NEW YORK – The loss of sea ice in the Arctic at the end of the 20th century is “unprecedented” in the past 1,450 years in its duration and magnitude, an indication of human-influenced climate change, a study said.

So-called greenhouse gases may be contributing to the warming, and trends from the last several decades suggest there may soon be an ice-free Arctic in the summer, according to a study published Wednesday in the journal Nature.

The ice, which melts every summer before cold weather makes it expand again, shrank this year to its second-smallest size since 1979, according to the U.S. National Snow and Ice Data Center. Although previous sea ice declines have occurred at a similar pace, they don’t match the extent of the melt, the study authors said.

“This drastic and continuous decrease we’ve been seeing from the satellites does seem to be anomalous,” Christophe Kinnard, a study author and a geographer at the Centro de Estudios Avanzados en Zonas Aridas in La Serena, Chile, said.