The recent loss of sea ice in the Arctic is greater than any natural variation in the past 1½ millennia, a Canadian study shows.

"The recent sea ice decline … appears to be unprecedented," said Christian Zdanowicz, a glaciologist at Natural Resources Canada, who co-led the study and is a co-author of the paper published Wednesday online in Nature.

"We kind of have to conclude that there's a strong chance that there's a human influence embedded in that signal."

In September, Germany's University of Bremen reported that sea ice had hit a record low, based on data from a Japanese sensor on NASA's Aqua satellite. The U.S. National Snow and Ice Data Center, using a different satellite data set, reported that the sea ice coverage in 2011 was the second-lowest on record, after the record set in 2007.

What makes recent sea ice declines unique is that they have been driven by multiple factors that never all coincided in historical periods of major sea ice loss, said Christophe Kinnard, lead author of the new report.

"Everything is trending up – surface temperature, the atmosphere is warming, and it seems also that the ocean is warming and there is more warm and saline water that makes it into the Arctic," Kinnard said, "and so the sea ice is eroded from below and melting from the top."