New study includes data from the pre-satellite era
FRISCO — After analyzing data from multiple sources, scientists say Arctic sea ice is thinning much faster than they thought, and the meltdown is not slowing down.
Between 1975 and 2012, ice in the central Arctic thinned by 65 percent on average, and by 85 percent in September, when the ice cover is at a minimum, according to a new study published in The Cryosphere.
“The ice is thinning dramatically,” said lead author Ron Lindsay, a climatologist at the University of Washington’s 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.”
To track the decline of the ice in the pre-satellite era, the scientists used older data, including observations from submarines. The U.S. National Oceanic and Atmospheric Administration funded the effort to compile the various records and match them up for comparison.
“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 data also includes the NASA IceSat satellite that operated from 2003 to 2008, IceBridge aircraft-based measurements that NASA is conducting until its next satellite launches, long-term under-ice moored observations in the Beaufort Sea from the Woods Hole Oceanographic Institution, and other measures from aircraft and instruments anchored to the seafloor.
The older submarine records were unearthed for science by former UW professor Drew Rothrock, who used the U.S. Navy submarine measures of ice thickness to first establish the thinning of the ice pack through the 1990s. Vessels carried upward-looking sonar to measure the ice draft so they knew where they could safely surface. Further analysis of those records found a 36 percent reduction in the average thickness in the quarter century between 1975 and 2000.
“This confirms and extends that study,” Lindsay said. The broader dataset and longer time frame show that what had looked like a leveling off in the late 1990s was only temporary. Instead, adding another 12 years of data almost doubles the amount of ice loss, he explained.
Altogether, the data show the Arctic is changing faster than previously believed.
“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 new study, he said, also helps confirm the methods that use physical processes to calculate the volume of ice each month.
“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 new paper only looks at observations up to the year 2012, when the summer sea ice level reached a record low. The two years since then have had slightly more sea ice in the Arctic Ocean, but the authors say they are not surprised.
“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.”