Scientists studying deep-sea sponges have uncovered evidence suggesting global temperatures may have already surged past the 1.5°C warming limit set by the Paris Agreement.
The study, published in Nature Climate Change, found that by 2020, global temperatures had risen 1.7°C above pre-industrial levels—higher than most official climate records suggest.
If correct, this would mean the world is on course to hit 2°C of warming as soon as the late 2020s, almost two decades earlier than expected.
The research is based on Ceratoporella nicholsoni, a type of marine sponge that acts like a natural thermometer.
Found in the Caribbean, these creatures grow incredibly slowly, forming skeletons that trap chemical clues about past ocean temperatures. By analysing the Sr/Ca (strontium-to-calcium) ratio in sponge skeletons dating back 300 years, scientists reconstructed historical sea surface temperatures with remarkable accuracy.
Their findings suggest warming started much earlier than previously thought—around the 1860s, long before modern thermometers began keeping track.
The data also challenges previous estimates by suggesting climate change has already surpassed the crucial 1.5°C benchmark that governments are scrambling to stay within.
Lead author of the study, Amos Winter from the University of Western Australia, said the results show “we have underestimated historical warming and are closer to dangerous climate thresholds than we realised”.
While the findings are striking, they are not yet definitive.
The study relies on an alternative method of measuring past temperatures and while sponges are reliable climate archives, their data needs further validation against other records. Also the sample size was relatively small.
Still, the implications are the rate of warming is higher than we think, pushing the planet into more extreme weather, rising sea levels and harsher climate impacts.
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