressure on already strained natural resources such as water.
The projection is based on the worst-case scenario assumption that emissions of greenhouse gases continue to rise throughout the 21st century.
The top quarter of most populated cities, in this scenario, could see temperatures rise 7C or more by century’s end, said a study in the journal Nature Climate Change.
For some nearly 5C of the total would be attributed to average global warming.
The rest would be due to the so-called “urban heat island” effect, which occurs when parks, dams and lakes, which have a cooling effect, are replaced by concrete and asphalt – making cities warmer than their surrounds, the researchers said.