Why is the Arctic melting faster than the Antarctic?

First, the bad news: The Arctic is melting much faster than expected, and could even be ice-free in summer by the late 2030s, a report from the Arctic Council's Arctic Monitoring and Assessment Program suggests. Previous studies had forecast an ice-free North Pole in summer by mid-century.

While the outlook is bleak for the Arctic, there is a silver lining for the Antarctic: The ice is melting at a slower rate than previously thought. Although glacier flow has increased since the 1990s, scientists from University of Leeds have found the melting rate to be only around a third of what was previously projected.

But the Antarctic is still melting. And a rapidly advancing crack in its fourth-largest ice shelf could soon see the largest icebergs ever recorded in human history break off into the sea.

Scientists agree that global warming causes both the ice in the North and the South Pole to melt. Air temperatures are climbing, and so are water temperatures. This makes the ice melt faster. The period of winter where the water is actually cold enough to freeze is getting shorter, which means ice floes are getting smaller.

The Arctic and Antarctic are far from "polar opposites" in the sense that ice at both is melting away in the face of climate change. But why are the Arctic and Antarctic melting at such a different pace?

Same same but different

Because the Arctic and Antarctic are cold, remote, and full of ice, they are often thought of as nearly the same. However, they are in fact quite different.

The first and most visible difference are the animals that call the frosty lands their home. Each polar extreme has a unique biome with many species that only survive there. Polar bears live in the Arctic and penguins only in the Antarctic, for example.

The second striking contrast is geography. The Arctic is a semi-enclosed ocean and almost completely surrounded by land. This means there is not much space for ice to float around. As a result, ice floes frequently bump into each other and pile up into thick ridges.

Arctic ice is thicker, and stays frozen longer during summer. In winter, the sea ice covers up to 15 million square kilometers (6 million square miles), and 7 million square kilometers remain at the end of the summer melt season.

The Antarctic is almost the geographic opposite of the Arctic - not just because it's on the other side of the world. The Antarctic consists of land surrounded by an ocean. The sea ice is free to move, and often floats northward into warmer waters where it eventually melts during the southern hemisphere's summer months.

In the Antarctic, almost all of the sea ice that forms during winter melts during summer. In the colder months, up to 18 million square kilometers (7 million square miles) of ocean is covered by sea ice, but by the end of the summer, only about 3 million square kilometers of sea ice remains.

Losses and gains

The growth and thaw of the ice is part of the annual cycle, and small fluctuations in the level of sea ice are normal. But scientists have observed a constant loss of sea ice in both the Arctic and Antarctic since the early 1970s.

According to the National Snow and Ice Data Center, a research institute affiliated with the University of Colorado, Arctic ice has been decreasing at an average rate of 3 percent per decade, while the Antarctic ice has increased slightly by about 0.8 percent per decade.

This is where it starts getting complicated.

While the overall trend in the Antarctic points to a regression of sea ice, it is also growing in some areas. As glaciers in West Antartica have melted, heavy snowfall in East Antarctica and the interior of West Antarctica led to an increase in ice sheets.

According to data from NASA, gains in ice have outweighed the overall losses from thinning glaciers from 1992 to 2008.

However, accumulation of snow in the Antarctic is actually a sign of global warming. The warmer the temperatures are, the more moisture is in the air. And the more moisture there is, the more snow falls.

Generally, the Antarctic tends to be more immune to global warming. Currents and winds tend to flow without interruption around the continent in a west-to-east direction, acting like a barricade to warmer air and water to the north.

The Arctic is missing such protective shields. Warmer waters from the south flow into the Arctic, preventing sea ice from forming.

Overall, the Antarctic is reacting far less to global warming than the Arctic. However, the level of sea ice is fluctuating strongly at both poles. In February, sea ice was at a record low both in the Arctic and Antarctic.