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The marine heatwaves (MHWs) linked to the death of more than 30,000 fish off the coastal Western Australia in January were made up to 100 times more likely to occur due to climate change, according to a new analysis. The MHWs began in September 2024 and are still ongoing in the region.
The analysis was carried out by the non-profit group Climate Central. It also said the severity of the MHWs is still intensifying as sea surface temperatures (SST) in some areas touched 2 degrees Celsius or more above average for this time of year.
The current MHWs are the second-worst in Western Australia’s recorded history. The region saw its most intense MHWs during the 2010–11 summer, when temperatures soared to 5 degrees Celsius above average, peaking in February and March, according to a report by the University of Western Australia.
A marine heatwave is an extreme weather event. It occurs when the surface temperature of a particular region of the sea rises to 3 or 4 degrees Celsius above the average temperature for at least five days. MHWs can last for weeks, months or even years, according to the US government’s agency National Oceanic and Atmospheric Administration (NOAA).
In the past few decades, MHWs have become longer-lasting, more frequent, and intense, according to a 2018 study, ‘Marine heatwaves under global warming’, published in the journal Nature. “Between 1982 and 2016, we detected a doubling in the number of MHW days,” the analysis said.
A 2021 report by the International Union for Conservation of Nature (IUCN) said MHWs have increased by 50% over the past decade and now last longer and are more severe. “MHWs can last for weeks or even years. They can affect small areas of coastline or span multiple oceans. MHWs have been recorded in surface and deep waters, across all latitudes, and in all types of marine ecosystems,” the report said.
The primary reason is the climate crisis. As global temperatures have soared to 1.3 degrees Celsius above the pre-industrial levels, 90% of the extra heat has been absorbed by the ocean. This has increased the global mean SST by close to 0.9 degrees Celsius since 1850, and the rise over the last four decades is around 0.6 degrees Celsius, according to the Copernicus Climate Change Service. As a result, MHWs have become more frequent, long-lasting, and severe.
That is why coastal Western Australia has been witnessing a spike in MHWs and their intensity, which is steadily increasing. The Climate Central report said, “In September [2024], average temperature anomalies stayed at around 1.2 degrees Celsius. Since then, average temperature anomalies have steadily increased. In January [2025], mean temperature anomalies never dipped below 1.6 degrees Celsius, and broke above 2 degrees Celsius on three separate occasions.”
The situation is expected to get worse not only in Western Australia but across the world. The 2018 study said the current number of MHWs is projected to increase on average by a factor of 16 for global warming of 1.5 degrees Celsius and by a factor of 23 for global warming of 2.0 degrees Celsius.
MHWs can be devastating for marine life. For example, the 2010-11 MHWs in Western Australia caused large-scale fish kills — the sudden and unexpected death of many fish or other aquatic animals over a short period and mainly within a particular area. It also destroyed klep forests and fundamentally altered the ecosystem of the coast. Kelps usually grow in cooler waters, providing habitat and food for many marine animals.
These heatwaves contribute to coral bleaching, which reduces the reproductivity of corals and makes them more vulnerable to life-threatening diseases. Thousands of marine animals depend on coral reefs for survival and damage to corals could, in turn, threaten their existence.
In 2024, coral bleaching on Australia’s Great Barrier Reef reached “catastrophic” levels after intense MHWs put corals under stress. This was the reef’s seventh mass bleaching event.
