Sea sponges keep climate records and the accounting is grim, new research suggests

If we can rely on sea sponges that track temperatures, climate change is much more advanced than scientists have estimated.

A new study using ocean organisms called sclerosponges to measure Earth’s average temperature suggests the world has already warmed by about 1.7 degrees Celsius over the past 300 years – at least half a degree Celsius more than scientific estimates indicate. consensus as set out in United Nations reports.

The finding, published Monday in the journal Nature Climate Change, is startling, but some scientists say the study authors’ conclusions extrapolated too much about global temperatures than can be confidently inferred from sea sponges.

But the study confronts an important question: How much did the world warm when machines were chugging fossil fuels but people weren’t very organized in measuring temperatures around the world? Scientists say it’s a critical question and something they need to understand better.

The study’s authors say that industrialization before 1900 had a bigger impact than scientists previously realized, that its effect is recorded in the skeletons of ancient sponges, and that the baseline we’ve used to talk about the politics of climate change , was wrong.

“In fact, they show that the industrial age of warming started earlier than we thought, in the 1860s,” Malcolm McCulloch, a lead author of the study and professor of geochemistry at the University of Western Australia, said of the sponges. “The big picture is that the warm-up clock for emissions reductions to minimize the risk of a dangerous climate has been brought forward by at least a decade.”

Scientists not involved in the study said colleagues were grappling with how much warming occurred in the first decades after the Industrial Revolution, but before temperature data became more reliable.

“This is not the only attempt to revisit what we call the pre-industrial baseline and suggest that we may be missing steps in warming in the 19th century,” said Kim Cobb, a paleoclimate and oceanography expert at Brown University and director of the research center. Institute at Brown for Environment and Society. “This is an area of ​​uncertainty and importance.”

The United Nations Intergovernmental Panel on Climate Change (IPCC) estimated in its latest assessment of global warming that global surface temperatures have risen by as much as 1.2 degrees Celsius since pre-industrial times.

Some scientists think the IPCC process – which requires consensus – produces conservative results. For example, scientists who study Earth’s ice have expressed concern that Earth is approaching the ice sheet tipping point sooner than expected and that the IPCC’s sea level rise predictions are far too low.

Cobb, who did not contribute to the Nature Climate Change study, said it would take a tremendous amount of evidence to change what scientists call the pre-industrial baseline, but also that other researchers have found some indications that not enough account is taken into account the warming that occurred before the twentieth century. .

“How large this additional increase in warming actually is remains unknown at this time. Is it important to study this? Could we be missing a few tenths of a degree – yes – that seems to be emerging in the lines of research over the last six to 10 years,” Cobb said.

Sclerosponges are one of many climate proxies that scientists use to gather information about past climate conditions. In sclerosponges, layers of skeletal growth serve a similar purpose to marine biologists, as rings in a tree serve those who work in forests.

Sclerosponges grow slowly and the chemical content of their skeleton changes as they grow, based on their environmental temperature. That means scientists can monitor temperatures by looking at the ratio of strontium to calcium as the creatures grow steadily.

Each half millimeter of growth represents about two years of temperature data, the study said. The creatures can grow for hundreds of years and add layers to their skeletons.

“These are truly unique specimens,” McCulloch said. “The reason we can obtain this unique data is because of the special relationship these animals have with the environment.”

The study authors collected sponges from waters at least 100 feet deep off the coast of Puerto Rico and near the island of St. Croix, analyzed the chemical composition of their skeletons, mapped their findings and compared their data to measurements of sea surface temperature from 1964 to 2012. trends closely aligned.

The sponge skeleton record dates back to 1700, which is longer than reliable human records. That gives scientists a longer reference point to evaluate what temperatures were like before fossil fuels became popular. The researchers believe it outperforms other data sets, some of which were calculated from 19th-century temperature measurements of ships crossing the sea.

The sponge data shows that temperatures began rising in the 1860s – before what is considered by the United Nations Intergovernmental Panel on Climate Change.

However, some outside researchers said the study could make too much of one type of proxy measurement, especially if the data is linked to only one location on Earth.

“People should be careful in assuming that proxies from one part of the Atlantic Ocean will always reflect the global average,” Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, said in an emailed statement, adding that the author’s claims are likely unfounded. “overdone.”

The study authors said they believe the waters off Puerto Rico remain relatively consistent and reflect global changes, just like anywhere else in the world.

The results suggest that humanity has already crossed political guardrails, such as world leaders’ goal of limiting warming to 1.5 degrees Celsius.

Cobb said more work needs to be done with sclerosponges to ensure this work is accurate. And no matter how far we have raised global temperatures, humanity must slow the production of greenhouse gases.

“Every increase in warming brings with it a whole host of larger and worsening climate impacts,” Cobb said. “We are already living with an increase in warming that is not safe. … The job hasn’t changed.”

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