40-Million-Year-Old Asian Monsoon is 'Closely Linked to Global Climate'

Scientists say that the largest climate system in the world, the Asian monsoon that brings seasonal rains to the region is as much a result of global climate as topography.

This suggests that increasing atmospheric CO2 will increase the monsoonal precipitation significantly, as has already been experienced in the recent deluges that have flooded cities in the continent, including the recent Kashmir floods.

The study led by University of Arizona shows that the monsoon, believed to be a more recent phenomenon following the uplift of the Tibetan plateau 22 odd million years ago, is actually as old as 40 million years.

The monsoon pattern began when atmospheric CO2 was three to four times greater than it is now. It then weakened 34 million years ago when atmospheric CO2 decreased by 50% and an ice age occurred.

The team's paper was published online in the journal Nature on September 14.

The discovery was made by three teams looking at various aspects of the environment of 40 million years ago.

Lead author Alexis Licht and team were examining snail and mammal fossils in Myanmar. Another team was studying lake deposits in Xining Basin in central China while the third team created climate simulations of the Asian climate 40 million years ago.

Licht analysed 40-million-year-old freshwater snail shells and teeth of mammals to see what types of oxygen they contained. The ratio of oxygen-18 and oxygen-16 shows whether the animal lived in a relatively wet climate or an arid one. The ratio seen in the fossils showed the region had a seasonal pattern very much like the current monsoon – dry winters and very rainy summers.

The team of researchers working in China found dust deposits dating back to 41 million years, proving monsoon that generates winter winds blowing dust from central Asia to China was in action. The third team's climate simulations indicated strong Asian monsoons 40 million years ago and linked them to atmospheric CO2.