Scientists have come up with a shockingly simple formula that lets individuals calculate exactly how much they are contributing to climate change.
For every tonne of carbon dioxide (CO2) a person produces, three square metres of Arctic sea ice melts, according to researchers at the Max Planck Institute for Meteorology in Hamburg, Germany, the National Snow and Ice Data Centre in Boulder, Colo., and the University College London in the U.K.
The findings, based on observational data from the 1960s to the present, were published in the journal Science.
"So far, climate change has often felt like a rather abstract notion. Our results allow us to overcome this perception," co-author Julienne Stroeve, an expert in sea ice satellite measurements at the National Snow and Ice Data Center, said in a release from the Max Planck Institute.
Taking a 4,000-kilometre road trip? That's three square metres of Arctic sea ice gone, by the team's calculations. A round-trip flight from London to San Francisco is five square metres.
Canadians emitted 20.6 tonnes of CO2 per person in 2014, according to Environment and Climate Change Canada.
If the average Canadian household has about three people, according to the formula, it it would take them about 8.5 years to destroy 1,579 square metres of Arctic sea ice — roughly the size of an NHL rink, not taking into account the thickness of the ice.
How much time do we have?
In a stable ice pack, the warming effect of infrared radiation generated by the sun is balanced by cold temperatures in the atmosphere. But increasing levels of carbon dioxide prevent those infrared rays from escaping into space.
As a result, the ice retreats northward where there's less solar radiation.
"The ice is migrating to re-establish equilibrium," said Stroeve.
Establishing that hard link between CO2 and sea ice has important consequences.
Rutgers University marine scientist Jennifer Francis, who wasn't part of the study, told The Associated Press the link is so clear and direct that "we know beyond a shadow of a doubt that Arctic sea ice is disappearing because of increased carbon dioxide."
For years, climate modellers have attempted to pinpoint when summer sea ice is likely to disappear. Some scientists have estimated the end of this century; others have said it should already be gone.
The study's authors say the most likely date is sometime around mid-century — unless CO2 emissions slow significantly.
That date is important for any number of reasons.
A seasonally open Arctic would ease northern shipping and resource development. It would be catastrophic for plants and animals that live on sea ice, as well as for the people who depend on them.
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It would also have unknown consequences for climate around the world. Sea ice is often referred to as the Earth's air-conditioning unit and it has been linked to the behaviour of the jet stream, a high-altitude river of air that influences rainfall, drought and extreme instances of both.
Sea ice affects more than just polar bears, said Stroeve.
"We are all ice-dependent species."
But not everyone's buying the study's simple formula.
"This sounds like a rather crude equation," Peter Wadhams, a professor of ocean physics at Cambridge University, told Reuters.
He said ice could disappear from the Arctic Ocean as early as 2017 or 2018 because of other factors triggered by human-made climate change, such as shifts in winds and rising sea temperatures.
In September 2016, sea ice shrank to an annual minimum extent of 4.14 million square kilometres, matching 2007 as the second smallest in the satellite record behind 2012.
Thursday's study said goals set under the 2015 Paris Agreement — which came into effect today — were insufficient to avert the loss of ice.
Governments meet in Marrakesh, Morocco, from Nov. 7-18 to work out how to implement the agreement.