Increased vegetation in China and India is altering large-scale atmospheric currents, cooling western Eurasia and warming northern North America, according to researchers at Nanjing University of Information Science and Technology.
The findings, published in the journal Advances in Atmospheric Sciences, show that simultaneous greening in both Asian nations triggers planetary atmospheric shifts despite the vast distances separating them from other continents.
Scientists analysed satellite data spanning from 1982 to 2020 and simulated atmospheric changes using the CAM6.0-CLM5.0 land-atmosphere model. China and India together account for nearly one third of the global increase in vegetation cover observed in recent decades.
A single tree planted in China will not cool Europe by itself across thousands of kilometres. However, when large expanses of land grow greener, plants release more water into the air, affecting cloud formation and creating an uneven distribution of heat that alters major planetary air currents.
Contrasting climate impact in China and India
The computer simulations revealed notable differences between the two Asian nations. In China, increased plant cover leads to a general drop in temperatures along with higher rainfall in the southern and northeastern regions of the country.
In India, the trend is reversed, with temperatures rising while precipitation decreases across widespread areas.
Miao Yu, an author of the study, explained that adopting ecological practices does not necessarily produce the same climate response everywhere. The disparity stems from how moisture released by plants behaves in each region.
In southern China, added atmospheric moisture fuels cloud formation that blocks solar energy and cools the surface. In India, that same moisture dissipates into fewer clouds, allowing more solar energy to reach the ground and raising temperatures despite the growth in vegetation.
Nanjing University of Information Science and Technology, located in Jiangsu province, China, is a public university recognized for its atmospheric science and meteorological research. Land-atmosphere models like CAM6.0-CLM5.0 simulate complex interactions between land surface processes, vegetation dynamics, and global weather patterns.
Disrupting Asian jet streams and Rossby waves
When China and India experience greening at the same time, regional atmospheric processes interact to alter the jet streams over Asia. This interaction modifies the propagation of Rossby waves, which are giant atmospheric waves capable of transmitting climate influences across vast distances.
Across Eurasia, these atmospheric adjustments favor the entry of cold polar air, resulting in a cooling effect over the western portion of the continent. Conversely, at the opposite side of the Northern Hemisphere in northern North America, warming remains the dominant outcome.
Min Xiao, the lead author of the study, said the atmosphere connects regions that appear far apart. Xiao added that changes in vegetation in one region can amplify, weaken, or even reverse climate effects observed in another area.
Rossby waves, also known as planetary waves, are natural meanders in high-altitude atmospheric winds driven by Earth's rotation and temperature variations between polar and equatorial regions. Jet streams are fast-flowing air currents in the upper atmosphere that direct weather systems across continents, meaning modifications to their paths can shift weather patterns thousands of miles away.
Reforestation policies and future climate modeling
The study highlights major implications for large-scale reforestation and environmental restoration projects. While expanding plant cover absorbs atmospheric carbon dioxide, plants also alter the exchange of water and energy with the atmosphere, giving larger greened land areas a broader climate reach.
The authors cautioned that their conclusions are based on simulations from a single land-atmosphere model. They noted that both the cooling in Eurasia and the warming in North America will need to be confirmed through further research using additional climate models.
