Stationary sea sponges are sparking debate in the climate science world with new research into the underwater creatures suggesting the planet could be a lot hotter than we thought.
The world’s nations have been committed for the past decade to keeping global warming well under an average 2 degrees Celsius increase, compared with temperatures before the Industrial Revolution.
But establishing exactly what temperatures were in the pre-industrial 1700s has been difficult.
Now scientists behind a new paper in Nature Climate Change say they have an answer.
They found that Caribbean sea sponge skeletons have effectively recorded temperatures for about 300 years, giving us an idea of both past and future temperatures.
The findings, based off six samples of the sclerosponge species Ceratoporella nicholsoni from Puerto Rico, suggest the planet may already be 1.7C warmer, based on the average surface temperature of both the ocean and land.
This is half a degree higher than the recent 10-year average of 1.2 C of warming reported by the World Meteorological Organisation since pre-industrial times.
The 1.7C of warming reported in the new research would put Earth beyond the preferred international policy of limiting the temperature increase to 1.5C.
And the researchers behind the sponge work warn the world could be on track to 2C of warming by the end of this decade.
What makes a sponge a thermometer?
About 10 years ago one of the study’s authors Professor Malcolm McCulloch, a coral reef geochemistry expert from the University of Western Australia, was looking into ocean acidification.
Thinking sclerosponges from Puerto Rico could be a good collection to investigate, he got in contact with Indiana State University oceanography and palaeoclimatology scientist Professor Amos Winter.
Every year the sclerosponges lay down about 0.25 millimetres of calcified skeleton.
“They calcify differently from corals in that these sponges tend to pump a lot of seawater through their tissue and extract particulates to feed on,” Professor McCulloch said.
“The sclerosponges are unique … and don’t seem to manipulate the calcifying environment too much. So they’re pretty much a direct record of the ambient seawater.”
