The rise in temperatures has been highest in the Northwestern Indian Ocean, including the Arabian Sea.
Sounding a massive warning bell, a study has revealed that the warming of the Indian Ocean is going to lead to the worsening of severe cyclones and heavy rainfall events and that the world's third-largest water body is heading towards a near-permanent heatwave state.
The study said that the Indian Ocean and its surrounding countries face the highest risk of natural hazards. This is particularly important because the ocean is bordered by 40 countries, which are home to a third of the global population, and climatic changes in the region have major societal and economic impacts. The effects are expected to be more severe in and around India as the rise in seawater temperatures has been highest in the Northwestern Indian Ocean, including the Arabian Sea.
The study, led by Roxy Mathew Koll of the Indian Institute of Tropical Meteorology Pune, also states that the warming will contribute to rising sea levels and a reduction in marine productivity, all of which will threaten the livelihoods of people on the coast, many of whom are dependent on fishing.
Severe Weather Events, Permanent Heatwave
Published by Elsevier, the study warns that the seasonal cycle of surface temperatures is projected to shift in the years to come, which may lead to an increase in extreme weather events over the Indo-Pacific region.
Measured as 'maximum basin-average temperatures' the temperature in the Indian Ocean between 1980 and 2020 was between 26 degrees and 28 degrees Celsius throughout the year and the study has warned that, in a high emission scenario, even the minimum temperature by the end of this century will be above 28 degrees Celsius - between 28.5 degrees and 30.7 degrees.
It states that, with ocean temperatures rising, extremely severe cyclones and heavy rainfall events - which have already gone up since the 1950s - are projected to only increase in number.
Another factor which is likely to contribute to such events is marine heatwaves, which are periods of extremely high temperatures in the ocean. These are expected to increase over 10 times from 20 days a year to a whopping 220-250, pushing the tropical Indian Ocean into what the study calls a "near-permanent heatwave state".
Marine heatwaves cause a rapid intensification of cyclones - where a cyclone goes from a depression to a severe category in just a few hours. They also lead to coral bleaching and the destruction of seagrass and kelp forests, which can have a major negative impact on the fisheries sector.
The lead author, Roxy Matthew Koll said, "It is crucial to recognise that the impacts of these changes are not distant concerns for our grandchildren and future generations alone. As the current generation, we are already witnessing the repercussions firsthand. Monsoon floods, droughts, cyclones, and heatwaves over both land and ocean are increasingly affecting us.
"These extreme weather events will amplify in intensity and frequency before we reach the twilight of our time - unless decisive action to adapt and mitigate climate change is taken now," he warned.
Monsoon Impact?
The Indian Ocean Dipole, a climate pattern that affects the monsoon and cyclone formation, is also predicted to change. The study says that the frequency of extreme dipole events is predicted to increase by 66% whereas moderate events will decrease by 52% by the end of the 21st century. This could spell bad news for monsoon-dependent India.
While the Indian Ocean warmed at a rate of 1.2 degrees Celsius per century in the 70 years between 1950 and 2020, the study said climate models predict the warming will accelerate and go up to between 1.7 and 3.8 degrees Celsius until 2100.
The warming in the Indian Ocean is not limited to the surface and extends to a depth of 2,000 metres. "The future increase in heat content is comparable to adding the energy equivalent of one Hiroshima atomic bomb detonation every second, all day, every day, for a decade," Mr Koll said.
Increasing heat in the ocean also contributes to a rise in sea levels. The study said thermal expansion of water contributes to more than half of the sea level rise in the Indian Ocean, which is even more than the contribution from the melting of glaciers and sea ice.
Acidification To Increase
Ocean acidification is also predicted to go up, with pH levels at the surface decreasing from above 8.1 to below 7.7 by the end of the century.
"The projected changes in pH may be detrimental to the marine ecosystem since many marine organisms-particularly corals and organisms that depend on calcification to build and maintain their shells-are sensitive to the change in ocean acidity. The change may be easier to fathom when we realize that a 0.1 fall in human blood pH can result in rather profound health consequences and multiple-organ failure," Mr Koll said.
The study calls for taking a multifaceted approach to addressing the problem of warming, including decreasing carbon emissions, and the authors have also asked for action to be taken immediately.
"The Indian Ocean, a climate change hotspot, faces rapid and strong increases in marine heatwave frequency and intensity unless global CO2 emissions are substantially cut," Thomas Frolicher, one of the authors, said.