Marine Heatwaves (MHWs)

News: The marine heatwaves (MHWs) off the coast of Western Australia have led to the death of over 30,000 fish in January 2025. These heatwaves, which began in September 2024, are still ongoing and have been intensifying over time.

About Marine Heatwaves (MHWs)

• Marine heatwaves (MHWs) are extreme weather events where the sea surface temperature (SST) rises by 3 to 4 degrees Celsius above the average for at least five consecutive days. 
• These events can persist for weeks, months, or even years, impacting marine ecosystems. 
• According to the National Oceanic and Atmospheric Administration (NOAA), marine heatwaves have become more frequent, intense, and long-lasting due to climate change.

Reasons behind Marine Heatwaves Intensification

• The primary driver of intensifying marine heatwaves is climate change. As global temperatures have risen by 1.3 degrees Celsius above pre-industrial levels, oceans have absorbed 90% of the excess heat.
• As a result, the global mean sea surface temperature has increased by 0.9 degrees Celsius since 1850 and 0.6 degrees Celsius in the last four decades, according to the Copernicus Climate Change Service. 
• A 2018 study predicted that the number of marine heatwaves will increase 16 times if global warming reaches 1.5 degrees Celsius and 23 times if it reaches 2 degrees Celsius.

Impact of Marine Heatwaves

• Marine heatwaves have severe consequences for marine ecosystems. 
• The 2010–11 heatwaves in Western Australia caused large-scale fish deaths and destroyed kelp forests, which serve as critical habitats for marine life. 
• These heatwaves also contribute to coral bleaching, which weakens corals, reduces their reproductive ability, and makes them more vulnerable to diseases. 
• In 2024, the Great Barrier Reef experienced catastrophic coral bleaching, marking its seventh mass bleaching event, due to prolonged exposure to marine heatwaves.