In China and India, the study estimates that urban expansion was responsible for over 0.23 degrees Celsius of the observed surface warming in cities per decade. (Photo: AFP)
BEIJING: Cities worldwide are warming by 0.5 degrees Celsius on average per decade, 29 per cent faster than in rural areas, according to a study which suggests that climate change and urban expansion are accelerating surface temperatures.
Researchers from Nanjing University in China and colleagues noted that planting trees and vegetation in cities -- also known as urban greening -- is reported to offset about 0.13 degrees Celsius of surface warming per decade in European cities.
People who live in cities experience greater heat exposure during heat wave events than the general population due to the urban heat island effect, in which urban land gets hotter than surrounding rural land, they said.
Climate change and population growth in cities are projected to increase the surface urban heat island effect, but many current estimates of future human heat exposure assume equal rates of surface temperature increase between urban and rural areas, the researchers said.
In China and India, they estimated that urban expansion was responsible for over 0.23 degrees Celsius of the observed surface warming in cities per decade.
Urban greening is suggested to reduce surface warming, but whether it can slow the accelerating surface urban heat island effect remains unclear, the researchers said.
The study, published recently in the journal Communications Earth & Environment, analysed satellite land surface temperature data for over 2,000 city centers worldwide between 2002 and 2021 and compared them to background rural surface temperatures.
Very large "megacities" such as Abujia in Nigeria, Phoenix in the US, London in the UK, Sao Paulo in Brazil, Beijing in China, and Moscow in Russia were included in the analyses.
The study estimates that cities are warming 29 per cent faster than rural areas, and that megacities are warming even more quickly.
The researchers estimated that climate change is the largest contributor to urban surface warming, increasing land surface temperatures by 0.30 degrees Celsius per decade, on average.
However, the researchers also found that urban greening in European cities offset 0.13 degrees Celsius of surface warming per decade, indicating the potential of urban vegetation to slow down surface warming in cities.
For example, increased urban greening in Chicago, US was found to decrease the rate of surface warming by about 0.084 degrees Celsius per decade, they added.