The history of a monsoon-inducing plateau
Towering 4.8 km above sea level, the Tibetan Plateau covers 2.5 million km2 of mountains and deserts. By virtue of its height and thermal mass, the plateau warms the upper atmosphere, which leads to global circulation patterns that cause the East Asian monsoon. But the Tibetan Plateau wasn’t always a prominent feature on Earth, and climatologists have wondered whether the monsoons developed at the same time as the plateau’s uplift. New research shows that the evolution of Asia’s climate depended on not only the plateau’s height but also its latitudinal position relative to today.
Geologists believe that the proto-Tibetan Plateau began to rise in the tropics, more than 1000 km south of its current position, as the Indian and Asian continental plates collided 60 million–40 million years ago. Ran Zhang from the Chinese Academy of Sciences and his colleagues ran climate simulations to compare the difference in wind and precipitation patterns surrounding a plateau that formed in the tropics versus one that uplifted in its modern-day position, as was assumed in previous paleoclimate studies. The simulations showed that if the plateau migrated northward, the Asian paleoclimate would have lacked the key features of a modern monsoon climate: intense precipitation over East Asia and inland aridity in northwestern China. If the Tibetan Plateau formed at its current position, the East Asian climate would have developed more rapidly in response to the plateau’s uplift. By varying uplift rate and latitude, the researchers showed that even a plateau of modest elevation profoundly influenced when and where precipitation patterns developed.
Examining the relationship among the Tibetan Plateau’s latitude, elevation, and climate provides an important step toward reconstructing Asia’s climate history. It offers a new constraint for testing theories about how other factors, such as global temperature changes and vegetation, affected ancient conditions. (R. Zhang et al., Earth Planet. Sci. Lett. 484, 295, 2018 .)
