Rising levels of carbon dioxide really did bring about the end of the most recent ice age, say researchers. By compiling a global climate record, a team has shown that regions in which concentrations of greenhouse gases increased after the warming were exceptions to the big picture.
There are many ideas about what caused the end of the last ice age 10,000 years ago, but a lack of data has hindered testing of hypotheses. It has been known that changes in temperature and CO2 levels were closely correlated during this time, but no one has been able to prove that CO2 caused the warming.
Ice samples from Antarctica even suggested that temperatures rose a few centuries before CO2 levels, making it impossible for the gas to have been responsible. This provided ammunition for climate sceptics.
But, by analysing data gathered from 80 locations around the world, Jeremy Shakun, a palaeoclimatologist at Harvard University in Cambridge, Massachusetts, and his colleagues have shown that at the global level, warming followed CO2 increases. The team used seven different records of past temperature, including ice cores, ancient pollen and the chemical composition of fossilized microscopic life.
“This is the first effort to get most of the data that’s out there together,” says Shakun. “It's the first hard empirical proof that CO2 was a big driver of global warming out of the ice age.”