A million years of data confirms: Monsoons are likely to get wetter and more dangerous

John Schwartz writes:
Last Updated: Jun 05, 2021, 04:10 PM IST

Global warming is likely to make India’s monsoon season wetter and more dangerous, new research suggests.

Scientists have known for years that climate change is disrupting monsoon season. Past research based on computer models has suggested that the global heating caused by greenhouse gases, and the increased moisture in the warmed atmosphere, will result in rainier summer monsoon seasons and unpredictable, extreme rainfall events.

The new paper, published Friday in the journal Science Advances, adds evidence for the theory by looking back over the past million years to give a sense of monsoons to come.

The monsoon season, which generally runs from June to September, brings enormous amounts of rain to South Asia that are crucial to the region’s agrarian economy. Climate change could reshape the region, and history, the new research suggests, is a guide to those changes.

The researchers had no time machine, so they used the next best thing: mud. They drilled core samples in the Bay of Bengal, in the northern Indian Ocean, where the runoff from monsoon seasons drains away from the subcontinent.

The core samples were 200 meters long and provided a rich record of monsoon rainfall. Wetter seasons put more fresh water into the bay, reducing the salinity at the surface. The plankton that live at the surface die and sink to the sediment below, layer after layer. Working through the core samples, the scientists analyzed the fossil shells of the plankton, measuring oxygen isotopes to determine the salinity of the water they lived in. The high-rainfall and low-salinity times came after periods of higher concentrations of atmospheric carbon dioxide, lower levels of global ice volume and subsequent increases in regional moisture-bearing winds.

Now that human activity is boosting levels of atmospheric greenhouse gases, we can expect to see the same monsoon patterns emerge.

Anders Levermann, a professor of climate dynamics at the Potsdam Institute in Germany who was not involved in the new paper, said that he was pleased to see research that supported the findings of forward-looking climate models. “It’s a tremendous body of information,” he said, “and it’s really nice to see in actual data that reflects more than a million years of our planet’s history, to see the physical laws that we experience every day leave their footprints in this extremely rich paleo-record.”
Courtesy: The New York Times