Study of sea sponges lead scientists to believe Earth has already passed 1.5 degrees Celsius of warming

Earth may have already passed 1.5 degrees Celsius of warming and could be soon heading for 2 degrees of warming, researchers have found after studying sea sponges in the Caribbean.

The study of 300 years of ocean temperature records kept preserved within sea sponges in the Caribbean indicate that global mean surface temperatures may have already exceeded 1.5 degrees Celsius and that a 2-degree Celsius rise could be possible by the end of the decade, according to a paper published in Nature Climate Change on Monday.

While limiting global warming to 1.5 degrees Celsius since the Industrial Revolution was outlined when the United Nations Framework Convention on Climate Change created the Paris Agreement, the exact figure is less important than keeping global warming as far below that figure as possible. The likelihood of doing so is waning, though, according to climate scientists.

Samples of sclerosponge skeletons found in the eastern Caribbean, where the natural variability of temperatures is less than at other locations, indicate that the pre-industrial period can be defined by stable temperatures from 1700 to 1790 and from 1840 to 1860, with the gap defined by cooling related to volcanic activity, according to the study. The sea sponges revealed that warming related to human activity commenced from the mid-1860s, with clear emergence by the mid-1870s, about 80 years before the period indicated by instrumental sea surface records.

The sclerosponge is a long-lived species that records chemical changes in its calcium carbonate skeleton, serving as a natural archive of ocean temperatures, according to the paper.

The sponges only exist in the Caribbean, Amos Winter, a professor at Indiana State University's department of earth and environmental systems, told reporters at a news conference on Friday. Divers ventured up to 100 meters below the sea surface to obtain the sponges, Winter said.

The findings have implications for current projections of global warming, the researchers said. The authors estimate that 1.5 Celsius of warming may have been reached and that a mean surface warming of 1.7 Celsius could have occurred between 2018 and 2022.

"The industrial era of warming commenced earlier than we then was thought -- in the mid 1860s," Malcolm McCulloch, a professor of isotope geobiochemistry at the University of Western Australia and lead author of the study, told reporters during a news conference on Thursday. "Since then, the increasing global mean surface temperatures, which means global warming, has been half a degree greater than the current accepted estimates."