Has Earth Warmed More Than We Thought?

By Gregory Stachel
08 February 2024

Old sponges from deep in the Caribbean Sea are causing some researchers to think human-caused climate change began sooner than scientists have thought. But, if a recent study is correct, world temperatures are increasing faster than United Nations' estimates suggest.

The researchers from American and Australian universities published their sponge findings recently in Nature Climate Change. They said, if their findings are correct, the world has already gone past a temperature limit set by international negotiators. Negotiators of the Paris Agreement on climate change set 1.5 degrees Celsius as a limit for the increase of the world's temperature from pre-industrial times. Pre-industrial times are from about 1850 to 1900. But the American and Australian researchers said that the world hit a 1.7-degree Celsius increase in 2020.

The scientists looked at six special sponges that are known to live hundreds of years. They examined the sponges' growth records to find very small levels of the elements calcium and strontium. The scientists said that the amount of calcium and strontium changes, depending on the water temperature.

Malcolm McCulloch is an ocean scientist at the University of Western Australia. He was the lead writer of the study. McCulloch noted that the currently accepted temperature estimates for the 1850-1900 period were too high. That means that present-day temperature increases are larger and the Earth's temperature is warming faster than scientists have believed. He said, "We have a decade less than we thought."

In the past several years, many scientists have noted that there seems to be more extreme weather than they had expected. One explanation would be that the Earth is warming faster than scientists had first believed, said Amos Winter.

Winter helped write the study. He is an ocean scientist at Indiana State University. He said the study supports the theory that climate change is quickening. Former top NASA scientist James Hansen also has proposed that theory.

Sponges get water flowing from all over them so they can record a larger area of environmental change, Winter and McCulloch said. The research team examined sponges that lived in a special "mixed" area of the ocean that is 33 to 91 meters deep. The researchers were able to estimate nearly the exact atmospheric temperature of the Earth from the amount of calcium and strontium in the deep-sea sponges.

Their results were different from the scientifically accepted temperature estimates used by the United Nations' Intergovernmental Panel on Climate Change (IPCC). The IPCC temperature estimates are the basis for the U.N. temperature goals.

The Nature Climate Change study finds that the mid-1800s were about half a degree Celsius cooler than believed. It also found that warming from heat-trapping gases started about 80 years earlier than the measurements the IPCC uses. IPCC numbers show warming started just after 1900.

McCulloch and Winter said it makes sense that the warming started earlier than the IPCC stated because by the mid-1800s industries had begun polluting the air with carbon dioxide.

For pre-industrial temperatures, the IPCC and most scientists use data that came from ships whose crews would take the temperature of water near the surface. Some of the measurements could change based on how the collection was done.

The researchers said sponges provide better information because of the way they store chemical elements in their skeletons. When waters are warmer, there is more of the element strontium and less of the mineral calcium, Winter said.

University of Pennsylvania climate scientist Michael Mann, who was not part of the study, has thought warming started before the IPCC said it did. But he doubted the study's findings.

"In my view it begs credulity to claim that the instrumental record is wrong based on paleo-sponges from one region of the world," Mann said.

But Winter and McCulloch have defended their use of sponges to identify world temperature change. They said, except for the 1800s, their temperature findings based on sponges follow global records from other devices. These include scientific instruments and measurements from things like coral, ice, and tree rings.

Princeton University climate scientist Michael Oppenheimer was not part of the sponge study either. He said, even if the McCulloch team is right, it should not change warnings from scientists. He said that the danger level is not tied to the exact "value of preindustrial temperatures."

McCulloch added that "...the only way to stop this is to reduce emissions. Urgently. Most Urgently.

I'm Gena Bennett. And I'm Gregory Stachel.

Gregory Stachel adapted this Associated Press story by Seth Borenstein for VOA Learning English.

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Words in This Story

sponge – n. a type of sea animal from which natural sponges are made

decade – n. a period of 10 years

beg – v. to cause someone to ask a specified question as a reaction or response

credulity – n. ability or willingness to believe something

paleo- – prefix connected with ancient times

region – n. a part of a country or of the world that is different or separate from other parts in some way

emission – n. a gas, such as carbon dioxide, that is sent out or produced by a process like burning