The news from the poles has been grim lately.
In Antarctica, scientists are closely watching the Wilkins ice shelf after its last remaining ice bridge fractured. The massive ice shelf, the size of Connecticut, was already floating so it won’t raise sea levels as it breaks up in the ocean, but its demise is a harbinger of what could come for land-base ice sheets.
On the opposite end of the globe, satellite records released today reveal that 2008-09 was another bad winter for the thinning of the Arctic sea ice. The ice cap is thinning, and a decade-long trend of melting sea ice shows no sign of stopping.
Secretary of State Hilary Clinton cited those conditions as she called on participants at the Antarctic Treaty Consultative Meeting and Arctic Council today to increase protection of Earth’s polar regions. The Obama administration is urging strict limit on Antarctic tourism and increased environmental research in both regions.
“We are reminded that global warming has already had an enormous effect on our planet, and we have no time to lose,” Clinton said.
NASA officials described the Arctic region as “literally on thin ice” when they announced the latest sea ice satellite data. 2008-09 was the sixth worst winter since 1979, when the U.S. space agency began using satellites to measure the extent of sea ice in the Arctic – the top five were all in the previous five years. As Walt Meier, a cryosphere scientist at the National Snow and Ice Data Center, told reporters today:
"We’re in a very precarious situation."
Arctic sea ice traps the ocean’s heat, playing an important role in its circulation, while also cooling the air, effecting weather patterns, and reflecting solar radiation back into space. Reduced ice cover can push those natural systems out of balance. As Meier explains:
"That contrast between the cold pole and the warm equatorial regions and lower latitudes is one of the things that sets up your circulation patterns, your winds, your ocean circulation and essentially your weather patterns, and so all of those things are subject to change as the ice cover changes."
Satellite images from this winter reveal that the Arctic ice at its greatest was about 5.85 million square miles, roughly twice the size of the continental U.S. That was about 278,000 square miles – one Texas – less than the 1979-2000 average.
Each winter over the past decade, less ice has grown back, and that ice is thinner. In the past, thick ice that could survive the summers made up 30 to 40 percent of the Arctic’s sea ice. Now, it only makes up about 10 percent of Arctic ice, the data show. The other 90 percent is thinner, younger ice that is more prone to summer melting.
Scientists expect that trend to continue, both in sea ice and increasingly in land ice, said the National Snow and Ice Data Center’s Tom Wagner. The impact will be felt everywhere – in the Earth’s natural systems, in the lives of Arctic animals, and in changes for the rest of the planet’s inhabitants:
“The arctic sea ice is the defining characteristic of the Arctic ecosystems. All the animals that live in that part of the world depend on that ice, so if you take it away, you completely change all those animals – their home, the way they forage for food.
“It’s also important for us on the planet because it functions like a giant air conditioner. The Arctic sea ice, when it grows out, is essentially a giant mirror that is reflecting sunlight back into space. As that ice melts and goes away, it gets replaced by seawater, which is darker. You might think of it like a black tar driveway – when the sun hits that driveway, it heats it up. Well, when the sun hits that dark ocean, it also heats that up, and it helps heat the planet up over all, and it’s also a feedback to melt more ice.”
That feedback applies to land ice, as well. Scientists have also found a direct correlation between ocean temperature and the rate land ice in Greenland and Antarctica is melting and flowing into the ocean, Wagner said.
“The Earth’s polar regions are profoundly important to global climate – they’re one of the main parts of it. Everything is linked.”
Which takes us back to Antarctica.
The ice bridge connecting the Wilkins ice shelf to two islands began fracturing a few weeks ago, putting it on track to become the 10th known ice shelf of its size to break off in the past half century. A U.S. Geological Survey report released last week added the Wordie ice shelf and the northern part of the Larson ice shelf to the list of those that have completely vanished.
Glaciologist David Vaughan of the British Antarctic Survey predicted in 1993 that the Wilkins ice shelf was at risk from climate change – he notes that during the past 50 years, temperatures on the Antarctic peninsula have risen about 3 degrees Celsius – but he didn’t expect to see it break off so quickly.
"Climate warming in the Antarctic peninsula has pushed the limit of viability for ice shelves further south – setting some of them that used to be stable on a course of retreat and eventual loss. The Wilkins breakout won’t have any effect on sea-level because it is floating already, but it is another indication of the impact that climate change is having on the region."
Melting of the land-based ice sheets in Greenland and Antarctica would pose a greater threat, because they would raise sea levels.
"This continued and often significant glacier retreat is a wake-up call that change is happening in our Earth system and we need to be prepared," USGS glaciologist Jane Ferrigno said. "Antarctica is of special interest because it holds an estimated 91 percent of the Earth’s glacier volume, and change anywhere in the ice sheet poses significant hazards to society."
