First it was the fault of Punxsutawney Phil, the groundhog who mistakenly forecasted a quick end to winter. Now climate scientists are saying that Arctic sea ice—or the lack of it—is a driving force behind the Northern Hemisphere's unseasonably cold spring.
As Northern Hemisphere temperatures remain below normal more than a week into the official start of spring, a team of meteorologists and climate scientists are pointing to recent research that suggests sea ice cover is a likely culprit.
Recent imaging from the U.S. National Snow and Ice Data Center showed a historic minimum in Arctic ice cover last fall, and current data reveals that sea ice cover—which recently reached its maximum for the year—is at its sixth lowest extent in the satellite record. (Related: "Arctic Sea Ice Hits Record Low—Extreme Weather to Come?")
Less Arctic sea ice—which is caused by global warming—alters atmospheric circulation in a way that leads to more snow and ice, said climate scientist Jiping Liu, who led a 2012 study on the topic published by the Proceedings of National Academy of Sciences.
It's a tough thing to understand. Less ice at the top of the world, often considered the planet's thermostat, might normally signal warmer global temperatures, not colder ones.
But the way weather works isn't so simple. Without a substantial ice cover, Arctic wind is less constrained. The jet stream—the belt of cool air that regulates weather around most of the Northern Hemisphere—then dips farther and farther south, bringing cold air from the Arctic closer to the Equator.
The result is much colder weather dipping into the spring much longer, and more forcefully, than normal. (See a world map of potential global warming impacts.)
Sea Ice Culprit
In trying to explain recent cold temperatures throughout the world, Liu and colleagues arrived at the melting Arctic ice by way of deduction.
"When we started to explore the reason why, our study suggested it was the decline of Arctic sea ice."
The problem is compounded by moisture. Arctic ice normally locks up water molecules that, in a liquid state, would evaporate and become rain. (Learn more about Earth's atmosphere.)
Less ice means more open ocean, allowing more moisture into the atmosphere to freeze and, eventually, fall. Arctic ice that melts, in effect, turns into snow in other parts of the world, like in Indiana or Missouri, which this week saw record levels of snow for this time of year.
Other researchers have had similar findings about how changes in some parts of the world will drive unexpected weather around the globe. (Read more about extreme weather in National Geographic magazine.)
A study released by the U.S. National Oceanic and Atmospheric Administration in 2012 signaled that low sea ice and increasing quantities of greenhouse gases in the atmosphere could lead to warmer summers as well.
"Simulations suggest that these summertime highs will intensify in the twenty-first century as a result of an increase in atmospheric greenhouse gas concentrations," the researchers soberly declared. (Learn about the greenhouse effect.)
Left unanswered are year-to-year anomalies, such as how last year's winter was unseasonably warm while Arctic ice continued to shrink.
Those freak seasons might continue to happen. But Liu and others believe that we're likely to see more longer and colder winters as the Arctic—and the planet in general—continues to warm.