CAUSE AND EFFECT | Marine heatwaves pose a threat we need to prepare for. Now. - Hindustan Times
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CAUSE AND EFFECT | Marine heatwaves pose a threat we need to prepare for. Now.

ByTannu Jain
Jun 04, 2023 06:45 PM IST

As global average air temperatures rise, so does the probability of marine heatwaves with oceans absorbing nearly 90% of the excess heat

The year is 1958, and a meteorite crash in Pennsylvania, United States, has brought a carnivorous alien into town. The alien consumes everyone and everything in its path, growing and becoming more aggressive in the process.

The warm patch of water in the Pacific Ocean, known as The Blob, brought unusual heat to parts of the world. Water temperature inside the blob reached 2.5 degrees Celsius (pictured here) above normal in many places. (Wiki Commons) PREMIUM
The warm patch of water in the Pacific Ocean, known as The Blob, brought unusual heat to parts of the world. Water temperature inside the blob reached 2.5 degrees Celsius (pictured here) above normal in many places. (Wiki Commons)

This is the plot of the science-fiction horror film: The Blob.

Cut to 2013, a huge patch of mysteriously warm ocean water forms in the Gulf of Alaska and begins to spread. The pool of water lingers through the winter, quickly expanding south along the Pacific Coast. By the summer of 2014, it stretches from Alaska to Mexico.

This unusual patch of warm water in the otherwise frigid Pacific, however, is very real and is nicknamed, The Blob.

Though unscientific, the term coined by climate scientist Nick Bond at the University of Washington in Seattle, quickly caught on as researchers across the world were left puzzled by the thousands of seabirds that washed up dead on the shores, and a toxic algal bloom that suffocated much of marine life.

Like its namesake, The Blob left destruction in its path and prompted years of research into marine heatwaves (MHW).

According to experts, “The Blob that cooked the Pacific” (as National Geographic called it) formed by an atmospheric ridge of high pressure over Alaska that disrupted the winds, causing fewer storms along the West Coast, reduced upwelling, and led to ripe conditions for algal blooms.

Water temperature inside the blob reached 2.5 degrees Celsius above normal in many places, and 3 degrees Celsius at its peak. Since then, several researchers and reports have warned of the threat posed by rising ocean temperatures and marine heatwaves.

What is a marine heatwave

An MHW is declared when sea surface temperatures (SST) are anomalously high for at least five consecutive days.

And as global average air temperatures rise, so does the probability of marine heatwaves with oceans absorbing nearly 90% of the excess heat.

In 2020, research by environmental physicist Charlotte Laufkötter from the University of Bern in Switzerland and her colleagues, found that the frequency of such events had already risen 20-fold due to human-induced global warming.

Laufkötter and her colleagues studied the marine heatwaves recorded between 1981 and 2017 and found 300 largest events lasted an average of 40 days, covered an average of 1.5 million sq km, and had a peak temperature of 5°C.

The researchers found that once we reach 1.5°C of global warming, such events could occur up to every decade at worst; by 3°C they could become as regular as annually. The report, ‘High-impact marine heatwaves attributable to human-induced global warming’, was published in Science.

The Intergovernmental Panel for Climate Change, in its sixth assessment report, said the sea surface temperatures have risen by about 0.88 degrees Celsius from the period 1850-1900 to 2011-2020.

"When we have a marine heat wave in 2050, it's going to be way out there — in uncharted territory," Bond told the journal Science in 2019.

But the wait might actually be shorter than the 27 years Bond predicted.

According to a report in The Guardian, over one year ending April 2023, New Zealand’s coastal waters witnessed MHW conditions for 208 days of the 365. And the event is ongoing.

According to a report in The Guardian, over one year ending April 2023, New Zealand’s coastal waters (seen here in a satellite image) witnessed MHW conditions for 208 days of the 365.(Wiki Commons)
According to a report in The Guardian, over one year ending April 2023, New Zealand’s coastal waters (seen here in a satellite image) witnessed MHW conditions for 208 days of the 365.(Wiki Commons)

The blob of 2013-2016 decimated marine life, killing over 100 million Pacific cod, thousands of seabirds, and other animals. It fueled massive toxic algal blooms that shut down fishing industries and led to the deaths of whales and seabirds.

An ongoing shift in the region’s food chain was a reduction in the nutrient-rich plankton, which was replaced by nutrient-poor gelatinous zooplankton.

Back-to-back marine heatwaves in northern Australia in 2016 and 2017 are estimated to have killed more than half the coral reefs.

Back-to-back marine heatwaves in northern Australia in 2016 and 2017 are estimated to have killed more than half the coral reefs. (Wiki Commons)
Back-to-back marine heatwaves in northern Australia in 2016 and 2017 are estimated to have killed more than half the coral reefs. (Wiki Commons)

Recent heatwaves in tropical and subtropical waters have caused the defoliation of seagrass and a decrease in kelp biomass – leading to further release of carbon.

In India, experts have identified 66 MHW events that occurred in the western Indian Ocean region between 1982 and 2018, 21 of these occurred during the summer months of June-September. The north Bay of Bengal region witnessed 94 MHWs, and 34 out of these occurred during the summer, experts said in a 2022 paper, Genesis and Trends in Marine Heatwaves Over the Tropical Indian Ocean and Their Interaction With the Indian Summer Monsoon.

"There is a significant rise in annual MHW frequency during 1982–2018 at a rate of 0.14 events per year for the western Indian Ocean and 0.09 events per year for the north Bay of Bengal. On the other hand, the MHW frequency during the monsoon season is increasing at a rate of 0.04 events per year in the western Indian Ocean region and 0.05 events per year in the north Bay of Bengal,” the researchers said.

Such events impact the monsoon by reducing rainfall over the central Indian subcontinent while enhancing it over the southern peninsula, the researchers found.

This year a disruption in the Indian monsoon is already expected, with an El Nino having settled in.

While the rise of air temperatures is instantly visible (think melting ice on a global scale, and heatstroke on a more personal level), the effects of ocean temperatures might go unnoticed for a while.

It might thus be time to add another clause to the climate finance debate.

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  • ABOUT THE AUTHOR
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    Tannu Jain works with HT's Page 1 team. She writes on the environment and climate change, with a focus on implications at the local and global levels. She is also the author of Cause and Effect, a weekly column for HT Premium.

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