‘Urbanisation’s influence on climate change increasing in recent decades’

NEW DELHI: Urbanisation had contributed to continental-scale warming in recent decades, particularly in Asia where cities have expanded significantly, a new study has revealed. While urbanisation accounts for only 2% of land warming from 1992-2019, researchers advocate for including it in climate change projections. Globally, urban land has increased by 4.5 lakh square kilometers, with the largest growth in Asia and Africa. Some regions, like Europe and the Caribbean, saw dramatic urban area increases, while others, like Iceland and Greenland, remained stable.
Globally, urbanisation has increasingly contributed to warming on the continental scale in the recent decades, especially in rapidly growing regions and countries in Asia, a new research has found. Analysing land temperatures from around the world, researchers found that urbanisation is, however, still not the main cause of climate change, accounting for only two per cent of land warming during the study period of 1992-2019. Urban areas in India were found to have grown by more than 350 per cent.
The researchers, Tirthankar C Chakraborty and Yun Qian, Pacific Northwest National Laboratory, US, said that because cities historically took up a small portion of the Earth’s surface, urbanisation is usually ignored when studying the past and projecting future climate for large regions.
In the study, published in the journal One Earth, the authors argued for including urbanisation, in line with land use changes, in making projections for the future in the climate change scenario, be it local or continental scale.
Using satellite observations, the researchers found that globally, close to 4.5 lakh square kilometres of urban land was added between 1992 and 2019.
Continent-wise, the largest increases came from Asia (312 per cent) and Africa (251 per cent), while the lowest came from Oceania and other islands (155 per cent), they said.
At the country level, over the same period, the Netherlands in Europe and Aruba in the Caribbean showed a more than 1,500 per cent increase, while Iceland and Greenland showed virtually no change, the authors said.
In countries with populations over 20 crore, the researchers found that China, the US and Brazil witnessed a growth in urban area by more than 400 per cent, 180 per cent and 200 per cent.
The growth in urban areas worldwide — from 0.26 per cent to 0.6 per cent — is more than that for the 100 years before that, they said.
Therefore, as the world urbanises and its influence on climate change is increasing, even as it was negligible in the 2000s, they said.
For the highly urbanised Shanghai metropolitan region in China, the researchers found that between 2003-2019, the daytime temperatures rose by 0.4 degrees Celsius per decade, while the nighttime temperatures rose by 0.48 degrees Celsius per decade.
Europe was found to show the strongest daytime land surface temperature trends, which the authors said may partly be due to strong solar brightening during this period. Solar brightening refers to an increase in radiation reaching the Earth’s surface.
On the contrary, China and India, which have experienced significant urbanisation and, thus, strong trends in urban land surface temperatures, showed little changes in their overall land surface temperatures, which the researchers said could partly be due to greening trends during the period 2003-2019.

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