Arctic sea ice melted less this summer and continued to cover a greater expanse than last year's record minimum, NASA data shows.

Following unusually cold summer temperatures in the northernmost latitudes, the US space agency said Friday that the sea ice extent shrunk to 1.97 million square miles (5.10 million square kilometers).

The analysis was based on September 13 data by NASA and the NASA-supported National Snow and Ice Data Center (NSIDC) at the University of Colorado in Boulder.

On September 16, 2012, Arctic sea ice shrunk to its smallest surface ever recorded by satellite at 1.32 million square miles, about half the size of the average minimum in the previous two decades.

Over the long term, Arctic sea ice surface has dropped 12 percent per decade since the end of the 1970s, a decline that accelerated after 2007, according to the NSIDC.

"I was expecting that this year would be higher than last year," said Walt Meier, a glaciologist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

"There is always a tendency to have an uptick after an extreme low; in our satellite data, the Arctic sea ice has never set record low minimums in consecutive years."

But the remaining Arctic sea ice cover is much thinner overall compared to the previous decades by as much as 50 percent. Scientists say thinner seasonal ice is replacing older, thicker ice as it melts away.

"Thinner ice melts completely at a faster rate than thicker ice does, so if the average thickness of Arctic sea ice goes down, it's more likely that the extent of the summer ice will go down as well," said Goddard senior scientist Joey Comiso.

"At the rate we're observing this decline, it's very likely that the Arctic's summer sea ice will completely disappear within this century."