How sea sponges are adjusting our climate projections


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Limiting average global warming to 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, above pre-industrial levels has been the benchmark for climate action since at least the 2015 Paris Agreement. New scientific study released in the peer-reviewed journal Nature Climate Change, however, suggests that the world unknowingly exceeded this benchmark in 2020. This would mean that the rate of warming is two decades ahead of projections by the Intergovernmental Panel on Climate Change. climate changes. Climate Change, or IPCC, and that we will cross the 2 degree threshold in the coming years.

Perhaps even more surprising than these findings is the fact that they come from the study of marine sponges. A research team led by Professor Malcolm McCulloch from the University of Western Australia's Ocean Institute analyzed sclerosponges, a primitive species of orange sponge found clinging to the roofs of caves on the ocean floor. Sclerosponges grow extremely slowly – just a fraction of a millimeter per year – and can live for hundreds of years. This longevity partly explains why they can be particularly valuable sources of climate data, given that our understanding of ocean temperatures before 1900 is very unclear.

By taking samples of these sponges, McCulloch's team was able to calculate strontium-to-calcium ratios, which can be used to trace water temperatures back to the 1700s. These ratios were then mapped onto global data data on average water temperature so the team can fill in the holes we had at the beginning of the industrial period, when humans began releasing large amounts of carbon dioxide into the atmosphere.

Because the information collected from the sponges matched ocean temperature records from recent decades, the researchers were able to extrapolate far back into the past to show that the average ocean temperature was lower than assumed by the IPCC.

This discrepancy is not the fault of the IPCC. Existing records of ocean temperatures only date back to the 1850s, when sailors threw buckets over the sides of their ships to measure water temperatures. The reliability of these older records is compromised by a number of factors, including the lack of a standardized procedure and the faulty 19th century thermometers. Even beyond these flaws, the surveys only captured surface water temperatures, which are highly variable and easily influenced by weather, unlike deep sea temperatures. 'Were collected only along the main shipping routes of the time, meaning that only parts of the northern hemisphere were covered for many years.

Yet until this week's study, there were few alternative ways to determine average ocean temperatures before widespread industrialization and rampant carbon pollution. This is why the IPCC relies on the pre-industrial period between 1850 and 1900, well after the start of the industrial revolution.

Ocean temperatures collected from the sclerosponges used in the new study may be more reliable than documentary records for several reasons. On the one hand, sponges originate well below the surface layer of the sea, in the so-called mixed ocean layer, where there is a constant tumult of water and atmosphere. Much more stable and reliable temperatures can be recorded in this part of the ocean, McCulloch told Grist. “There is no other natural variability, other than that which comes from the atmosphere,” he said.

And because the sponges were sampled in the Caribbean, where major ocean currents like the Atlantic Southerly Overturning Circulation and the El Niño Southern Oscillation do not distort water temperatures, the differences in heat that What they reveal can more easily be attributed to global warming patterns. “It conveys the signal of ocean warming very well,” McCulloch said of the study sample.

So why sponges? Much research has been done on corals (McCulloch himself spent most of his career studying them), but corals do not lend themselves well to temperature studies. “They're pretty complicated creatures to work with, actually,” McCulloch said, “because they have a lot of biological control over how they register temperature.”

Sclerosponges, on the other hand, are simpler: they build their skeletons by pumping seawater in and out. “They don't seem to be messing around too much with the composition of the calcifying fluid,” McCulloch added. Additionally, they have already demonstrated reliability in carbon isotope analyzes (used to track the burning of fossil fuels) and are found in the mixed layer of the ocean, the best place to perform temperature analysis.

The study began in earnest in 2013, and more in-depth sample collection took place in 2017, when divers were sent to chisel sponges from underwater walls. (They don't like to be disturbed.) These samples were cut in half and McCulloch took his halves back to Australia in his luggage. Back in the lab, samples were taken from each sponge length of 0.5 millimeters, the equivalent of about two years of sponge life, from outer layer to core. The samples were then tested to determine their age with uranium series dating, as well as strontium/calcium ratios and for carbon and boron isotopes. (Boron is used to calculate pH levels.)

Although the new paper managed to convince skeptics of its findings during the peer review phase, it is unlikely to dislodge current consensus estimates on how much global warming has already occurred – about 1 .2°C, according to many current estimates. compared to the 1.7 degrees postulated by the new study, which is the first instrumental record of pre-industrial ocean temperatures.

“I would like to include more data before claiming a global temperature reconstruction,” said Dr. Hali Kilbourne, a geological oceanographer at the University of Maryland Center for Environmental Sciences. New York Times. With more research undertaken – a Japanese team is studying Okinawan sponges – we may soon have these records.

This article was originally published in Grist has https://grist.org/science/sea-sponges-global-warming/.

Grist is an independent, nonprofit media organization dedicated to telling stories about climate solutions and a just future. Learn more about Grist.org



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