A million years of data confirms it: monsoons are likely to get worse


Global warming is likely to make the monsoon season in India wetter and more dangerous, new research shows.

Scientists have known for years that climate change is disrupting the monsoon season. Previous research based on computer models has suggested that global warming caused by greenhouse gases and increased humidity in the warmed atmosphere would lead to more rainy summer monsoon seasons and precipitation events. unpredictable extremes.

The new article, published Friday in the journal Science Advances, adds evidence for the theory by looking at the past million years to give some idea of ​​the monsoons to come.

The monsoon season, which usually runs from June to September, brings enormous amounts of rain to South Asia which is crucial for the agrarian economy of the region. These rains affect the lives of a fifth of the world’s population, feeding or destroying crops, causing devastating floods, killing people and spreading pollution. Changes brought on by climate change could reshape the region, and history, the new research suggests, is a guide to those changes.

The researchers didn’t have a 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 monsoon season runoff flows from the subcontinent.

The carrots were 200 meters long and provided a rich record of monsoon rainfall. The wetter seasons put more fresh water in the bay, reducing the salinity on the surface. The plankton that lives on the surface die and sink into the sediment below, layer after layer. Working on the carrots, scientists analyzed the fossil shells of plankton, measuring isotopes of oxygen to determine the salinity of the water they lived in. The heavy precipitation and periods of low salinity occurred after periods of higher atmospheric carbon dioxide concentrations, lower levels of global ice volume, and subsequent increases in regional moisture-carrying winds.

Now that human activity is increasing levels of greenhouse gases in the atmosphere, research suggests, we can expect to see the same monsoon patterns emerge.

Steven Clemens, professor of earth, environmental and planetary sciences at Brown University and lead author of the study, said: “We can verify that over the last million years the increase in carbon dioxide in the atmosphere was followed by a substantial increase in precipitation in the South. Asian monsoon system. The predictions of climate models are “wonderfully consistent with what we are seeing over the past million years,” he said.

Anders Levermann, professor of climate system dynamics at the Potsdam Institute in Germany who was not involved in the new paper but produced research on the climate model’s monsoon projections, said he was happy to see research that supported the conclusions of the future – researching climate models. “It’s a huge body of information,” he said, “and it’s really nice to see real data that reflects over a million years of our planet’s history, to see the physical laws that we experience every day leave their mark in this extremely rich paleo-record context.

Dr Levermann added that the consequences for the inhabitants of the Indian subcontinent are dire; the monsoon is already dropping huge amounts of rain and “can still be destructive,” he said, but the risk of “catastrophically strong” seasons is increasing, and the increasingly erratic nature of the seasons has its own risks. “And it hits the biggest democracy on the planet; in many ways the most contested democracy on the planet, ”he said.

Dr Clemens and other researchers collected their samples during a two-month research trip on a converted oil rig ship, the JOIDES Resolution. He carried a crew of 100 and 30 scientists on a trip that began in November 2014. “We were out on Christmas,” he recalls, and although “it was difficult to be away from his family so long ”, the reward has finally arrived. “We’ve been through those years,” he said, “creating these datasets. It’s gratifying to have finally released this.

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