Climate change: cities are warming faster than countries

On a global average, and over a longer period of time, inner cities are warming 29 percent faster than neighboring rural areas. This is the result of an assessment of satellite measurements of the surface temperatures of more than 2,000 cities and corresponding comparison areas from 2002 to 2021. The analysis in the specialist journal Earth and Environmental Communications also shows that urban green spaces can reduce temperature increase.

urbanization in asia

“Little is known about how surface warming trends in global cities differ from those characterized by weather observations in remote rural areas,” wrote the team, led by Wenfeng Zhan of Nanjing University in China. Against the background of rapid urbanization in many Asian countries, they also considered areas that developed from rural to urban areas during the observation period. So Zhan and colleagues divided the regions into urban, rural, and transitional.

0.56 more points per decade

As a global average, scientists have identified an increase in daily temperature in inner cities of 0.56°C per decade. In rural areas, the comparative value was only 0.40°. At night, the difference is not entirely at 0.43 degrees (city) and 0.37 degrees (state). However, warming was strongest in the transitional regions: 1.06 degrees during the day and 0.84 degrees at night over a decade.

According to the researchers, the warming of cities is partly due to climate change, which is causing an increase in global average temperatures. On the other hand, the expansion and condensation of cities also contribute to this.

The bigger the city, the warmer it is

Analysis according to city size showed that the higher the temperature of the inner city, the larger the city. Small cities of less than 65 square kilometers only show a daily increase in temperature of 0.41 degrees per decade. For cities of more than 450 square kilometers it is 0.69 degrees. From the perspective of the continent, cities in Asia have a value of 0.71 degrees during the day, while it is only 0.44 degrees in Europe.

The researchers were able to show that warming in a city eases if there are many plants and green spaces there. In conclusion, they wrote: “Our results confirm that urban greening is an effective strategy for mitigating surface warming in urban areas.”