International research published in peer-reviewed journal Science said unprecedented underwater heatwaves in 2023 could mean ecosystems are stressed beyond a level from which they can recover.
The Southwest Pacific heatwave in the Tasman Sea from November 2022 to March 2023 stretched further and lasted longer than ever before, triggering alarm among others in the North Atlantic and the Pacific.
They caused major concern among scientists, with University of New South Wales Associate Professor Alex Sen Gupta describing the events as a wake-up call.
However, he cautioned against suggestions a tipping point had been reached.
"A tipping point would indicate that we've passed some threshold and we're not coming back again, but at this point, we don't know if that's true," he told AAP.
He said the "unprecedented increase" in the sea surface temperature in 2023 had continued through to 2025, suggesting there could be long-term change.
That would then cause more heatwaves, coral bleaching and the destruction of other habitat-forming species such as seagrass and kelp forests.
"When these habitat-forming species start degrading or disappearing, obviously this is going to have knock-on effects for the whole ecosystem," he said.
Research published in Science by academics from China's Eastern Institute of Technology in Ningbo found the 2023 marine heatwaves smashed records due to their intensity, duration and size.
"Extraordinary (marine heatwaves) of 2023 may represent a major shift in oceanic and atmospheric conditions, potentially indicating an early signal of a tipping point in earth's climate system," the paper said.
The scientists warned the heatwaves could stress ecosystems "beyond recovery thresholds" with coal reef collapse, displacing fish and destabilising polar ice sheets.
CSIRO climate lead Jaci Brown said the findings aligned with her organisation's work and stressed the increase in marine heatwaves was an example of the impacts of climate change.
"Marine heatwaves are just one example of how our future will play out in ways that we are still figuring out," Dr Brown said.
She called for continued monitoring and modelling of what the future of the earth would look like on top of a reduction in greenhouse gas emissions.
"If we don't, we can't prepare, and we are walking into the unknown with dire consequences for our future food, health and security," she said.
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