The reduction in multiyear ice—commonly defined as ice that has survived for two summers—is so noticeable compared with previous editions that National Geographic Geographer Juan José Valdés calls it “the biggest visible change other than the breakup of the U.S.S.R.”
As the ocean heats up due to global warming, Arctic sea ice has been locked in a downward spiral. Since the late 1970s, the ice has retreated by 12 percent per decade, worsening after 2007, according to NASA. May 2014 represented the third lowest extent of sea ice during that month in the satellite record, according to the National Snow and Ice Data Center (NSIDC).
Ice loss is accelerated in the Arctic because of a phenomenon known as the feedback loop: Thin ice is less reflective than thick ice, allowing more sunlight to be absorbed by the ocean, which in turn weakens the ice and warms the ocean even more, NASA says.
Because thinner ice is flatter, it allows melt ponds to accumulate on the surface, reducing the reflectiveness of the ice and absorbing more heat. (See pictures of our melting world in National Geographic magazine.)
“You hear reports all the time in the media about this,” Valdés said. “Until you have a hard-copy map in your hand, the message doesn’t really hit home.”
Arctic Mapping
The multiyear ice—or older ice—is shown on the map as a large white mass; the maximum extent of sea ice—the pack ice that melts and refreezes with the seasons—is depicted as a line on the map, according to Rosemary Wardley, National Geographic’s senior GIS cartographer. In the 10th edition, which will be released September 30, the multiyear ice is much smaller in area than on previous maps. The 5th edition of the atlas, published in 1989, was the first to comprehensively map the Arctic.
Wardley and Valdés relied on two government resources that track Arctic ice data: NASA and the NSIDC. To map the multiyear ice, they took data from a 30-year study by NASA, published in 2012. “We wanted to have that comprehensive coverage,” Wardley said.
The total area of the existing ice at the end of the summer, which would include the remaining ice that was newly formed over the previous winter.
Scientists call that the total minimum sea ice cover, and it’s measured in September. (Total maximum sea ice cover is measured in March, at the end of winter.)
Without the minimum sea ice mapped, “ice that’s one year old or less is not being shown”.
Variable Ice
Meier is also concerned about relying on a single year-the new Arctic map draws from 2012 data, an extremely low year for ice cover.
Representing a dynamic environment in fixed form is always a challenge, said Valdés. Even so, atlases “open people’s eyes to what’s happening the world.”
— source news.nationalgeographic.com
People will never opens their eyes. This is part of class war