A handful of centuries-old sponges from deep in the Caribbean are leading some scientists to think that human-caused climate change is starting earlier and warming the world more than they thought.
They calculate that the world has moved beyond the internationally approved goal of limiting global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) since the pre-industrial era, reaching 1.7 degrees Celsius (3.1 degrees Fahrenheit) by 2020. Living sponges — simple animals that filter water — rely on growth records that document changes in water temperature, acidity and carbon dioxide levels in the air, according to a study published Monday in the journal Nature Climate Change.
Other scientists were skeptical of the study’s claim that the world is warming much more than thought. But if the sponge calculations are correct, this would have big consequences, the study’s authors said.
“The big picture is to move the global warming clock forward by at least a decade to reduce emissions to minimize the risk of dangerous climate change,” said the study’s lead author, Malcolm McCulloch, a marine geochemist at the University of Western Australia. “Actually, time is running out.”
“We have ten years less left than we thought,” McCulloch told the Associated Press. “It’s really a diary – what’s the word? – impending disaster.
Over the past few years, scientists have noticed more extreme and damaging weather conditions—floods, storms, droughts, and heat waves—than they expected for the current level of warming. One explanation could be whether there was more warming than scientists initially calculated, said study co-author Amos Winter, a paleooceanographer at Indiana State University. He said the study also supports the theory that climate change is accelerating, put forward last year by former NASA senior scientist James Hansen.
“This is not good news for global climate change because it points to further warming,” said Cornell University climate scientist Natalie Mahowald, who was not part of the study.
Many sponge species are long-lived and record the conditions of their environment in their skeletons as they grow. Scientists have long used sponges in conjunction with other proxies—tree rings, ice cores, and coral—that provide a natural record of changes in the environment over centuries. Doing this helps populate data from before the 20th century.
Winter and McCulloch said that unlike corals, tree rings and ice cores, sponges allow water to flow from anywhere and thus can record a broader range of ecological change.
They used measurements from a rare type of small, hard-shelled sponge to create a temperature record from the 1800s; this record differed greatly from the scientifically accepted versions used by the United Nations Intergovernmental Panel on Climate Change. The study finds that the mid-1800s were about half a degree Celsius cooler than previously thought, and that warming from heat-trapping gases began about 80 years earlier than measurements used by the IPCC. IPCC figures show that warming began just after 1900.
McCulloch and Winter said it makes sense that warming started earlier than the IPCC says because the Industrial Revolution began in the mid-1800s and carbon dioxide was spewed into the air. Scientists have found that carbon dioxide and other gases from burning fossil fuels cause climate change.
Winter and McCulloch said these rusty orange long-lived sponges — one of them was more than 320 years old when collected — were special enough to make them an ideal measuring tool, better than those scientists used in the mid-to-late period. 1800s.
“These are cathedrals of history, of human history, recording carbon dioxide in the atmosphere, temperature and pH of water,” Winter said.
“They are very beautiful,” he said. “These are not easy to find. You need a special team of divers to find them.”
That’s because they live in darkness at depths of 100 to 300 feet (33 to 98 meters), Winter said.
The IPCC and most scientists use temperature data from ships from the mid-1800s that measured temperatures by lowering wooden buckets to submerge crews. Some of these measurements may be skewed depending on how the summation is done; for example, as water collects near a hot steamship engine. But sponges are more accurate because scientists can regularly track tiny deposits of calcium and strontium in the creatures’ skeletons. Warmer water will lead to more strontium compared to calcium, and colder water will lead to a higher percentage of calcium compared to strontium, Winter said.
University of Pennsylvania climate scientist Michael Mann, who was not part of the study, has long opposed the IPCC baseline and thinks warming started earlier. But he was still skeptical of the study’s findings.
“In my view, it would be naive to claim that instrumental records based on paleosponges from one part of the world are wrong. Frankly, it doesn’t make any sense to me,” Mann said.
At a news briefing, Winter and McCulloch repeatedly defended the use of sponges as an accurate indicator of world temperature changes. They said that except for the 1800s, temperature reconstructions based on sponges matched global records from instruments and other proxies such as coral, ice cores and tree rings.
Although these sponges are only found in the Caribbean, they are a good proxy for the rest of the world because they are at a depth that is not affected as much by the hot and cold cycles of El Niño and La, McCulloch and Winter said. Nina’s water matches well with global ocean temperatures, McCulloch and Winter said.
Princeton University climate scientist Michael Oppenheimer (who was also not part of the sponge study) said that even if the McCulloch team was right about a colder baseline in the 1800s, that shouldn’t really change the danger levels scientists identified in their report. That’s because danger levels “do not depend on the absolute value of pre-industrial temperatures,” he said, but rather on how much temperatures have changed since then.
Although the study found warming since the pre-industrial era was halted at 1.7 degrees Celsius (3.1 Fahrenheit) in 2020, a record warm 2023 pushed that to 1.8 degrees (3.2 Fahrenheit), McCulloch said.
“The pace of change is much faster than we thought,” McCulloch said. “We are heading towards very dangerous, high-risk scenarios for the future. And the only way to stop this is to reduce emissions. Urgently. It’s very urgent.”
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Teresa de Miguel contributed to this report from Mexico City.
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