by A handful of centuries-old sponges from deep in the Caribbean are making some scientists think that human-caused climate change started earlier and that the world is warmer than they thought.
They calculate that the world has already exceeded the internationally agreed goal of limiting global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) from pre-industrial times, hitting 1.7 degrees (3.1 degrees Fahrenheit) from 2020. They analyzed on six of the long stages of living sponges – simple water-filtering animals – for growth records that document changes in water temperature, acidity and carbon dioxide levels in the air, according to a study in Monday’s journal Nature Climate Change.
Other scientists were skeptical of the study’s claim that the world had warmed much more than thought. But if the sponge calculations are correct, there are big consequences, the study authors said.
“The big picture is that the global warming clock for emissions reductions to minimize the risk of dangerous climate change has been turned forward by at least a decade,” study author Malcolm McCulloch, a marine geochemist at the University of Western Australia . “Basically, time is running out.”
“Ten years is less than we thought,” McCulloch told the Associated Press. “It’s actually a diary – what’s the word? — an impending disaster.”
Over the past several years, scientists have observed more extreme and damaging weather – floods, storms, droughts and heat waves – than they expected for the current level of warming. One explanation for that is if there was more warming than scientists had originally calculated, said study co-author Amos Winter, a paleo-oceanologist at Indiana State University. He said this study also supports the theory that climate change is accelerating, proposed by former NASA top scientist James Hansen last year.
“This is not good news for global climate change because it means more warming,” said Cornell University climate scientist Natalie Mahowald, who was not part of the study.
Many sponge species are long-lived, and as they grow they record the environmental conditions around them in their skeleton. Scientists have long used sponges along with other proxies – tree rings, ice cores and corals – that naturally display a record of changes in the environment over centuries. That helps to fill in data before the 20th century.
Sponges — unlike corals, tree rings and ice cores — get water flowing from all around them 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 1800s that differs significantly from the scientifically accepted versions used by the United Nations’ Intergovernmental Panel on Climate Change. The study found that the mid-1800s were about half a degree Celsius cooler than previously thought, with warming from heat-trapping gases kicking in about 80 years earlier than the measurements used by the IPCC. IPCC figures show that warming was kicking in just after 1900.
It makes sense that the warming started earlier than the IPCC says because the Industrial Revolution had begun by the mid-1800s and carbon dioxide was being pumped into the air, McCulloch and Winter said. Climate change is caused by carbon dioxide and other gases from burning fossil fuels, according to scientists.
Winter and McCulloch said these long rusty orange sponges – one of which was more than 320 years old when collected – are special in a way that makes them an ideal measuring tool, better than what scientists have used from mid to late. 1800s.
“They are cathedrals of history, of human history, recording atmospheric carbon dioxide, water temperature and water pH,” Winter said.
“They are beautiful,” he said. “It’s not easy to find them. You need a special team of divers to find them.”
That’s because they live 100 to 300 feet deep (33 meters to 98 meters) in the dark, Winter said.
The IPCC and most scientists use temperature data for the mid-1800s that came from ships whose crews would take temperature readings by lowering wooden buckets to submerge them in water. Some of these measurements may be biased depending on how the collection was done — for example, if the water is collected near a hot steam engine. But the sponges are more accurate because scientists can trace regular tiny deposits of calcium and strontium on the crustaceans’ skeletons. More strontium relative to calcium would result in warmer water, while higher proportions of calcium relative to strontium would result in cooler water, Winter said.
University of Pennsylvania climate scientist Michael Mann, 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 results of the study.
“In my opinion, it is naive to claim that the instrumental record is wrong based on paleosponges from one region of the world. It honestly makes no sense to me,” Mann said.
In a briefing, Winter and McCulloch repeatedly defended the use of sponges as an accurate proxy for global temperature changes. They said that except for the 1800s, their temperature reconstruction based on sponges matches global records from instruments and other proxies such as corals, ice cores and tree rings.
And although these sponges are only found in the Caribbean, McCulloch and Winter said they are a good indicator for the rest of the world because they are at depths that are not affected too much by the hot and cold cycles of El Nino and La. Nina, and the water is in good agreement 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 cooler baseline in the 1800s the danger levels set by the scientists in their reports should not really change . That’s because the danger levels were “not tied to the absolute value of pre-industrial temperatures” but more to how much temperatures have changed since then, he said.
While the study stopped at 2020 at 1.7 degrees Celsius (3.1 degrees Fahrenheit) in warming from pre-industrial times, the warm 2023 record pushes that up to 1.8 degrees (3.2 degrees Fahrenheit), McCulloch said.
“The rate of change has been much faster than we thought,” McCulloch said. “We are entering high risk and dangerous situations for the future. And the only way to stop this is to reduce emissions. Urgently. It is urgent.”
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Teresa de Miguel contributed to this report from Mexico City.
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Read more about AP’s climate coverage at http://www.apnews.com/climate-and-environment
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Follow Seth Borenstein on X at @borenbears
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