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IITM Study Shows Tenfold Increase in Marine Heatwaves


A recent study conducted by the Indian Institute of Tropical Meteorology (IITM) in Pune has revealed a significant surge in marine heatwaves, potentially leading to intensified cyclones. The study indicates a staggering tenfold increase in marine heatwave duration, escalating from 20 days to 220–250 days per year.


GS I: Geography

Dimensions of the Article:

  1. Key Findings of the Report
  2. Marine Heatwave

Key Findings of the Report:

Temperature Rise in the Indian Ocean:

  • Indian Ocean temperature rose by 1.2°C from 1950 to 2020.
  • Projected increase by 1.7°C to 3.8°C from 2020 to 2100.

Increase in Marine Heatwave Days:

  • Predicted rise from 20 days/year to 220–250 days/year.
  • Linked to quicker cyclone formation and potential permanent heatwave state.

Impacts on Marine Ecosystems:

  • Likely acceleration of coral bleaching, seagrass destruction, and loss of kelp forests.
  • Significant implications for the fisheries sector.

Escalation of Overall Heat Content:

  • Increase extends to depths of 2,000 meters.
  • Currently increasing at 4.5 zetta-joules per decade.
  • Expected to grow at 16–22 zetta-joules per decade.

Sea-Level Rise and Indian Ocean Dipole (IOD):

  • Thermal expansion contributes over half of the sea-level rise.
  • IOD likely to experience increased extreme events and decreased moderate events.
  • Positive phases of IOD favor the summer monsoon.

Monsoon Prediction for 2024:

  • Despite ongoing heatwaves, “above-normal” monsoon expected for June-September 2024 due in part to positive IOD phase.
Impact of Rising Sea Levels on India:

Sea Level Rise Trends:

  • Sea level along the Indian coast rising at about 1.7 mm/year during 1900-2000.
  • 3 cm rise could intrude the sea inland by about 17 meters.

Vulnerability of India:

  • Most vulnerable to compounding impacts of sea level rise.
  • Indian Ocean warming contributes significantly to sea level rise.
  • Indian Ocean fastest-warming ocean in terms of surface warming.

Compound Extreme Events and Cyclones:

  • Cyclones intensifying rapidly due to ocean warming.
  • Increased flooding due to compounding sea level rise and storm surges.
  • Cyclones bringing more rain than before.
  • Example: Super Cyclone Amphan (2020) causing extensive flooding and saline water intrusion.

Long-term Implications:

  • Indus, Ganga, and Brahmaputra rivers may shrink.
  • Rising sea levels combined with saltwater intrusion making parts of deltas uninhabitable.

Marine Heatwave:

  • Marine heatwaves are prolonged periods of abnormally high Sea Surface Temperature (SST).
  • These events can lead to coral bleaching, seagrass destruction, and loss of kelp forests, impacting the fisheries sector negatively.
  • Common drivers of marine heatwaves include ocean currents that accumulate warm water and air-sea heat flux, which is warming from the atmosphere through the ocean surface.
  • Winds can amplify or dampen the warming effects of a marine heatwave, and climate modes like El Niño can influence the occurrence of these events in specific regions.

Impact of Marine Heatwave on Rainfall in Northwest India:

  • The marine heatwave in the Bay of Bengal elevated sea surface temperatures, resulting in increased evaporation rates and a higher supply of moisture in the atmosphere.
  • This surplus moisture contributed to above-average rainfall in northwest India.
  • The marine heatwave likely influenced the formation and behavior of low-pressure systems called depressions in the Bay of Bengal.
  • These depressions play a significant role in monsoon and rainfall patterns.
  • The marine heatwave, along with changing timescales of depressions, affected the path and trajectory of these weather systems.
  • Depressions were more inclined to move towards northwest India rather than north-central India, leading to a concentration of rainfall in the northwest region and resulting in above-average rainfall in that area.

Impacts of Marine Heatwaves:

  • Ecosystem Structure: Marine heatwaves can alter ecosystem structure by favoring certain species while suppressing others.
  • Mass Mortality: Marine heatwaves have been associated with mass mortality events in marine invertebrates, leading to significant ecological disruptions.
  • Behavioral Changes: Species may be forced to change their behavior in response to marine heatwaves, putting them at increased risk of harm.
  • Habitat Range Shifts: Marine heatwaves can cause shifts in the habitat ranges of species, resulting in changes to ecosystem dynamics. For example, the expansion of spiny sea urchins into new areas can negatively impact kelp forests.
  • Economic Losses: Marine heatwaves can have significant economic impacts, particularly on fisheries and aquaculture industries.
  • Biodiversity Loss: Marine heatwaves can lead to drastic declines in biodiversity, affecting the overall health and functioning of marine ecosystems.
  • Corals and Bleaching: Marine heatwaves can cause widespread coral bleaching, leading to coral mortality and ecosystem degradation.
  • Interaction with Other Stressors: Marine heatwaves often occur alongside other stressors such as ocean acidification, deoxygenation, and overfishing. These combined stressors can further damage habitats and increase the risks of deoxygenation and acidification in affected areas.

-Source: The Hindu

May 2024