Thin Ice: The Arctic Meltdown Explained

Every year the sea ice in the Arctic reaches its maximum extent in the Northern hemispheric winter, usually in mid-to-late March. This image shows the maximum for 2007. CREDIT: NASA

If the North Pole becomes ice-free this summer — the odds for that are 50-50, one scientist says — that doesn't mean that the whole Arctic region will become an open ocean.

Mark Serreze of the U.S. National Snow and Ice Data Center in Colorado told The Independent, a London-based newspaper, "I'd say it's even-odds whether the North Pole melts out."

The article, posted on the newspaper's Web site Friday, generated some confusion as to what would actually happen at the North Pole, and in the Arctic Ocean as a whole, as the summer melt season gears up in the next few weeks.

In a telephone interview with LiveScience, Serreze explained that a melt-out at the North Pole wouldn't mean that all Arctic ice would melt. Rather, the thin, newly-formed ice around 90 degrees latitude could melt away for a few days. Such an event would be significant, he said, because any holes that have appeared in the ice at the North Pole up until now have been a result of winds pushing the sea ice around and creating cracks, not the melt-related processes that have taken hold in the Arctic in recent years.

Usually, the North Pole is covered with thick, perennial ice that forms over several years. But during last summer's record melt, which opened up the fabled Northwest Passage, a substantial amount of older ice melted. (Typically only the thinner, first-year ice melts in the summer, while the thick, perennial ice survives.) Average sea ice extent at the end of the summer was 1.65 million square miles (4.28 million square kilometers), almost 30 percent lower than the previous record low.

As winter cooled the Arctic waters, ice re-formed over the ocean, as it usually does. But this newly formed ice is thinner, first-year ice, more susceptible to melting once summer comes around again.

As it happened, wind patterns and ocean currents over the last few months moved that newly formed ice smack over the North Pole, setting up the situation where at least a temporarily ice-free North Pole could form.

"It's this symbolic thing, I think," Serreze told LiveScience. "This is where Santa Claus lives … it kind of hits you in the stomach."

The North Pole isn't the only part of the Arctic Ocean covered with this newly-formed ice — a substantial part of the region is capped by this thin frozen veneer. That "we're going to lose a bunch of ice," is more or less certain, Serraze said, but just where that melt will occur is "a roll of the dice."

One factor affecting where and how much ice will melt this summer is the somewhat higher ice extent that re-froze this winter. (While the winter extent was higher this year than last year, it was still about 390,000 square miles (1 million kilometers) smaller than average — that's equal to an area about the size of Texas and New Mexico combined.

Sea ice forms not by spreading out along the surface of the ocean, but rather as water just below the ice freezes onto the underside of the ice. This means that more ice probably also means slightly thicker ice, said Josefino Comiso of NASA's Goddard Space Flight Center, which helps monitor sea ice coverage. Thicker ice is more likely to survive the summer and become second-year ice, becoming thicker still in the winter.

The North Pole is also cooler than lower Arctic latitudes, meaning North Pole ice could better resist melting. Even if it does, there's still the possibility that winds could move the ice around so that a hole that formed at a lower latitude could be pushed over the North Pole, making it ice-free, Serreze said.

It's these weather patterns that scientists will be watching in the coming weeks to get a better sense of what will happen in the Arctic this summer. Serreze says that a warm spring season has put melting about on par with where it was at this point last year.

But other scientists say this summer's melt is unlikely to be as spectacular as last year's.

"We may not see a record minimum at all," said Tharston Markus, also of Goddard.

Scientists are monitoring the sea ice extent daily and say that after the main melt occurs over the next few weeks, they'll have a better idea of what the minimum extent, which typically occurs in mid-September, might be. For now though, all they can do is watch and wait.

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