Chemical records written on marine sponge skeletons suggest that as early as 2010 we surpassed the critical threshold of 1.5°C of warming. If true, this puts us close to – or even at – approximately 2°C today.
Being ahead of schedule would explain why such extreme climate consequences have been affecting us much earlier than expected. Last year’s huge jumps in temperatures left researchers stunned and searching for theories to explain some mysterious missing factor to explain things.
“The differences are quite profound,” geochemist Malcolm McCulloch of the University of Western Australia said at a news conference. “There’s no really strong evidence that we’re on a serious path to reducing emissions. That’s the most worrying thing.”
– John Gibbons (@think_or_swim) July 21, 2023
McCulloch and his colleagues used sea sponges as a kind of natural thermometer, to look back in time, long before humanity’s industrial age, into a deeper layer of our ocean than previous measurements.
The skeletons of sea sponges store different proportions of strontium compared to calcium depending on the temperature of the water in which they grow. These animals grow very slowly, approximately only 0.2 mm per year, which, given the size of some individuals, implies that they could be up to 5,000 years old.
The sponges used by the researchers (Ceratoporella nicolsoni) are found 60 meters (197 ft) deep in a mixed layer of ocean in the Caribbean. This depth, while still influenced by atmospheric warming, dampens the extreme fluctuations experienced closer to the surface, providing a better indication of overall average temperatures.
What’s more, this area is known to track global temperatures closely and is less influenced by natural fluctuations like ENSO than other ocean regions.
The researchers used about half a dozen sponges, estimated to be between 300 and 400 years old, giving the researchers an approximate temperature dating back to the 18th century.
“The new research shows that human-caused global warming began as early as the 1860s, several decades earlier than previously thought,” says climatologist Georgy Falster of the Australian National University, who was not involved in the study.
“Correcting for early global warming, we have already surpassed the 2015 Paris Agreement threshold of 1.5° above pre-industrial global temperature, and are on track to surpass 2° of warming by the end of the decade.” of 2020″.
McCulloch believes that all the strange weather we’ve been experiencing, including massive heatwaves in Europe in regions that don’t normally have them, are what we’d expect with around 2°C of post-industrial warming.
Ice-free summers in the polar oceans are also expected to begin around a 2° threshold. We are rapidly approaching that point.
— Dr. Ella Gilbert (@Dr_Gilbz) January 19, 2024
“A single new paleo record off the coast of Puerto Rico is a valuable addition to the large body of evidence of warming,” warns climatologist Malte Meinshausen of the University of Melbourne, who was not involved in the study. “But it’s just that, one study among hundreds.”
McCulloch and his team are interested in replicating their study in other oceans and have been trying to do so for years. However, other substitutes they have tried to use, such as corals, have not provided the same level of precision. Locating more of these deeper-water sponges in the midst of the vast oceans has proven a challenge.
But McCulloch is confident that his data on sea sponges fit the observed data better than the sea surface measurements we have relied on until now. It is more similar to CO2 records the IPCC average and also correlates with known historical geological events, such as past volcanic eruptions.
Previous models, including the IPCC, calibrated their data using measurements taken from ships since the 1920s. At first, these measurements were not very systematic, often lacked data from the southern hemisphere, and contained a number of anomalies that have not yet been identified. have completely explained, such as the inexplicable cooling during the 20th century only of the ocean but not of the land.
This conflict is not present in the marine sponge data.
The new data set “appears to be well correlated with global surface temperature trends,” agrees Australian National University climatologist Mark Howden, who was not involved in the study. “He shows that the warming of the industrial era began in the mid-1860s, similar to previous research.”
Their results also contribute to the ongoing debate among climate scientists about whether the rate of warming has been increasing. Data from marine sponges show a strong signal of an increasing rate of warming.
“In my opinion, based on our results, the climate change clock has been turned forward by about a decade,” explains McCulloch. “So things that we thought would have happened 10 years from now are actually happening now and emissions are still very high. Unless we start reducing them, these things are going to get progressively worse.”
McCulloch believes it is still possible to keep warming at just over 2°, which would be much safer than the 5° we are currently heading for on land.
“Talking about 1.5° or 2° is to some extent irrelevant,” McCulloch insists, explaining that targets should focus on reduced amounts of fossil fuels, not temperature thresholds.
“Each additional increase in warming will make the results worse. We have to shift our focus toward reductions. That’s the key.”
This study was published in Nature Climate Change.