The melting of Arctic sea ice may seem like an intangible, far-off problem, but what if there was a way to know how much you are personally contributing to the melt? A new study, released today in the journal Science, allows you to do precisely that.
The study makes a direct link between the amount of anthropogenic carbon dioxide emissions and sea ice loss, finding that for each metric ton of CO2 emitted during the period between 1953 and 2012, roughly 32 square feet of sea ice was lost.
The study's authors, climate scientists Dirk Notz and Julienne Stroeve, applied this finding to per capita emissions data from 2013 for each country, and found that the average person causes the loss of hundreds of feet of sea ice each year. But the U.S. and other high-emitting countries like Australia, Saudi Arabia and the United Arab Emirates are not average. Americans, for instance, have a personal footprint of as much as 645 square feet of ice loss. China, a large emitter but with a massive population, has lower per-capita emissions, with up to 322 square feet of ice loss per person.
Ice-free summers are edging ever closer in the Arctic. According to the National Snow and Ice Data Center, Arctic sea ice has declined an average of 13.3 percent each decade since 1979. This year's low point was the fifth-lowest on record, and after an initial period of rapid freeze, levels are now at record lows. In addition to providing a habitat for polar bears and an entire ecosystem, sea ice also acts as a refrigerator for the globe. It keeps the Arctic cool and moderates temperatures worldwide.
The study found that with an additional 1,000 gigatons of CO2 emissions, summer sea ice would be gone. That's also the amount of emissions associated with 2 degrees Celsius of global warming. So even if we are able to meet the global goal of keeping warming to 2 degrees Celsius above preindustrial temperatures, it won't be enough for the sea ice.
"For most climate change parameters, the change between 1.5 degrees and 2 degrees might be quite gradual," said Notz, who heads the sea ice research at the Max-Planck-Institute for Meteorology in Hamburg, Germany. "But for Arctic sea ice, the difference means whether there is still Arctic summer sea ice in the future or whether there isn't."
The study found that the globe will hit that point sometime in the middle of the century, though Notz said not to focus on the actual date at this point. "There's not a God-given year as to when Arctic sea ice will be gone," he said. "Whether we spend those 1,000 gigatons over 30 years or spend it all next year or over 200 years doesn't really matter to the ice."
Cecilia Bitz, a sea ice and climate scientist at the University of Washington, who was not affiliated with the study, said she found the approach novel because it allows people to understand their impact on sea ice. "Having stood on sea ice myself, I can really picture now how much I'm responsible for," she said. "The size of my front yard—each year."
In the study, the authors wrote that more ice has been lost than expected based on previous models.
Bitz, however, argued that observed ice loss does fall within the models' predicted range—albeit at the edge of the range. That means a low probability event is happening, indicating that the models might not be sensitive enough.
She also cautioned that there should be a greater degree of uncertainty in the Notz and Stroeve findings. Typically, sea ice models are based on the historical records dating back to 1979, the beginning of the satellite era. Notz and Stroeve's work relies on shipping records for the period from 1953 to 1979, which have a higher degree of uncertainty.
Even so, Bitz said the basic findings were sound. And the idea of individual contributions to sea ice loss is an impactful one and it might help drive home the idea that everyone's actions have a direct impact on climate.
Notz said that was what he found the most significant, too.
"Whenever I go to the Arctic, and I bring home photos and show them to my kids, it feels awkward to know that because of our actions when they are at our age all that beautiful landscape could be gone," he said. "That does something to us humans. To know that the North Pole could no longer be out there as a place, just a spot in the ocean."