Scientists have been struggling to explain why warming has led to sea ice shrinking in the arctic, while it has actually spread in the Antarctic, and is now thought   to be caused by relatively cold plumes of fresh water derived from melting beneath the Antarctic ice shelves, , according to a scientific study in the journal Nature Geoscience.

"The paradox is that global warming leads to more cooling and more sea ice around Antarctica," Richard Bintanja, a climate researcher at the Royal Netherlands Meteorological Institute in Utrecht, told Nature. The cool surface waters then re-freeze more easily during the Fall and Winter.

"We found a significant increase in the length of the melting season at most of the stations with the longest temperature records," said study author Nick Barrand, in a statement. "At one station, the average length of the melt season almost doubled between 1948 and 2011."

This melt water has a relatively low density, so it accumulates in the top layer of the ocean.

The researchers analyzed satellite data and buoy observations for how much salt was in the water and how warm it was for the period 1985 to 2010, they then compared that data to the output of a global climate model that simulated how loosing 250 gigatones of meltwater from the Antarctic ice sheet each year would affect conditions.

Climate scientists have been intrigued as to why the Antarctic sea ice shows a small but statistically significant expansion of about 1.9 percent per decade since 1985, while sea ice in the Arctic has been shrinking over past decades.

"We found that the model was very good at reproducing the pattern and timing of the melt, and changes in melting between years," Barrand said. "This increases confidence in the use of climate models to predict future changes to snow and ice cover in the Antarctic Peninsula."