Catherine Yang

A new Yale study suggests there will be no abrupt shift in monsoon strength in the next century despite climbing levels of aerosol emissions and greenhouse gases.

The study reports that the “tipping-point” theory, the basis previous studies have used to claim that monsoons will suddenly cease due to climate change, is incorrect. Corrected data found that the responses of monsoons to human-induced climate changes — otherwise known as anthropogenic forcings — are linear, suggesting that abrupt change in monsoon behavior would be unlikely.

“There were two studies previously published in [Proceedings of the National Academy of Sciences] … that stated that monsoons could shut down abruptly — within a single year — in response to human-induced changes in the environment,” geology and geophysics professor William Boos, a study co-author, said. “Our paper showed that the theory on which that previous work was based is wrong.”

Monsoons are continental-scale patterns of winds that bring rainfall to the tropics during the summer season, sustaining billions of lives in parts of Asia, Africa and the Americas. An abrupt shutdown of monsoons would mean a hot and dry climate year-round in regions that depend on a wet season, Boos added.

Previous studies have relied on the tipping-point theory to argue that if human-induced and natural environmental change reaches a certain threshold, monsoon strength would abruptly decrease. According to the study, this theory ignores the fact that air cools as it rises. But the corrected theory reveals that natural changes will not significantly alter the strength or volume of monsoons for at least a century, Boos said.

“Although monsoons are expected to change in response to anthropogenic forcings, there is no reason to expect an abrupt shift into a dry regime in the next century or two,” the study reads.

Anthropogenic forcing describes the ways in which humans have altered the energy of a system, such as changes in greenhouse-gas concentrations, aerosol emissions and properties of land surfaces.

While monsoons may not cease entirely, the study still claims that anthropogenic factors will impact the strength of monsoons over the years.

“We found quite a strong response of monsoons to changes in greenhouse-gas concentrations and to changes in land-surface properties,” Boos said. “Normal year-to-year variability in monsoons will be superimposed on this, so there will be occasional droughts and floods, and such extreme events may even become worse over time.”

Geology and geophysics professor Trude Storelvmo, a study co-author, emphasized that their study did predict “substantial” changes to monsoons but that these changes would be more gradual than abrupt.

The study’s linear model supports the idea that there will not be abrupt nonlinear shifts in seasonal monsoons based on anthropogenic factors, Boos added.

“Previous studies have indicated that monsoons could go through abrupt transitions once a critical amount of atmospheric particles, greenhouse gases or land-cover changes were reached, with obvious implications for the millions of people whose livelihood depend on monsoon rain,” Storelvmo said. “Our results show no evidence of such abrupt changes.”

The study was published in Proceedings of the National Academy of Sciences on Jan. 25.