The dramatic retreat of Arctic sea ice in recent years is changing disease patterns, altering the local food web and lowering the region's ability to reflect sunlight, according to two new studies.
The research in Science and Nature Climate Change, although on two different topics, fits into a growing body of knowledge about the side effects of ice loss. The papers also come as scientists say that Arctic ice extent could be near historic lows this year, even if it does not break last year's record.
This year "will without a doubt" rank in the top five lowest levels of ice extent ever recorded in the satellite era, and there is a good possibility that 2013 could rank second in terms of recorded ice lows, said Walt Meier, a scientist at the National Snow & Ice Data Center.
"It's kind of remarkable that it's as low as it is [this year], given that the weather conditions were not terribly optimal for ice loss," Meier said.
Distinctive weather patterns in 2013—such as extensive cloud cover in some areas—brought lower temperatures to the Beaufort and Chukchi sea regions, keeping ice loss off pace from last year, he said. Arctic ice will not reach its annual minimum until September, and "anything can happen" before then, but it would be unusual for there to be two record-breaking years in a row, he said.
Continuing a long-term retreat
What is important, Meier said, is that 2013 fits into the long-term trend of significant ice retreat and ice thinning from the 1970s and 1980s, despite year-to-year weather variations. The last six years have witnessed the six lowest minimum extents since satellite observations began in 1979, according to the National Oceanic and Atmospheric Administration.
"Even though some Arctic locations haven't been as warm this year, you can still melt through 3 feet of the ice, whereas in the past, you might have needed to melt through 6 or 8 feet of ice in that area," Meier said.
This ongoing ice retreat is spawning a variety of changes in the Arctic ecosystem, from increased parasites in caribou herds to a growth in annual tundra fires in Alaska, according to the assessment in Science last week, which reviews prior data.
Declining ice can change the timing of phytoplankton blooms, throwing off the feeding cycles of animals along the feed chain, it states.
Some changes are well-known, such as declines in polar bear populations and stresses to walruses being forced out of their shallow feeding grounds as ice retreats into deeper waters. Ice loss can cause less genetic diversity among animals like arctic foxes that use the ice as a travel pathway, while also creating the opposite effect with other species.
"Observed hybridization between polar bears and grizzly bears may be the result of increasing inland presence of polar bears as a result of prolonged ice-free seasons," the assessment notes.
Other changes are less visual. Diseases like phocine distemper virus, now present in eastern Arctic seals, may now "spill over" to western species because of the loss of ice, according to the review. On the other hand, some changing disease patterns could be beneficial— arctic foxes may not be able to carry rabies to Svalbard via an ice trek as they have in the past, for example.
Jedediah Brodie, a scientist at the University of British Columbia and study co-author, said a next step of research is determining which ecological changes in the Arctic are completely a result of ice loss, as opposed to climate change factors such as temperature increases.
"Most of the studies that we reviewed found plausible and even likely links between sea ice and things like polar bear breeding success, seal breeding success, plankton communities, and even climates in coastal terrestrial systems. But without actual experiments, we can't prove that sea ice is 100 percent the driver of those things," he said.
New 'benchmark' for loss of reflectivity
Another wild card is the loss of the albedo of the ice, or its surface reflectivity. As the ice thins and once-white areas turn to dark open waters, solar energy is absorbed rather than reflected back into space. This, in turn, can spur further ice melt.
The study released yesterday in Nature Climate Change breaks new ground by putting definitive numbers on the albedo effect, using satellite data. It confirmed that the mean albedo, or surface reflectivity, of the Arctic ice zone in late summer declined over an almost three-decade period, between 1982 and 2009. The average sea ice zone albedo for August was approximately 15 percent smaller in 2009 than it was in 1982, Aku Riihelä, a remote sensing scientist at Finnish Meteorological Institute and lead author of the study, said in an email.
The fact that reflectivity decreased in areas with dark water was not surprising, but there also was a decrease in reflectivity with remaining sea ice.
This "means that the average surface conditions are changing. There are more open water leads within the ice, and the surface melt of the sea ice is more intensive than before. The thinning and retreat of the sea ice thus seem to affect not only the marginal oceans of the Arctic, but also the inner parts," Riihelä added.
Mark Flanner, an assistant professor at the University of Michigan who did not participate in the research, said that several factors could reduce albedo of existing ice, including earlier snowmelt and melt ponds on top of the ice. Snow is very reflective, and its disappearance earlier in the year allows absorption of more solar energy. Those things, along with thinner ice that allows light to reach dark water, can help reduce albedo overall, he said.
The scientific community had an understanding that overall albedo decreases with declining ice, but the new study is distinctive for putting a number on the decline. That could help with projections of climate models and hypotheses of broader changes to the rest of the ecosystem.
"It will provide a benchmark," he said.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500
