New research suggests Arctic sea ice is thinning more rapidly than we thought it was.

Researchers combined modern and historical ice measurements to determine how it has changed over time, the University of Washington reported. The findings showed the central Arctic Ocean experienced ice thinning of about 65 percent between the years of 1975 and 2012. During this same time period September ice thickness (when ice cover is at its minimum) was 85 percent thinner.

"The ice is thinning dramatically," said lead author Ron Lindsay, a climatologist at the UW Applied Physics Laboratory. "We knew the ice was thinning, but we now have additional confirmation on how fast, and we can see that it's not slowing down."

The study is the first to combine all available observations of Arctic sea ice thickness, and highlights how much the climate has really changed in recent decades.

"A number of researchers were lamenting the fact that there were many thickness observations of sea ice, but they were scattered in different databases and were in many different formats," Lindsay said.

The study looked at data from under-ice submarines gathered between 1975 and 1990 as well as from the NASA IceSat satellite operated from 2003 to 2008, IceBridge aircraft-based measurements, under-ice moored observations in the Beaufort Sea from the Woods Hole Oceanographic Institution, and several other measurement methods. In the past critics have said the UW group's calculations on sea ice loss (that combine weather data, sea-surface temperatures and satellite measurements ) are too rapid, but these new findings suggest the ice is thinning even more rapidly than those past models had suggested.

"At least for the central Arctic basin, even our most drastic thinning estimate was slower than measured by these observations," said co-author Axel Schweiger, a polar scientist at the UW Applied Physics Laboratory.

The recent study also backs up the methods that used physical processes to calculate monthly ice volume.

"Using all these different observations that have been collected over time, it pretty much verifies the trend that we have from the model for the past 13 years, though our estimate of thinning compared to previous decades may have been a little slow," Schweiger said.

The year 2012 summer sea ice levels were observed to reach an all-time low, but the following two years have seen a small increase.

"What we see now is a little above the trend, but it's not inconsistent with it in any way," Lindsay said. "It's well within the natural variability around the long-term trend."

The findings were published in a recent edition of The Cryosphere and was funded in part by the National Science Foundation and NASA.