Mexico-Size Chunk of Ice Missing from the Arctic

The Arctic is missing a chunk of sea ice the size of Mexico.

While fall ushers in the season of sea ice growth, November saw a brief retreat that was virtually unprecedented in nearly 40 years of satellite records, according to data released Tuesday by the National Snow and Ice Data Center. That dip helped November set a record low for sea ice area — the seventh month to do so this year, also a record.

At the opposite pole, the sea ice fringing Antarctica also set a record low for November, reversing several years of record highs, though what's driving the flip-flopping isn't clear.

"It is very striking this November in both hemispheres," NSIDC scientist Julienne Stroeve said in an email. "It certainly is continuing the long-term decline in Arctic sea ice. It's a bit more curious about what is happening in Antarctica, so more research on that is needed."

Unusual Cold Season Retreat

Arctic sea ice follows a seasonal cycle, waxing during the cold, dark months of fall and winter, and waning when the sun re-emerges in spring and summer.

But skyrocketing Arctic temperatures, which are rising twice as fast as the global average, have set off a downward spiral in sea ice levels. Summer has seen the biggest decline, with the end-of-season minimum half of what it was just three decades ago.

A recent study found that emissions of carbon dioxide equivalent to that from a single transatlantic flight translates to a loss of 30 square feet of sea ice. If emissions aren't brought under control and temperatures continue to rise, the Arctic could become ice-free during summer by the middle of the century.

That loss of ice affects regional flora and fauna, native communities, and industrial activities like shipping. It may even exert an influence on weather patterns of North America, Europe and Asia.

The end-of-winter maximum this year hit a record low thanks to remarkably warm winter conditions in the Arctic, with air temperatures 4°F to 11°F (2°C to 6°C) above average. But relatively cool and cloudy summer weather kept the summer minimum from beating out the 2012 record low.

As the sun set for the winter, ice began to grow like usual, though it stayed well below normal week after week.

Then, in mid-November, an odd thing happened: the sea ice began to decline. Before it resumed its upward trajectory, sea ice area dropped by 19,300 square miles — a feat virtually unprecedented in the records. The only similar occurrence was a much smaller drop of 5,400 square miles in November 2013.

That unusual cold-season dip helped November finish with a sea ice area 753,000 square miles below the 1981 to 2010 long-term average for the month (even though the growth rate of sea ice was slightly higher than average), just a bit smaller than the area of Mexico.

Not a ‘Tipping Point'

The strange cold-season dip in sea ice extent was caused by persistent southerly winds pulling in warm air and warm ocean waters that kept sea ice from forming in the Barents Sea, an area north of Scandinavia and eastern Russia. Sea surface temperatures there were up to 7°F (4°C) above normal during November near Norway's Svalbard Peninsula.

"Typically sea ice begins to form in the fjords at the beginning of November, but this year there was no ice to be found," Stroeve, who was in Svalbard during the month, said in a statement.

Sea ice also dropped unusually sharply in Antarctica, which is nearing summer. The average November extent there was 699,000 square miles below the 1981 to 2010 average, more than twice previous record low for month. NSIDC scientists think the decline was due to warmer air temperatures and a rapid change in the air current that whips around the continent.

In previous years, Antarctic sea ice hit record highs, potentially due to changing ocean conditions linked to the melting of land-bound glaciers. But polar scientists say there is still much to learn about what drives the behavior of Antarctic sea ice, which is quite different than its Arctic cousin.

Stroeve and other sea ice researchers don't think this year's Arctic ice records mark a tipping point, or a point where such loss becomes irreversible. Scientists worried about reaching such a point-of-no-return when sea ice first plummeted to a record low in 2007, but it has since rebounded (though the long-term decline continues) and if warming is brought under control, sea ice can grow back.

"I still don't think we have a tipping point only because the ice could come back if we limit the warming — it's not irreversible," Stroeve said.

It is possible, though, that such a cold season retreat could become more common as global, and Arctic, temperatures, continue to rise.

"I think this is something we might expect to see more of in the future," Walt Meier, a NASA sea ice researcher, said. "With less ice in the summer and more warming of the ocean, there is more heat available near the ice that can be pushed (by winds) into the ice [and] at least temporarily melt back some ice early in the growth season."

Unfrozen: Greenland Was Once Ice-Free for 280,000 Years

More than a million years ago, frosty Greenland was ice-free, its bare bedrock exposed for 280,000 years, researchers have found.

During this exposed stint, the island's overall ice cover could have dropped by more than 90 percent, the scientists reported today (Dec. 7) in the journal Nature.

Previous studies have reported that Greenland's ice shrank in the distant past, but this study is the first to explain how long a span Greenland may have endured without its usual frozen cover. This discovery hints that its surface ice was more variable than once thought — which does not bode well for its future stability in a warming world, the researchers said.

As valuable as moon rocks

The study authors gathered their data from isotopes — atoms of the same element but with a different number of neutrons — extracted from bedrock minerals. The isotopes, beryllium 10 and aluminum 26, are produced only by cosmic rays, which means that they only occur when the rock that holds them is exposed; as such they can offer clues about when rocks were bare of ice, and for how long.

These isotopes originated in the only rocky core ever extracted from land underneath Greenland ice, drilled at the Greenland Ice Sheet (GIS) summit in 1993.

Minerals from this solitary core are second only to moon rocks in their rarity and importance, as they are the only existing evidence of Greenland's ice-covered extant bedrock, according to lead author Joerg Schaeffer, a paleoclimatologist with the Lamont-Doherty Earth Observatory, and a professor with the Department of Earth and Environmental Sciences at Columbia University.

When this core was first examined decades ago, researchers were able to detect isotopes in the sediment produced by cosmic rays, but their equipment wasn't sensitive enough to gather precise climate data, Schaeffer told Live Science. In order to get to the isotopes, "we literally digested those rocks," he said, describing how he and his colleagues dissolved minerals with acid so they could observe the atoms.

The atomic isotope beryllium 10 told the scientists that the rock had at one point been ice-free. To gauge how long that period lasted, they compared the amount of beryllium to quantities of aluminium 26. It appears at a 7 to 1 ratio to beryllium 10, but decays twice as fast. The quantity of aluminium atoms relative to beryllium told the scientists that once the ice cover melted away, the rock was exposed for more than 280,000 years, until about 1.1 million years ago.

The extent to which Greenland's ice may have waxed and waned over time was the subject of another new study, also published today (Dec. 7) in Nature. Lead author Paul Bierman, a professor of geology at the University of Vermont, told Live Science that the study found evidence of ice covering the island for a period of 7.5 million years, a much longer period than described in any prior study.

A patchwork history

Though many scientists have investigated Greenland's ice for clues about its behavior over time, a comprehensive picture long remained elusive. And Greenland itself is to blame for this incomplete view, as recurring changes in ice cover scrub away geologic evidence over and over again, Bierman said. ['Dark Ice' Speeds Up Melting in Greenland (Photos)]

"Whenever the ice expands, it wipes away what it did last time," Bierman told Live Science. "It's like looking at a chalkboard that's been erased, and you have to figure out what happened three classes ago."

Bierman and his colleagues analyzed deep-sea samples from a core of weathered bedrock that originated in East Greenland, but was carried into the ocean off the coast.

Their examination revealed that during the past 7.5 million years, Greenland ice was "persistent" but also "dynamic," the scientists wrote in the study, allowing that there were likely periods when the ice cover dwindled due to global temperature changes.

Addressing uncertainties

While Bierman's study suggests that ice consistently blanketed Greenland, that doesn't necessarily rule out that some parts of the island were ice-free at times. High-altitude regions in the east could have stayed frozen even during warm conditions, while other parts of Greenland lost their ice, according to Ginny Catania, an associate professor with the Jackson School of Geosciences at the University of Texas at Austin.

Catania, who was not involved in the new studies, told Live Science in an email that both investigations support reduced ice in Greenland's past, but more data would be required to understand the processes that contributed to massive and rapid ice loss, and how they might drive future melt.

"These uncertainties limit our ability to accurately predict the future of the ice sheet," Catania said. "We are in for a lot of change in Greenland in the future. The question remains — how quickly will it happen?"

Techniques used in both studies introduce novel methods for looking at how Greenland's ice changed, but there is still more work to be done. Determining more precisely when and why historical ice loss happened could greatly improve computer models that would find a threshold for instability in Greenland's ice today, according to Anders Carlson, an associate professor of geology and geophysics with the College of Earth, Ocean and Atmospheric Sciences at Oregon State University.

"Regardless of when Greenland had ice-free conditions, the ice sheet has been unstable and collapsed in the past," Carlson told Live Science. "And that probably occurred when CO2 [carbon dioxide] levels were below what they are now — which bodes ill for future," he said.

And time may be running short. Seasonal melt for Greenland in 2016 was above average, with the third highest surface mass loss of ice in 38 years of satellite observations, according to the National Snow and Ice Data Center. Were Greenland to lose the majority of its ice, as it did in the past, the water released into the world's oceans could produce around 23 feet (7 meters) of sea level rise, Schaeffer added.

"We have never seen the planet warming as fast as it is now, and we have to prepare as best we can," Schaeffer told Live Science. "We need to get organized quickly, and, hopefully, this helps to make the case."