Scientists have resolved a controversial but key climate change mystery, bolstering climate models and confirming that Earth is hotter than it's been in at least 12,000 years, and perhaps even the last 128,000 years, according to the most recent annual global temperature data.
This mystery is known as the "Holocene temperature conundrum," and it describes a debate that has gone on over how temperatures have changed during the Holocene, an epoch that describes the last 11,700 years of our planet's history. While some previous proxy reconstructions suggest that average Holocene temperatures peaked between 6,000 and 10,000 years ago and the planet cooled after this, climate models suggest that global temperatures have actually risen over the past 12,000 years, with the help of factors like rising greenhouse gas emissions and climate change.
This "conundrum" has "cast doubts among skeptics about the efficacy of current climate models to accurately predict our future," lead author Samantha Bova, a postdoctoral researcher associate at Rutgers University, told Space.com in an email.
The new research puts this uncertainty to rest, however, demonstrating that current climate projections are right on the money.
The study "eliminates any doubts about the key role of carbon dioxide in global warming and confirms climate model simulations that show global mean annual temperature warming, rather than cooling, across the Holocene period," Bova said.
Specifically, the team demonstrated "that late Holocene cooling as reconstructed by proxies is a seasonal signal," Bova told Space.com.
To do this, the team developed a new method that allowed them to "use seasonal temperatures to come up with annual averages. Using our new method, we demonstrate that Holocene mean annual temperatures have been steadily rising," Bova added.
The scientists analyzed previously published sea surface temperature data, which used information about the fossils of foraminifera — single-celled organisms that live on the surface of the ocean —and other biomarkers from marine algae. This allowed them to reconstruct temperatures through history.
With this data, "we show that the post-industrial increase in global temperature rose from the warmest mean annual temperature recorded over the past 12,000 years," Bova said, adding that this is contrary to recent research. "Earth’s global temperatures have therefore reached uncharted territory that has not been observed over at least the past 12,000 and perhaps the past 128,000 years."
"Given that 2020 is tied for the warmest year on record based on the new NASA/NOAA data release, our results demonstrate that average annual temperatures in 2020 were the warmest of the last 12,000 years and possibly the last 128,000 years," Bova concluded. (NOAA is the U.S. National Oceanic and Atmospheric Administration.)
By confirming temperature records throughout this time period, the team didn't just provide additional evidence for "the efficacy of current climate models in accurately simulating climate over the past 12,000 years," Bova said. The work also "gives confidence in their ability to predict the future."
This work was published Jan. 27 in the journal Nature.
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