The vanishing veneer of frozen ocean isn’t just important for polar bears. The Arctic has seen better years than 2012. Its sea ice melted to an all-time low this summer, and by fall it was 18 percent smaller than at any point in recorded history. As U.S. scientists noted in their annual Arctic Report Card, the region’s sea ice is now “a younger, thinner version of its old self” — and that’s not as flattering as it sounds.
This year wasn’t just an anomaly, either. Arctic sea ice always waxes and wanes with the seasons, but its average late-summer minimum is now shrinking by about 13 percent every decade, according to the U.S. National Oceanic and Atmospheric Administration, and its six smallest Septembers have all occurred in the past six years.
Scientists widely agree the main catalyst is manmade climate change, boosted by a feedback loop called “Arctic amplification.” (Antarctic sea ice, meanwhile, is more buffered against warming and has actually expanded lately.) The problem has become well known even among laypeople, thanks largely to its compelling effect on polar bears.
But while many people realize humans are indirectly undermining sea ice via global warming, there’s often less clarity about the reverse of that equation. We know sea ice is important to polar bears, but why is either one important to us?
Such a question overlooks many other dangers posed by climate change, of course, from stronger storms and longer droughts to desertification and ocean acidification. But even in a vacuum, the decline of Arctic sea ice could be disastrous — and not just for polar bears. To shed some light on why, here are seven of its lesser-known benefits:
1. It reflects sunlight
Earth’s poles are cold mainly because they get less direct sunlight than lower latitudes do. But there’s also another reason: Sea ice is white, so it reflects most sunlight back to space. This reflectivity, known as “albedo,” helps keep the poles cold by limiting heat absorption. As shrinking sea ice exposes more seawater to sunlight, the ocean absorbs more heat, which in turn melts more ice and curbs albedo even further. This creates a “positive feedback loop,” one of several ways in which warming begets more warming.
2. It influences ocean currents
By regulating polar heat, sea ice also affects weather around the world. That’s because Earth’s oceans and air act as heat engines, moving heat to the cold poles in a constant quest for balance. One method is atmospheric circulation, or the large-scale movement of air. Another, slower method occurs underwater, where ocean currents move heat along a “global conveyor belt” in a process called thermohaline circulation. Fueled by regional differences in warmth and salinity, this drives weather patterns at sea and on land.