As much as 12 percent of Greenland is melting, according to measurements taken on Monday by scientists with the Danish Meteorological Institute.

It's a record-early start to the continent's ice melting season, triggered by a summertime-like heat wave. Melt season officially begins when at least 10 percent of the island's ice sheet is melting. That happened over the weekend.

At first, researchers thought their observations were a mistake.

"We had to check that our models were still working properly," Peter Langen, a climate scientist at DMI, told the blog Polar Portal.

After checking temperature readings at several research stations, Langen and his colleagues confirmed that even at high altitudes, temps were well above freezing.

"This helped to explain the results," Langen said.

On Monday, as 12 percent of the island melted, thermometers near Kangerlussaq, Greenland, measured 64.4 degrees Fahrenheit -- the warmest April temperature recorded at that location.

The record-setting start to the melt season can mostly be blamed on an unusual pocket of warm, moist air pushed atop Greenland by southerly winds. But the phenomenon is not entirely unexpected. Over the last few decades, Earth's polar climates have experienced dramatic change as a result of man-made global warming.

Temperatures in the arctic have been higher than usual all winter, with air, sea and surface temperatures setting records in December. Sea ice continues to shrink to near-record lows each summer, and earlier this year, the sea ice maximum in the arctic was the smallest in history.

Though the melting ice will likely refreeze in the coming days as cooler temperatures return, melt season will continue in fits and starts as spring turns to summer in Greenland. And each time melting happens, scientists say it makes it easier for melting to begin again.

"Meltwater refreezing releases heat into the snow at depth," explained Jason Box, a scientist with the Geological Survey of Denmark and Greenland, "reducing the amount of heating needed for melt to start and forming ice layers that can help melt water run off the ice sheet earlier with climate warming."