Researchers have long known a large volcano erupted somewhere in the world around that time causing a global cool-down, but they didn't know exactly where or when.
Now Franck Lavigne, a geoscientist at Pantheon-Sorbonne University's Laboratory of Physical Geography in Meudon, France, has offered data and close-up photographs of the remains of what he says is the guilty volcano at a conference on volcanism and the atmosphere in Iceland.
But he would not reveal the name of the specific volcano, saying he had agreed with his research colleagues not to identify it until the work is published in a peer-reviewed journal, ScienceNews.org reported
Most volcanologists at the conference said they suspected the pictures were likely of an Indonesian volcano, but Lavigne is remaining mum for the moment.
Ice cores from Greenland and Antarctica dating to the 13th century contain huge amounts of sulfur, and tree rings, historical records and other evidence suggest the planet cooled soon thereafter.
Lavigne said geochemical analyses of rocks from his mystery volcano matched the chemistry of the polar sulfur almost perfectly.
"We think the eruption may have been in the late spring or summer of 1257," he said.
Many scientists say they remain to be convinced and will await the publication of Lavigne's findings.