The world's oceans are heating up faster than previously thought, new research has found.
Scientists say it's the strongest sign yet climate change is accelerating, as the heat of the oceans isn't affected by day-to-day variations in weather, like on land.
Researchers at the University of California went over four recent papers detailing changes beneath the waves. They found not only are the oceans getting warmer, but the rate of change is speeding up.
"While 2018 will be the fourth warmest year on record on the surface, it will most certainly be the warmest year on record in the oceans, as was 2017 and 2016 before that," said Zeke Hausfather, who co-authored the latest research.
"The global warming signal is a lot easier to detect if it is changing in the oceans than on the surface."
More than 90 percent of the excess energy trapped on Earth by greenhouse gases is soaked up by the ocean. Even if melting of the polar ice caps stopped completely - which won't happen - the expected best-case scenario of a 0.78degC rise in ocean temperatures by the end of the century will still see sea levels rise by 30cm worldwide, thanks to thermal expansion.
Climate change sceptics have long pointed to an apparent cooling of the climate in the decade after 1998's peak as evidence it's all a hoax, but Mr Hausfather says recent measurements have put the debate to rest.
"These four new records that have been published in recent years seem to fix a lot of problems that were plaguing the old records, and now they seem to agree quite well with what the climate models have produced."
The latest report from the Intergovernmental Panel on Climate Change (IPCC) warned unprecedented action was needed to stop hundreds of thousands of species going extinct, natural environments dying and coastal communities being flooded out of existence.
The Paris Agreement saw nations pledge to work to keep temperature rises below 2degC, but the IPCC's latest report says that has to come down to 1.5degC.
Victoria University climate scientist James Renwick warns at present rates of carbon dioxide emission, it'll rise by another 1degC in just the next two decades.