Ocean sponges suggest that the Earth has warmed for longer, more than thought; some scientists have doubts

A handful of ancient sponges from deep in the Caribbean are leading some scientists to think that human-induced climate change may have started earlier and warmed the world more than they thought.

They calculate that the world has already surpassed the internationally agreed goal of limiting global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) since pre-industrial times, and 1.7 degrees (3 .1 degrees Fahrenheit). They analyzed six of the long-term developments. -living sponges – simple animals that filter water – for growth data documenting changes in water temperature, acidity and carbon dioxide levels in the air, according to a study in the journal Nature Climate Change on Monday.

Other scientists were skeptical of the study’s claim that the world has warmed so much more than thought. But if the sponge calculations are correct, there are major consequences, according to the study authors.

“The big picture is that the warming clock on emissions reductions to minimize the risk of dangerous climate changes is brought forward by at least a decade,” said lead author Malcolm McCulloch, a marine geochemist at the University of Western Australia. “In fact, time is running out.”

“We have 10 years less than we thought,” McCulloch told The Associated Press. ‘It’s basically a diary of – what’s the word? – impending disaster.”

In recent years, scientists have noticed more extreme and damaging weather events – floods, storms, droughts and heat waves – than they expected at current levels of warming. One explanation for this would be that there would be more warming than scientists initially calculated, said co-author Amos Winter, a paleoceanographer at Indiana State University. He said this study also supports the theory that climate change is accelerating, proposed last year by former top NASA scientist James Hansen.

“This is not good news for global climate change because it implies further warming,” said climate scientist Natalie Mahowald of Cornell University, who was not part of the study.

Many sponge species are long-lived and as they grow they record the conditions of the environment around them in their skeletons. Scientists have long used sponges along with other proxies – tree rings, ice cores and coral – that naturally show environmental changes over centuries. This helps fill in data from before the 20th century.

Sponges – unlike coral, tree rings and ice cores – allow water to flow through them from anywhere, so they can record a larger area of ​​ecological change, Winter and McCulloch said.

They used measurements from a rare species of small and hard sponges to create a temperature record for the 19th century that differs sharply from the scientifically accepted versions used by the United Nations Intergovernmental Panel on Climate Change. The research shows that the mid-19th century was about half a degree Celsius cooler than previously thought, with warming from heat-trapping gases starting about 80 years earlier than the measurements used by the IPCC. Figures from the IPCC show that warming started just after 1900.

It makes sense that warming started earlier than the IPCC says, because by the mid-19th century the Industrial Revolution had begun and carbon dioxide was spewing into the air, McCulloch and Winter said. Carbon dioxide and other gases released from the burning of fossil fuels are causing climate change, scientists have found.

Winter and McCulloch said these rusty, orange, long-lived sponges — one was more than 320 years old when it was collected — are special in a way that makes them an ideal measuring tool, better than what scientists were using in the mid-to-late 1900s. 19th century.

“They are cathedrals of history, of human history, recording carbon dioxide in the atmosphere, the temperature of the water and the pH of the water,” Winter said.

“They’re beautiful,” he said. “They are not easy to find. You need a special team of divers to find them.”

That’s because they live 100 to 300 feet deep (33 to 98 meters) in the dark, Winter said.

The IPCC and most scientists use temperature data from the mid-19th century that come from ships whose crews took temperature measurements by lowering wooden buckets to dip water to the top. Some of those measurements may be biased depending on how the collection is done, for example if the water is collected near a warm steamship engine. But the sponges are more accurate because scientists can track regular small deposits of calcium and strontium on the creatures’ skeletons. Warmer water would lead to more strontium compared to calcium, and cooler water would lead to higher amounts of calcium compared to strontium, Winter said.

Climate scientist Michael Mann of the University of Pennsylvania, who was not part of the study, has long disagreed with the IPCC’s baseline and thinks warming started earlier. But he was still skeptical about the study’s findings.

“In my opinion, it beggars credulity to claim that the instrumental record is wrong based on paleosponges from one region of the world. I honestly don’t think it makes any sense,” Mann said.

In a news briefing, Winter and McCulloch repeatedly defended the use of sponges as an accurate measure of changes in global temperature. They said that, with the exception of the 19th century, their temperature reconstruction from sponges matches global data from instruments and other proxies such as coral, ice cores and tree rings.

And while these sponges are only in the Caribbean, McCulloch and Winter said they are a good representation for the rest of the world because they are at a depth that isn’t too affected by the warm and cold cycles of El Nino and La Nina, and the water matches global ocean temperatures well, McCulloch and Winter said.

Climate scientist Michael Oppenheimer of Princeton University, who was also not part of the sponge study, said that even if the McCulloch team is right about a cooler baseline in the 19th century, it shouldn’t really change the danger levels scientists identified in their reports . That’s because the hazard levels were “not tied to the absolute value of pre-industrial temperatures,” but rather to the extent to which temperatures changed from that time, he said.

Although the study stopped short in 2020 at 1.7 degrees Celsius (3.1 degrees Fahrenheit) of warming since pre-industrial times, a record warm 2023 pushes that up to 1.8 degrees (3.2 degrees 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. Most urgent.”


Teresa de Miguel contributed to this report from Mexico City.


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