Researchers studying ancient ice from Canada's Arctic say the samples reveal new information on what climate change could do.
The ice cores were drilled to a depth of a few hundred metres on Ellesmere Island in Nunavut and were saved by an Alberta university when the program that preserved them shut down.
Scientists from the University of Ottawa examined the samples and concluded that temperatures in the early Holocene Epoch between 8,000 and 11,000 years ago were up to five degrees warmer than earlier thought.
That means temperatures not long after the end of the last ice age were warmer than they are now. By examining the effect those temperatures had on the Greenland ice sheet then, the scientists were better able to predict how fast Greenland's current ice cover will melt in the future.
The findings were published Monday in the Proceedings of the National Academy of Sciences.
"If the climate continues to warm -- and the Arctic is warming faster than anywhere else -- then having an event in the past where the temperatures got warmer than today gives us a glimpse of where we might be heading," said geophysics professor Glenn Milne, one of the scientists on the study.
Greenland, along with other melting glaciers, is a major contributor to rising sea levels today. If the melt continues to accelerate, sea levels will jump as well.
Computer models with the new data predict Greenland's ice could lose almost a kilometre of thickness over the next 1,000 years.
The research also determined that the rate of temperature change is the fastest it has been in 12,000 years, bolstering evidence that recent global warming is happening unusually fast and likely caused by human activity.
Previous attempts had been made to pinpoint ancient temperatures, but the two methods produced inconsistent results. One method measured the amount of melted and re-frozen ice in a layer; the second measured isotopes in oxygen in the ice.
The new study manages to get the results from the two methods to match.
David Fisher, another University of Ottawa scientist who worked on the study, said temperatures were warmer in the early Holocene due to a natural variation of the Earth's orbit around the sun and its tilt on its axis.
He said the study had to consider whether the elevation when the ice formed was different, which could have affected the temperature.
The last 50 or 60 years have seen a very sharp temperature increase, but this time, the study says people are the probable culprits.
"You pretty much have to look back 4,000 years, if you look at 25-year averages, you have to go back that far to find temperatures as high as what we've had in the last 25 years," Fisher said.
"And if you look at the last 15 years, you have to go back maybe 8,000 or 9,000 years to find it quite as warm as that."
The ice cores samples, some of which were drilled in the 1980s, had been stored in the Geological Survey of Canada's Ottawa freezers until the program was discontinued about five years ago.
"When we were told we had to disband, we sent out an all-points bulletin, as it were, to any scientists around the world who wanted ice cores," Fisher said.
For a while, he said the cylinders were being stored in commercial freezers along with meat and ice-cream.
The call was answered by the University of Alberta, which accepted them earlier this year.
Some of the collection didn't survive in its new home in Edmonton. A freezer malfunction at the university last month destroyed 12 per cent of the collection.
