‘Fast running out of time to turn the tide’: Australia at sea in vast marine heatwave

A marine heatwave causing extreme heat and rainfall has enveloped Australia and stretched for 40 million square kilometres across the south-west Pacific, bringing intense heat, extreme rainfall and sea-level rises.

The World Meteorological Organisation has confirmed 2024 was the hottest year on record in the south-west Pacific, which spans more than 10 per cent of the global ocean surface area. Sea surface temperatures were the highest on record and ocean heat content was at near-record levels in 2024.

The State of the Climate in the South-West Pacific 2024 report outlined deadly impacts, including a record-breaking streak of tropical cyclones that hit the Philippines, existential threats to a tropical glacier in Indonesia’s New Guinea. Marine heatwaves in the south-west Pacific extended for nearly 40 million square kilometres, over 10 per cent of the global ocean surface area.

Across the region, the average temperature was almost half a degree warmer than the 1991–2020 average. Ocean warming and accelerated loss of ice mass from the ice sheets contributed to the rise of the global mean sea level by 4.7 millimetres per year between 2015 and 2024, reaching a new record observed high in 2024, the organisation’s report found.

“Sea-level rise is an existential threat to entire island nations,” the secretary-general of the World Meteorological Organsiation, Celeste Saulo, said. “It is increasingly evident that we are fast running out of time to turn the tide.”

It is estimated that each year, at least 50,000 Pacific islanders face the risk of displacement due to the adverse effects of climate change.

The waters around Australia have had a prolonged marine heatwave, not just in the Pacific but also the Indian and Southern oceans.

Associate Professor Alex Sen Gupta, from the University of New South Wales Climate Change Research Centre, said that not only were marine temperatures around Australia at a record last year, there was a massive jump in heat from the previous record set the year prior.

“Marine heatwaves push plants and animals beyond their thermal limits, which means they can suffer damaging effects, including high levels of mortality in some cases,” Sen Gupta said.

“In 2024 for example we again saw mass bleaching and mortality throughout the Great Barrier Reef and massive [wild] fish kills off Western Australia.”

The marine heatwave is also linked to a mortality event that killed nearly 7 million farmed salmon in Tasmania, based on mandatory reporting to the state’s Environment Protection Authority, and a massive algal bloom in South Australia.

Sen Gupta said the marine heatwaves would become more frequent and more intense until greenhouse gas emissions were cut.

“Despite all the talk, we are still pumping more CO2 into the atmosphere each year,” he said.

Separately, World Weather Attribution has put out its analysis of the floods that hit the NSW Mid North Coast in May, but the results were inconclusive.

An earlier study by ClimaMeter, put out within two days of the Taree flood, linked the event to climate change, but there is scientific debate about the validity of these rapid studies.

World Weather Attribution, a project of Imperial College London, takes longer to produce its studies, but uses more methodologies to verify the findings. In this case, the results were mixed.

When World Weather Attribution compared the event with the same scenario in a climate 1.3 degrees cooler, using data for an entire year, the researchers found the likelihood had doubled, and the intensity was at least 10 per cent greater.

But if they isolated the event to the April-June period, the likelihood and intensity appeared to decrease.

Regardless of whether climate change or natural climate variability is the cause of an individual weather event, the incidence of extreme rainfall in a short duration is expected to increase with global warming.

A warmer atmosphere can hold more moisture – about 7 percentage points of humidity for every degree of warming. Atmospheric temperatures have already risen 1-1.5 degrees since the industrial revolution.

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