Is a near-permanent heatwave coming to the Indian Ocean?

Amidst the sweltering heatwaves gripping various parts of India during the ongoing seven-phase general elections, a broader concern emerges – the looming threat of heatwaves extending their reach into the vast expanse of the Indian Ocean.

As citizens navigate the polls amidst fears of heat-related illnesses, a recent study unveils troubling projections for the future of the region’s marine ecosystems.

The study titled “Future Projections for the Tropical Indian Ocean,” led by Roxy Mathew Koll, a scientist at the Indian Institute of Tropical Meteorology (IITM) in Pune, sheds light on the Indian Ocean’s rapid warming trend.

Published in the recent book “The Indian Ocean and its Role in the Global Climate System,” the research foresees a concerning trajectory – the Indian Ocean hurtling towards a state of near-permanent marine heatwaves. According to Koll, projections suggest an alarming increase, with 220-250 days of such events annually expected by 2050.

What are the implications of prolonged heatwaves?

Koll emphasises the multifaceted repercussions of prolonged marine heatwaves, ranging from the intensification of cyclones to disruptions in fish migration patterns and coral reef ecosystems. Such events pose significant risks to marine biodiversity and the livelihoods of millions of individuals dependent on the oceanic ecosystem for sustenance and economic well-being.

The projected heatwaves cast a shadow over densely populated coastal regions, where approximately 250 million people reside within close proximity to the Indian shoreline. Moreover, over seven million individuals rely on fishing as their primary livelihood, amplifying the socio-economic stakes of environmental upheaval and ecosystem degradation.

Rising temperatures in the Indian Ocean

Global warming exacerbates the warming of oceans, with approximately 91% of excess heat energy trapped in the Earth’s climate system stored within these vast water bodies. The term “marine heatwave,” coined relatively recently, describes events wherein ocean temperatures soar to extreme levels and persist for a minimum of five days.

Disturbingly, the tropical Indian Ocean has experienced a swift escalation in ocean warming, with sea surface temperatures (SST) rising by an average of one degree Celsius between 1951 and 2015.

Expressed as ‘maximum basin-average temperatures,’ the Indian Ocean maintained a range of 26 to 28 degrees Celsius throughout the year between 1980 and 2020. However, a recent study cautions that, under a high emission scenario, even the minimal temperature by the century’s end is anticipated to surpass 28 degrees Celsius, ranging between 28.5 and 30.7 degrees.

The study highlights that escalating ocean temperatures are correlated with a heightened frequency of extremely severe cyclones and intensified rainfall events, a trend already observable since the 1950s.

Additionally, the proliferation of marine heatwaves, characterised by prolonged periods of exceptionally high ocean temperatures, is poised to surge dramatically. Anticipated to surge from a mere 20 days annually to a staggering 220-250 days, these events are forecasted to thrust the tropical Indian Ocean into what the study terms a “near-permanent heatwave state.”

Catalysts of Cyclone intensity

Elevated water temperatures associated with marine heatwaves serve as catalysts for extreme weather phenomena, including tropical storms and cyclones.

Research indicates that a significant proportion of cyclones in the Bay of Bengal and the Arabian Sea are preceded by marine heatwaves, facilitating rapid intensification and posing heightened risks to coastal communities.

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.

Fishing communities, already grappling with existential challenges, face exacerbated risks due to the intensification of cyclones and disruptions in marine ecosystems. Cyclone-induced bans on fishing activities, compounded by dwindling fish stocks and habitat degradation, jeopardise the livelihoods of coastal inhabitants, exacerbating socio-economic disparities, reported Mongabay.

How will monsoons be impacted?

The Indian Ocean Dipole, a climatic phenomenon influencing the monsoon and cyclone genesis, is poised for transformation. According to the study, extreme dipole events are projected to surge by 66%, while moderate occurrences will decline by 52% by the close of the 21st century. Such alterations could spell ominous implications for India, heavily reliant on the monsoon for agricultural sustenance.

Despite the Indian Ocean experiencing a warming trend of 1.2 degrees Celsius per century over the past seven decades, climate models indicate a forthcoming acceleration. Projections suggest a temperature surge ranging between 1.7 and 3.8 degrees Celsius by 2100, exacerbating the warming trajectory.

The escalating temperatures within the Indian Ocean extend beyond surface levels, penetrating depths of up to 2,000 meters.  “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,” Koll said.

Furthermore, the intensifying oceanic heat contributes to a concurrent rise in sea levels. Notably, the study emphasises that thermal expansion of water accounts for over half of the sea level elevation in the Indian Ocean, surpassing even the contribution from glacier melt and sea ice depletion.

Ocean acidification to go up

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 realise that a 0.1 fall in human blood pH can result in rather profound health consequences and multiple-organ failure,” Koll said.

“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.

Addressing the multifaceted challenges posed by near-permanent marine heatwaves demands a comprehensive strategy encompassing scientific research, policy interventions, and community engagement. Improved early warning systems, coupled with adaptive measures tailored to the needs of vulnerable populations, are imperative to mitigate the socio-economic and environmental toll of escalating heatwaves.

With inputs from agencies