4th March 2025 (14 Topics)
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Marine Heat Waves (MHWs)
Context
A new study published in Nature Climate Change highlights a 240% increase in marine heatwave (MHW) days during the summers of 2023-24, compared to historical records. MHWs affected every ocean region, causing extreme weather events, ecosystem collapses, and economic losses.
Key Findings from 2023-24 Marine Heatwaves
- Sea Surface Temperature (SST) Records: 10% of global oceans recorded highest-ever SSTs. SSTs were four times higher than the annual historical average.
- Extreme Weather Events Triggered:
- United Kingdom, North America & Japan: Heatwaves
- Ecuador, Libya, Japan, Australia: Severe flooding
- Atlantic Hurricane Season: Near-record number of storms (cyclones)
- Cyclone Gabrielle (New Zealand)
- Cyclone Mocha (Bay of Bengal, May 2023)
- Cyclone Remal (Bay of Bengal, May 2024)
- Long-Term Projections for the Indian Ocean
- Past Warming Rate (1950-2020): 2°C per century
- Future Warming Rate (2020-2100): 7°C - 3.8°C per century
- Regions at Highest Risk: Northwestern Indian Ocean (Arabian Sea)
What are marine heat waves?
- A marine heat wave is an extreme weather event.
- It occurs when the surface temperature of a particular region of the sea rises to 3 or 4 degree Celsius above the average temperature for at least five days.
- MHWs can last for weeks, months or even years.
- Factors contributing to Marine Heat Waves:
- Global Warming:Rise in temperatures due to Anthropogenic events, has led to an increase in global temperatures which ultimately contributes to ocean warming.
- El Nino:Winds can enhance or suppress the warming in a marine heatwaves, and climate models like El Niño can change the likelihood of events occurring in certain regions.
- Ocean currents:The most common drivers of marine heatwaves include ocean currents which can build up areas of warm water and air-sea heat flux, or warming through the ocean surface from the atmosphere.
Impact of MHWs in 2023-24
- Physical & Climatic Impacts: 23 records of extreme events. Cyclones, flooding, heatwaves, heavy rainfall, dam collapses
- Biological & Ecological Impacts: 43 records of ecosystem damage. Coral bleaching in Japan, Peru, and other regions
- Fish die-offs in the Gulf of Thailand & Gulf of Mexico
- Food web disruptions (lower phytoplankton ? decline in fish/seabird populations)
- North Atlantic species moving to the Arctic (Oct 2023)
- Whale & dolphin strandings (South Pacific, Jan 2024)
- Fan mussel (Mediterranean) threatened with extinction
- Destroying kelp forest: MHWs destroy kelp forests and fundamentally altered the ecosystem of the coast.
- Disturbs food web: MHWs also fuel the growth of invasive alien species, which can be destructive to marine food webs.
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