Global warming is leading to deadly heatwaves in the atmosphere and oceans. Due to anthropogenic greenhouse gas emissions, oceans trap and store 91% of excess heat in the climate system. The process has led to a rapid rise in sea surface temperatures worldwide. The definition of a marine heatwave is where extreme temperatures last for at least five days (SST) and where Sea Surface Temperatures exceed the “seasonally-varying 90th percentile threshold based on the 1970–1999 reference period or hotter than 90% of the typical temperatures for each season”. In the Indian Ocean, a rapid increase in the ocean averages of one degree Celsius (1.8 F) throughout 1951-2015 “at a rate of 0.15 degree Celsius per decade.” That may not sound like much. Still, it takes enormous solar energy to heat water to that degree.
The ocean has experienced rapid warming, but the Indian Ocean stands apart from other ocean basins, where the heat content can be 328 feet deep. A new study has found that marine heatwaves are expected to soar from 20 episodes to 225 to 250 episodes per year by 2050.
The findings of this new research, led by Roxy Mathew Koll, scientist with Climate Research Lab, Indian Institute of Tropical Meteorology (IITM), Pune, are published in a recent book, The Indian Ocean and its Role in the Global Climate System, released on April 26.
“In the present-day climate scenario, where we are experiencing 1.2-degree Celsius warming, marine heat waves have already emerged in the Indian Ocean and are rising; at present, they range up to 20 days a year,” said Koll, talking to Mongabay India about the implications of prolonged marine heatwaves in the Indian Ocean. “But, by 2050, we are expected to breach the two-degree Celsius mark, and these heatwaves are likely to increase to 220-250 days, which is two-thirds of a year. We are calling it a permanent heatwave state for the Indian Ocean,” he said.
“These prolonged marine heatwaves will not only intensify cyclones but also affect fish migration, coral reefs, phytoplanktons and marine biodiversity,” warned Koll, who is also the lead author of the Intergovernmental Panel on Climate Change (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate.
The projected heat waves in the Indian Ocean are of concern as nearly 250 million people live within 50 km of the Indian coastline (3.5% of the world’s population). The 8,118-km long coastline is also home to more than seven million people who depend on fishing for their livelihood.
The bottom line is that cyclones and typhoons will become more powerful and intense, disrupting the water cycle and making heat, drought, and wildfires more likely. Fears grow that the current classification of cyclones from 1 to 5 may no longer serve the purpose; a new category, 6, will be necessary to warn people of extreme and deadly danger.
Those who depend on fishing for protein intake will be impacted, as the heat content already forces fish to migrate to cooler waters or dive ever deeper to escape the heat. Algae have become a concern in the Arabian Sea, and at depth, the heat prevents water mixing, meaning the nutrients critical for mesoscopic plants (the base of the marine food chain) are below the subsurface of the water column.
One of the more visible aspects is the bleaching of coral reefs. Although reefs take up only one percent of the ocean, they are responsible for twenty-five percent of marine life.
While ocean currents and winds in the Atlantic and Pacific can disperse heating water, the large Asian landmass to the north of the Indian Ocean makes it particularly susceptible to retaining heat. “It’s quite different to the tropical Atlantic and tropical Pacific events. There you have you have steady easterly trade winds. In the Indian Ocean that’s not the case,” Ummenhofer said.
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“There is a certain season where you have easterly winds. Otherwise you have seasonally reversing monsoon winds, which makes for very different dynamics.”
Recent research suggests ocean heat has risen dramatically over the past decade, leading to the potential for warming water in the Indian Ocean to affect the Indian monsoon, one of the most important climate patterns in the world.
“There has been research suggesting that Indian Ocean dipole events have become more common with the warming in the last 50 years, with climate models suggesting a tendency for such events to become more frequent and becoming stronger,” Ummenhofer said.
She said warming appeared to be “supercharging” mechanisms already existing in the background. “The Indian Ocean is particularly sensitive to a warming world. It is the canary in the coalmine seeing big changes before others come to other tropical ocean areas.”
Meanwhile, relentless scorching heat punishes Southeast Asia, and it is only the beginning of May. People are dying, agriculture is failing, schools are closed, health care facilities are overwhelmed, and only misery for those not in air conditioning.
The face of the world that we pretend does not exist.