The Arctic hasn’t been itself lately. Temperatures there are rising at twice the global rate, sparking an array of changes unlike anything in recorded history. One of the most striking examples is the region’s sea ice, whose dramatic decline over the past decade has led to forecasts of an ice-free Arctic Ocean as early as the 2030s.
Arctic sea ice always waxes and wanes with the seasons, but its average late-summer minimum is now shrinking by about 13 percent per decade, according to the U.S. National Oceanic and Atmospheric Administration. 2015 saw the fourth-lowest level on record, and the nine smallest Septembers have all been in the last nine years.
Scientists widely agree the main catalyst is man-made climate change, boosted by a feedback loop known as Arctic amplification. (Antarctic sea ice, meanwhile, is morebuffered against warming.) The basic 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 of climate change, from stronger storms and longer droughts to desertification and ocean acidification. But even in a vacuum, the decline of Arctic sea ice is disastrous — and not just for polar bears. To shed some light on why, here are seven of its lesser-known benefits:
- 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 their 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 warming begets more warming.
By regulating polar heat, sea ice also affects weather worldwide. That’s because the oceans and air act as heat engines, moving heat to the poles in a constant quest for balance. One way 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 local variations in warmth and salinity, this drives weather patterns at sea and on land.
The global conveyor belt of ocean currents, aka “thermohaline circulation.” (Illustration: NASA)
Declining sea ice has two main effects on this process. First, warming up the poles disrupts Earth’s overall heat flow by tweaking its temperature gradient. Second, altered wind patterns push more sea ice toward the Atlantic, where it melts into cold freshwater. (Seawater expels salt as it freezes.) Since less salinity means the water is less dense, melted sea ice floats rather than sinking like cold saltwater. And since thermohaline circulation needs cold, sinking water at high latitudes, this can halt the flow of warm, rising water from the tropics.
- It insulates the air
As cold as the Arctic Ocean is, it’s still warmer than the air in winter. Sea ice acts as insulation between the two, limiting how much warmth radiates up. Along with albedo, this is another way sea ice helps maintain the Arctic’s chilly climate. But as sea ice melts and cracks, it becomes dotted with gaps that let heat escape.
“Roughly half of the total exchange of heat between the Arctic Ocean and the atmosphere occurs through openings in the ice,” according to the National Snow & Ice Data Center.
“While the methane levels we detected weren’t particularly large, the potential source region, the Arctic Ocean, is vast, so our finding could represent a noticeable new global source of methane,” NASA’s Eric Kort said in a statement. “As Arctic sea ice cover continues to decline in a warming climate, this source of methane may well increase.”