Dirk Notz calculates that for every person who drives a car 1,000 miles or takes a round-trip flight from New York to London, three square meters (about 32 square feet) of sea ice vanishes from the Arctic. Researchers have long documented that human-fueled carbon dioxide emissions contribute to the overall warming of the planet — and, by extension, accelerate the diminishing of sea ice in the Arctic each year. But in a paper published Thursday in the journal Science, Notz and a colleague detail the complex set of calculations that allowed them to estimate how much Arctic sea ice melts...