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sabato 5 novembre 2016

Destroying Arctic sea ice

The carbon dioxide emissions I produce as an average American destroy about 650 square feet of Arctic sea ice every year. That’s according to a new study that directly links the amount of annual CO2 released in the atmosphere to the amount of disappearing sea ice in the Arctic.


The findings, published today in the journal Science, could help scientists make better predictions about when exactly we’ll start seeing ice-free Arctic summers. The new calculations also show that previous climate models underestimated how much ice is lost — and that could have catastrophic consequences for our planet.
Every summer, the Arctic experiences some natural ice loss, but on average between 2.7 to 3.5 million square miles of ice persist. That ice is key because it acts like a refrigerator for the planet’s poles. If that ice disappears completely, the global temperature would rise and the planet would experience changing ocean currents and more severe stormsIt would also affect indigenous peoples who depend on sea ice for hunting, as well as species like polar bears and Arctic seals that depend on ice for their survival.
“It’s a scientific puzzle, what’s going on up there,” says Axel Schweiger, the head of the Polar Science Center at the University of Washington who was not involved in the study. “Increasing our ability to make predictions for the future will enable us to manage things better on the planet in terms of greenhouse gasses, hopefully, but also in terms of politics [and] mitigation strategies.” And today’s study is a new piece in this massive, complex puzzle.
Dirk Notz from the Max Planck Institute for Meteorology and Julienne Stroeve from the National Snow and Ice Data Center in Colorado analyzed the area of summer sea ice recorded between 1953 and 1978, and 1979 through 1997. They found that for every metric ton of CO2 emitted, about 32 square feet of summer sea ice disappeared. When they plugged their calculations into various climate models, they found a similar linear relationship — but the models significantly underestimated sea ice loss compared to what had actually been observed.
The reason for this relationship probably has to do with carbon dioxide’s notorious role as a greenhouse gas, Notz and Stroeve say. The amount of sea ice depends on a delicate balance with heat from the atmosphere and the Sun. If temperatures increase, the ice edge retreats north to a region with lower incoming sunlight to maintain that balance, and the ice cover shrinks. The authors estimate that by the end of the century, we will have ice-free summers in the Arctic, even if the global temperature increase is kept to just 2 degrees Celsius, like the Climate Paris Accord recommends.
“Their targets right now for what sort of warming to limit the planet to by the end of the century are not going to be enough, and ... they’re going to have to be more aggressive in reducing CO2 emissions,” Stroeve says. “We don’t really know the full implications of what could happen if we have no summer sea ice.”
The new projections are key for a number of reasons. Climate models are used as justification for protecting endangered species, for example. They’re also used to write up policies about climate change and global emissions. Finally, being able to tie a tangible change to individual carbon dioxide emissions could help drive home a sense of personal responsibility, Notz says. “There was always this feeling of ‘how much does it really help if I change my behavior?’” Notz says. “It really has changed the way I perceive my day to day actions.”

You can now calculate how much Arctic sea ice you’re destroying with your CO2 emissions Rachel Becker 

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