27 August 2012 BBC
Arctic sea ice reaches record low, Nasa says
The melt season is expected to continue until the second half of September
The Arctic has lost more sea ice this year than at any time since satellite records began in 1979, Nasa says.
Scientists involved in the calculations say it is part of a fundamental change.
What is more, sea ice normally reaches its low point in September so it is thought likely that this year's melt will continue to grow.
Nasa says the extent of sea ice was 1.58m sq miles (410m sq km) compared with a previous low of 1.61m sq miles (4.17m sq km) on 18 September 2007.
The sea ice cap grows during the cold Arctic winters and shrinks when temperatures climb again, but over the last three decades, satellites have observed a 13% decline per decade in the summertime minimum.
The thickness of the sea ice is also declining, so overall the ice volume has fallen far - although estimates vary about the actual figure.
Joey Comiso, senior research scientist at Nasa's Goddard Space Flight Center, said this year's ice retreat was caused by previous warm years reducing the amount of perennial ice - which is more resistant to melting. It's created a self-reinforcing trend.
"Unlike 2007, temperatures were not unusually warm in the Arctic this summer. [But] we are losing the thick component of the ice cover," he said. "And if you lose [that], the ice in the summer becomes very vulnerable."
Walt Meier, from the National Snow and Ice Data Center that collaborates in the measurements, said: "In the context of what's happened in the last several years and throughout the satellite record, it's an indication that the Arctic sea ice cover is fundamentally changing."
“The summer ice volume is now only 30% of what it was in the 1980s”
-Prof Peter Wadhams Cambridge University
Professor Peter Wadhams, from Cambridge University, told BBC News: "A number of scientists who have actually been working with sea ice measurement had predicted some years ago that the retreat would accelerate and that the summer Arctic would become ice-free by 2015 or 2016.
"I was one of those scientists - and of course bore my share of ridicule for daring to make such an alarmist prediction."
But Prof Wadhams said the prediction was now coming true, and the ice had become so thin that it would inevitably disappear.
"Measurements from submarines have shown that it has lost at least 40% of its thickness since the 1980s, and if you consider the shrinkage as well it means that the summer ice volume is now only 30% of what it was in the 1980s," he added.
"This means an inevitable death for the ice cover, because the summer retreat is now accelerated by the fact that the huge areas of open water already generated allow storms to generate big waves which break up the remaining ice and accelerate its melt.
"Implications are serious: the increased open water lowers the average albedo [reflectivity] of the planet, accelerating global warming; and we are also finding the open water causing seabed permafrost to melt, releasing large amounts of methane, a powerful greenhouse gas, to the atmosphere."
1979 vs. 2007
The Mystery at the Heart of This Year's Record-Setting Arctic Ice Melt
By Alexis C. Madrigal theatlantic.com
You have probably heard that the Arctic has less sea ice right now than humans have ever recorded. The new record, set yesterday, beat the previous low, which was measured in September 2007.
"By itself it's just a number, and occasionally records are going to get set," said National Snow and Ice Data Center scientist Walt Meier in an official statement. "But in the context of what's happened in the last several years and throughout the satellite record, it's an indication that the Arctic sea ice cover is fundamentally changing."
There are two odd things about this sad record of global change.
First, it's only late August, several weeks before the traditional time when the sea ice melting stops. So we may have several weeks to go of melting, in which case, this year's low could not just break but shatter 2007's record.
Second, if the melt continues for days or weeks more, the melt will end up catastrophically lower than anyone anticipated.
After 2007's low -- which scared many Arctic scientists into statements like, "The Arctic is screaming" -- the sea ice up north recovered, though not to pre-2007 levels. Counting this year, the six years with the least sea ice on record all occurred in the last six years.
In that sense, it is not a monumental surprise that 2012 did not see an overabundance of sea ice or return to the norms of earlier this century. On the other hand, the catastrophic drop off of sea ice in the last few weeks was not something that was easy to model or predict.
Each year, a program called the Sea Ice Outlook gathers predictions about sea ice from different teams of scientists. The groups use different techniques to predict what the next summer's ice melt season might look like. Some do straight statistics, others build models, and other groups use heuristics or a combination of methods. Teams can submit in June, July, and August. In all cases, they are all trying to guess how much sea ice will be left in the Arctic come mid-September, which (as noted above) had traditionally been the low point. The measure that scientists use to describe the sea ice's extent is the millions of square kilometers of ice that our satellites can see from orbit.
In May of this year, it looked as if the Arctic was going to have a year much like the past four, if a little worse. A lot of ice would melt, more than in any of the years before or since 2007's record-setting low, but none predicted a catastrophic year. The median guess was 4.4 million square kilometers of sea ice would be left, and the band was pretty tight around that number, with only a single group predicting a sea ice extent of 4.1 million square kilometers or lower. A few numbers for comparison: The average low from 1979 to 2000 was 6.7 million square kilometers. In 2010 and 2011, 4.9 and 4.6 million square kilometers of sea ice remained in September. The record low was 4.17 million square kilometers of sea ice in 2007.
And it is this last number that the Arctic crashed through this week with a measurement of 4.1 million square kilometers of sea ice left.
Now, the modelers may not turn out to have been wrong if, as we mentioned above, the sea ice melt season ends early. "We'll see how September turns out," Robert Grumbine, an ice modeler with the National Oceanic and Atmospheric Administration who worked on three of the predictions, told me. "It isn't unheard of for the annual minimum to be about now, rather than in September."
Some of the more recent (July and August) predictions for the Sea Ice Outlook have revised their estimates downwards on the basis of the early summer. Nonetheless, it still stands: going into this summer, we were not expecting a record low for sea ice.
And now here's the most recent data.
What's befuddling about 2012, relative to 2007, is that the Arctic has not seen the kind of ice-melting weather that 2007 did. "I'm at a loss at this loss," wrote sea ice blogger (yes they exist!) Neven Acropolis. "The 2007 record that stunned everyone, gets shattered without 2007 weather conditions."
Unknown unknowns aside, one frightening possibility exists. For years, scientists have been warning that Arctic sea ice is thinning. Thinner ice melts more quickly. But when we traditionally measure sea ice, scientists aren't looking at the mass of the ice, just the surface extent.
Unfortunately, as the University of Washington's Polar Science Center explains, we can't monitor sea ice volume easily.
"Sea ice volume is an important climate indicator. It depends on both ice thickness and extent and therefore more directly tied to climate forcing than extent alone. However, Arctic sea ice volume cannot currently be observed continuously. Observations from satellites, Navy submarines, moorings, and field measurements are all limited in space and time. "
So, scientists have to take these limited readings and build a model that estimates the sea ice volume. They call it PIOMAS, a catchy acronym for the Pan-Arctic Ice Ocean Modeling and Assimilation System. Obviously, as with any model, there are limitations to its predictive power. But in recent years, and even more dramatically in recent weeks, PIOMAS has been showing a major anomaly relative to the longtime average in ice thickness. Even where there has been ice in the Arctic, it's much thinner than it used to be.
If this year's melt continues and the amount of sea ice in the Arctic reaches even lower, it may be confirmation that the ice really is that thin and easier to melt, perhaps introducing other dynamics that seem poised to accelerate the decline of the system. The climate change signal, in other words, is growing stronger as the Arctic moves toward ice-free summers. Jennifer Francis of Rutgers, as quoted on Dot Earth:
"The fact that the ice is so dramatically thinner now than it was only 20 years ago means that it is vulnerable to any abnormal weather event or fluctuation in ocean currents. If the "perfect storm" of atmospheric and oceanic conditions that led to the 2007 record, or the patterns that reduced ice this summer, happened back in the thick-ice era, sea-ice loss would not be making headlines. Following this summer's new record ice loss, the Arctic will enter a winter with even less ice than ever before, leading to even thinner ice, which barring any monumental external events like a major volcanic eruption, will likely perpetuate the trend in sea ice decline."
Arctic ice melt 'like adding 20 years of CO2 emissions'
The loss of Arctic ice is massively compounding the effects of greenhouse gas emissions, ice scientist Professor Peter Wadhams has told BBC Newsnight.
White ice reflects more sunlight than open water, acting like a parasol.
Melting of white Arctic ice, currently at its lowest level in recent history, is causing more absorption.
The Cambridge University expert says that the Arctic ice cap is "heading for oblivion".
In 1980, the Arctic ice in summer made up some 2% of the Earth's surface. But since then the ice has roughly halved in area.
"Thirty years ago there was typically about eight million square kilometres of ice left in the Arctic in the summer, and by 2007 that had halved, it had gone down to about four million, and this year it has gone down below that," Prof Wadhams said.
And the volume of ice has dropped, with the ice getting thinner:
"The volume of ice in the summer is only a quarter of what it was 30 years ago and that's really the prelude to this final collapse," Prof Wadhams said.
Parts of the Arctic Ocean are now as warm in summer as the North Sea is in winter, Prof Wadhams said.
The polar ice cap acts as a giant parasol, reflecting sunlight back into the atmosphere in what is known as the albedo effect.
But white ice and snow reflect far more of the sun's energy than the open water that is replacing it as the ice melts.
Instead of being reflected away from the Earth, this energy is absorbed, and contributes to warming:
"Over that 1% of the Earth's surface you are replacing a bright surface which reflects nearly all of the radiation falling on it with a dark surface which absorbs nearly all.
"The difference, the extra radiation that's absorbed is, from our calculations, the equivalent of about 20 years of additional CO2 being added by man," Prof Wadhams said.
If his calculations are correct then that means that over recent decades the melting of the Arctic ice cap has put as much heat into the system as all the CO2 we have generated in that time.
And if the ice continues to decline at the current rate it could play an even bigger role than greenhouse gases.