March 1, 2024

Ocean sponges suggest Earth has been warming for longer than previously thought; some scientists doubt

A handful of centuries-old sponges from the depths of the Caribbean are leading some scientists to think that human-caused climate change started earlier and has warmed the world more than they thought.

They calculate that the world has already surpassed the internationally approved target of limiting global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) since pre-industrial times, reaching 1.7 degrees (3.1 degrees Fahrenheit) in 2020. They analyzed six of the long-lived sponges — simple animals that filter water — for growth records that document changes in water temperature, acidity and carbon dioxide levels in the air, according to a study published in the journal Nature. Monday’s Climate Change.

Other scientists were skeptical of the study’s claim that the world has warmed much more than previously thought. But if the sponge’s calculations are correct, there will be major repercussions, the study authors said.

“The big picture is that the global warming clock for reducing emissions to minimize the risk of dangerous climate change is being moved forward by at least a decade,” said study lead author Malcolm McCulloch, a marine geochemist at the University of Australia. Western. “Basically, time is running out.”

“We have a decade less than we thought,” McCulloch told the Associated Press. “It’s really a diary of…what’s the word? – imminent disaster.”

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

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

Sponges — unlike corals, tree rings and ice cores — cause water to flow everywhere, so they can record a larger area of ​​ecological change, Winter and McCulloch said.

They used measurements from a rare species of small, hard-shelled sponges to create a temperature record for the 19th century that differs greatly from the scientifically accepted versions used by the United Nations’ Intergovernmental Panel on Climate Change. The study concludes that the mid-1800s was about half a degree Celsius colder than previously thought, with warming caused by heat-trapping gases emerging about 80 years before the measurements used by the IPCC. IPCC figures show that warming began shortly after 1900.

It makes sense that warming started earlier than the IPCC claims, because by the mid-1800s the Industrial Revolution had begun and carbon dioxide was being spewed into the atmosphere, McCulloch and Winter said. Carbon dioxide and other gases from the burning of fossil fuels are causing climate change, scientists have established.

Winter and McCulloch said these long-lived, rusty orange sponges — one of them 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 used in the mid to late 2000s. afternoon. 1800.

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

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

That’s because they live 33 to 98 meters deep in the dark, Winter said.

The IPCC and most scientists use mid-19th century temperature data from ships whose crews took temperature readings by lowering wooden buckets into the water. Some of these measurements may be skewed depending on how the collection was made – for example, if the water was collected near a hot steamship engine. But sponges are more accurate because scientists can track small, regular deposits of calcium and strontium in the creatures’ skeletons. Warmer water would lead to more strontium compared to calcium, and colder water would lead to higher proportions of calcium compared to strontium, Winter said.

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

“In my opinion, it requires credulity to claim that the instrumental record is wrong based on paleo-sponges from one region of the world. It honestly doesn’t make sense to me,” Mann said.

At a press conference, Winter and McCulloch repeatedly defended the use of sponges as an accurate indicator of changes in the world’s temperature. They said that, with the exception of 1800, the sponge-based temperature reconstruction matches global instrument records and other indicators such as corals, ice cores and tree rings.

And even though 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 is not greatly affected by the hot and cold cycles of El Nino and La Nina, and the water it 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 McCulloch’s team is right about a colder baseline in 1800, that shouldn’t actually change danger levels. that scientists have established in their reports. This is because danger levels were “not linked to the absolute value of pre-industrial temperatures” but rather to how much temperatures have changed since then, he said.

Although the study stopped in 2020, with 1.7 degrees Celsius (3.1 degrees Fahrenheit) of warming since pre-industrial times, record heat in 2023 brings that figure to 1.8 degrees (3.2 degrees Fahrenheit) , McCulloch said.

“The rate 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. With much urgency.


Teresa de Miguel contributed to this report from Mexico City.


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