Asian Monsoon May be Far Older Than Previously Thought: 40 Million Years in the Past

The Asian monsoon occurs each year, bringing with it torrential summer rains and dry winters. Now, scientists have taken a closer look at this climate phenomenon and have found that it existed as early as 40 million years ago, which makes it far older than previously thought.

Previously, researchers believed that the climate pattern known as the Asian monsoon began between 22 and 25 million years ago as the result of the uplift of the Tibetan Plateau and the Himalaya Mountains. This climate pattern, the largest system in the world, actually governs the conditions in much of mainland Asia today.

In order to find out a bit more about the origins of the monsoon, the researchers combined different lines of evidence from different locations. One team examined snail and mussel fossils in Myanmar. By looking at the types of oxygen they contained and the ratio of two different forms of oxygen, the researchers could tell whether the animals lived in a relatively wet climate or an arid one. In addition, the scientists created climate simulations of the Asian climate about 40 million years ago.

"One of the goals of the study was to document the pre-monsoonal conditions, but what we found were monsoonal conditions," said Alexis Licht, lead author of the new study, in a news release. "The early primates of Myanmar lived under intense seasonal stress-aridity and the monsoons. That was completely unexpected."

The researchers found evidence supporting the existence of the monsoon about 40 million years ago. Because the monsoon climate pattern generates winter winds that blow dust from central Asia and deposit it in thick piles in China, the scientists could use evidence of these deposits as evidence of the monsoon.

"This finding has major consequences for the ongoing global warming," said Licht. "It suggests increasing the atmospheric CO2 will increase the monsoonal precipitation significantly."

The findings reveal a bit more about the past climate in the region, and also pave the way for future climate research. Currently, the scientists plant to investigate how geologically short-term increases of atmospheric CO2 known as hyperthermals affected the monsoon's behavior 40 million years ago.