Polar bears are the poster children for the rapid loss of sea ice in the Arctic. ©Henry H. Holdsworth

Cute, adorable animals are often used to garner support for environmental causes in places that are remote. After all, it’s hard to have concern for an area that is at the opposite end of the Earth from where you live and for which you have no plans to ever see. It’s why polar bears, for example, have been used as the poster children for the rapid loss of sea ice in the Arctic ever since “global warming” became a household phrase decades ago.

Today, scientists largely agree that humans have been major players in that loss. Recently, in fact, researchers have found that neither natural climate fluctuations nor self-acceleration can explain the observed Arctic sea-ice retreat. Instead, they’ve found a strong, plausible correlation with increasing greenhouse gas concentrations—increasing as a result of human activities.

What is surprising, though, is that at the opposite end of the Earth, no such link between greenhouse gas concentrations and retreating sea ice has been found. In truth, Antarctic sea ice is actually gaining ground.

So, if we’re losing ice at one end of the planet, but gaining at the other, is there cause for concern?

Unlike the Arctic, Antarctica is an icy continent surrounded by water. ©Colin McNulty

In the Arctic

When trying to assess the cause of weather patterns, scientists usually employ complex climate models. But recently, at Germany’s Max Planck Institute for Meteorology, researchers attempting to identify what could be causing the observed sea-ice loss in the Arctic tried a different strategy. Instead of using standard climate models, they used historical records that described the natural variations of sea-ice extent between the early 1950s and late 1970s. These natural fluctuations were then compared to the magnitude of fluctuations of the Arctic sea-ice cover—as measured from satellites—since the late 1970s.

From such a comparison, the scientists found only a minute possibility that the recently observed lack of sea ice in the Arctic simply happened by chance. They also found that whenever there was a strong sea-ice loss from one year to the next, the extent of the ice always recovered somewhat in the following year. This would not be the case if the sea-ice retreat were self-accelerating.

Having excluded natural fluctuations and self-acceleration as the main drivers for the sea-ice retreat, the scientists then examined other possible factors, such as solar radiation, prevailing wind patterns, volcanic eruptions, oceanic heat transport and cosmic rays. No plausible link to any of them could be established.

In the Antarctic

In the Antarctic, however, the situation is different. Here, the sea-ice cover is slightly increasing—all the while the sea-surface temperature around Antarctica has risen.

Obviously, greenhouse gases are not having the same effect in the South as they are in the North. So veteran climate researchers—looking beyond the usual climate models again—analyzed Southern Ocean temperature records and simulations of sea-surface temperatures. They found that higher sea-surface temperatures during the last half of the 20th century probably sparked the hydrological cycle above the Southern Ocean, creating a scenario in which more sea ice can grow. Higher sea-surface temperatures increase evaporation in more temperate zones, which increases snowfall closer to Antarctica. And that extra precipitation adds another factor that helps to grow sea ice: it lowers the salinity of the surface water, slowing the melting of sea ice.

If the same thing happens in Antarctica that is occurring in the Arctic, we soon all may be in over our heads. ©Colin McNulty

It now appears that the major reason for the discrepancy in sea-ice loss and gain at the two poles lies in the different landmass distributions in the two places. In the Arctic Ocean, the ice is virtually landlocked, and its melting and freezing determines its extent. Therefore, greenhouse gases play an important role in the North.

But in Antarctica, the sea ice is free to drift around in the open Southern Ocean. The prevailing winds and ocean currents govern the extent of the ice there. So, in one case, there is an icy ocean surrounded by land. In the other, there is an icy continent surrounded by icy water. It makes all the difference.

It could soon be the same animal

The Antarctic sea ice’s apparent immunity to global warming, however, could be temporary. If the sea and air warm even more in the 21st century as projected, much of the extra snowfall in the Antarctic could turn into rainfall, which would rapidly melt ice all around the southernmost continent.

For most of us, traveling to the Arctic or Antarctica would be just about the most far-flung adventures we could have—and therefore out of reach. So should the probability of future sea-ice loss in Antarctica concern us, especially in light of all the other environmental causes that need our attention? It’s hard to drum up concern for a place actually gaining ice.

The Sierra Club reports that satellite measurements taken from 2003 to 2010 indicate that the Earth lost 1,000 cubic miles of ice—enough to cover the United States in a foot and a half of water. And in the U.S., the winter of 2011-2012 proved to be the fourth warmest in recorded history—a phenomenon that could be linked to the loss of summer sea ice in the Arctic.

If the same thing happens in Antarctica that is occurring in the Arctic, we all may be in over our heads soon.

Here’s to your adventures, in whatever corner (or end!) of the world you find them,

Candy