Scientists Resolve Temperature 'Paradox' in Greenland Temperatures During Last Ice Age

Scientists have taken a closer look at the ancient past of Greenland to find out a bit more about the landmass's climate. By studying three ice cores, scientists have found that there was warming of the large ice sheet at the end of the last ice age, resolving a long-standing paradox over when the warming occurred.

About 20,000 years ago during the coldest parts of the ice age, large ice sheets covered North America and northern Europe. Global average temperatures were about seven degrees Fahrenheit colder than during pre-industrial times. Then, a shift in Earth's orbit increased the solar energy reaching Greenland and about 18,000 years ago, a release of carbon from the ocean led to a gradual rise in atmospheric carbon dioxide.

Surprisingly, though, analysis of ice cores in the past did not show any warming response as would have been expected from an increase in CO2 and solar energy flux during this time. That's why scientists decided to investigate this particular paradox a bit more closely.

The scientists reconstructed air temperatures by examining ratios of nitrogen isotopes in air trapped within the ice instead of isotopes in the ice itself, which had been used in past studies. In the end, the researchers detected significant warming in response to increasing CO2.

"The Greenland isotope records from the ice itself suggest that temperatures 12,000 years ago during the so-called Younger Dryas period near the end of the ice age were virtually the same in Greenland as they were 18,000 years ago when much of the northern hemisphere was still covered in ice," said Christo Buizert, one of the researchers, in a news release. "But when you reconstruct the temperature history using nitrogen isotope ratios as a proxy for temperature, you get a much different picture. The nitrogen-based temperature record shows that by 12,000 years ago, Greenland temperatures had already warmed by about five degrees (Celsius), very close to what climate models predict should have happened, given the conditions."

The findings reveal a bit more about the ancient climate of Greenland. Not only that, but they show that there was a period of warming as CO2 levels and solar energy increased. This, in turn, shows scientists a bit more about abrupt warming and climate change.

The findings are published in the journal Science.