Global warming is likely to make India’s monsoon season more humid and dangerous, new research suggests.
Scientists have known for years that climate change disrupts the monsoon season. Previous research based on computer models has shown that global warming caused by greenhouse gases and the increased humidity in the warmed atmosphere will result in more rainy summer monsoons and unpredictable extreme rainfall.
The new paper, published Friday in Science Advances magazine, adds evidence to support the theory by looking back over the last million years to give a sense of the monsoons to come.
The monsoon season, which usually lasts from June to September, brings enormous amounts of rain to South Asia, which is vital to the region’s agriculture. These rains affect the lives of a fifth of the world’s population, feed or destroy crops, cause devastating floods, claim human lives and spread pollution. The changes caused by climate change could reshape the region, and history, new research says, 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 the monsoon runoff drains from the subcontinent.
The core samples were 200 meters long and provided a rich record of monsoons. Weather seasons bring more fresh water into the bay and reduce the salinity on the surface. The plankton living on the surface dies and sinks layer by layer into the underlying sediment. Using the drill core samples, the scientists analyzed the fossil shells of the plankton and measured oxygen isotopes to determine the salinity of the water in which they lived. The periods of high precipitation and low salinity came after periods of higher concentrations of atmospheric carbon dioxide, lower levels of global ice volume, and the subsequent increase in regional moisture-bearing winds
Now that human activities increase levels of atmospheric greenhouse gases, research says, we can expect the same monsoon patterns to emerge.
Steven Clemens, Professor of Earth, Environmental and Planetary Sciences at Brown University and lead author of the study, said, “We can confirm that over the past million years the increase in carbon dioxide in the atmosphere has been followed by a significant increase in rainfall in the South Asian Monsoon system. ”The climate model predictions are“ wonderfully consistent with what we’ve seen over the past million years, ”he said.
Anders Levermann, professor of dynamics of the climate system at the Potsdam Institute in Germany, who was not involved in the new paper but carried out research on monsoon projections from climate models, said he was pleased with the research that forward the results. supports -Search for climate models. “It’s a tremendous amount of information,” he said, “and it’s really nice to see actual data that reflects more than a million years of our planet’s history, like the laws of physics that we use every day experience, their footprints in this extreme form leave a rich Paleo record. “
Dr. Levermann added that the consequences for the people of the Indian subcontinent were devastating; the monsoons already drop tremendous amounts of rain and “can always be destructive,” he said, but the risk of “catastrophically strong” seasons is growing and the increasingly unpredictable nature of the seasons has its own risks. “And it hits the greatest democracy in the world; the most challenged democracy in the world in many ways, ”he said.
Dr. Clemens and other researchers took their samples during a two-month research trip on a converted oil drilling ship, the JOIDES Resolution. It carried a crew of 100 and 30 scientists on a journey that began in November 2014. “We were out over Christmas,” he recalled, and although “it’s difficult to be away from family for so long,” the payoff has finally arrived. “We were there this year,” he said, “creating these data sets. It is satisfying that this is finally coming out. “