Calculating your role in melting Arctic sea ice: How the CO2 emissions add up.

Climate scientists have calculated just how fast humans' carbon emissions are melting Arctic sea ice in a new study. Just 75 miles in a fossil-fuel powered car equals one square foot of ice melted Arctic ice.

Sorry polar bears, the Arctic Ocean might be free of sea ice before 2050. 

According to new calculations, for every metric ton of carbon dioxide emitted, about three square meters (approximately 32.3 square feet) of Arctic summer sea ice disappears. And, with humans currently emitting about 35 billion to 40 billion tons of CO2 each year, the future doesn't look very frozen. [Editor's note: An earlier version understated human CO2 emissions.]

It's not hard to rack up those emissions. About 2,433 miles of driving – roughly the distance from Washington, DC to Las Vegas – or just one seat on a return flight from New York to London – on average produces a metric ton of CO2 emissions. Or, for those who aren't long-distance travelers, just over 75 miles of driving in a typical fossil-fuel powered car produces enough emissions to melt one square foot of ice.

That's according to Dirk Notz, head of a research group at the Max Planck Institute for Meteorology in Germany that studies sea ice. Dr. Notz calculated the relationship between CO2 emissions and the loss of Arctic summer sea ice as lead author of a paper published Thursday in the journal Science.

"Our study now provides individuals with the sense that their own individual actions make a difference," Notz tells The Christian Science Monitor in a phone interview. "If I decide to drive my car a little less or to buy a car that uses less fuel, for example, all these little actions will make a difference for sea ice."

Technically, Notz has calculated when there will be less than 1 million square kilometers (386,000 square miles) of Arctic sea ice left in September, after summer melting, a measurement commonly used to define sea ice free conditions. Winter temperatures will continue to freeze parts of the Arctic Ocean.

That 1 million square kilometers "seems like quite a lot of ice," says Walter Meier, a sea ice researcher at the NASA Goddard Space Flight Center who was not part of the study. "But in reality it's not that much."

"The Arctic Ocean will be for all intents and purposes a blue Arctic Ocean" when that happens, he says.

Dr. Meier says Notz's calculations oversimplify the relationship between carbon emissions and Arctic sea ice loss. "The climate system is, in reality, a lot more complex than that," he says in a phone interview with the Monitor. 

Kevin Trenberth of the the Climate Analysis Section at the National Center for Atmospheric Research, who also was not part of the research, agrees. "I think it's too simple because it doesn't deal with ocean transports and it doesn't deal with atmospheric transports," he says in a phone interview with the Monitor. Furthermore, Dr. Trenberth says, seasonal variations complicate trends so the calculated relationship between CO2 and sea ice loss could be off.

Although he questions their methods, Trenberth agrees with the researchers that the Arctic will see an ice-free September. And, he says, it could be as soon as in the 2030s.

What would a world with a blue Arctic look like?

"We're changing ice that has been around for many years to, mostly, ice that forms every year," James Overland, an oceanographer at the NOAA Pacific Marine Environmental Laboratory who was not part of the study, tells the Monitor in a phone interview. In decades past, ice would build up and become thicker through the winter. While some of that ice would melt during the summer, most would remain to accumulate more ice year after year.

Animals like polar bears and walruses use those thicker sheets of ice as a sort of home base when hunting. Thinner and more fragmented ice could destroy their lifestyles. And that's not just true for animals; a disrupted icy ecosystem could make it more difficult for native human populations to hunt and forage too. 

But loss of Arctic sea ice probably won't just have a local impact. 

"Arctic sea ice regulates the temperature of our planet by cooling the Atlantic and Pacific waters," David Barber, a sea ice and climate scientist at the University of Manitoba, who was not involved in the research, writes in an email to the Monitor.

Some research has suggested that less Arctic ice could lead to a weakening of the jet stream, an atmospheric system that affects the global climate. This shift could be leading to more extreme weather events, like flooding, freezing, and even droughts, already.

And on top of that, Arctic sea ice serves as a sort of refrigerator for the planet, Notz explains. When the summer sun rays hit the vast, bright ice, much of that energy is reflected back. But the dark waters of a blue ocean will absorb that heat, leading to even more warming and melting.

Then, warmer, more wave-filled waters can eat away at other geological features, including glaciers, coastlines, and permafrost, in a spiral of changes. 

It is important to note, however, that melting Arctic sea ice will not directly raise sea levels. Like melting ice in a soda glass, the oceans won't spill over from ice that is already floating in water. But as ice on land, such as the Greenland ice sheet, melts as an indirect effect of the disappearing sea ice, that water will flow into the oceans and raise sea levels. 

Saving the ice

The Paris climate agreement is set to go into effect Friday with the aim of meeting an ambitious goal: preventing global temperatures from rising 2 degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels.

But, by Notz's calculations, Arctic summer sea ice will already be gone if temperatures reach that threshold. That sea ice could survive, however, if the more aggressive target of 1.5 degrees Celsius warming is attained.

Further complicating things, the Arctic is heating up faster than the rest of the world, perhaps two or three times faster, Notz says. 

Trenberth points out that greenhouse gas emissions can also have a delayed effect. So even if humans suddenly stopped emitting carbon altogether, temperatures likely still would rise. And, he says, although scientists have been discussing ways to extract CO2 from the atmosphere, "this is an extremely difficult thing to really achieve."

Looking at the sea ice loss in the Arctic is "a really stark indicator of climate change," Meier says. 

"We think of the Arctic as a cold place, but in a lot of ways it's relatively warm," he says. During the summer, many sections sit on the cusp of the freezing point. So, while the difference between 80 and 82 degrees Fahrenheit might not make a huge difference in Washington D.C., Meier explains, if you go from 31 to 33 degrees in the Arctic, it's the difference between ice skating and swimming.

While this study doesn't really add new information for scientists, Meier says, with Arctic sea ice far from most people's everyday lives and carbon emissions, "it really helps people understand and visualize the impact."