Sea ice can be very thick…even in a warming world (Pic: I.Quaile)

The recent publication of a study on Arctic ice as measured by the “yellow submarine”, an underwater robot, caused a flurry of comments on the “climate hoax” by some of those of a “climate-sceptical” persuasion. I contacted a sea ice physicist at Germany’s AWI Institute for an independent opinion. Here’s the background:

Measurements conducted by an underwater robot have found that Antarctic sea ice is much thicker than previously thought in some places. Much of this floating sea ice is underwater, hidden from the satellites which have been tracking seasonal sea ice for decades. The satellite data is normally validated by drilling into ice floes which can be reached by ship, or visual estimates from the ships themselves. However, it is difficult to reach the thickest ice that way.

Underwater robot below the ice

Over the last four years, an international group of researchers has been mapping the bottom of sea ice in several areas of the Antarctic using an underwater robot, or AUV. It can swim to a depth of some 30 metres (100 feet) and uses sonar directed upwards to survey the bottom of the sea ice. This gave them access to areas where measurements could not be carried out until now.

The study, published in the journal Nature Geoscience, suggests that the average ice thickness could be considerably higher than previous estimates. In three regions surveyed, the robot sub found that deformed, thickened ice accounted for at least half of and as much as 76 percent of the total ice volume, the researchers say.

Climate skepticism vindicated?

While Antarctica’s ice sheet, that is the land ice, is melting and retreating, the extent of the sea ice has been expanding over the last three winters. This has led some who are skeptical about climate change to suggest that it could be evidence that human-made global warming is not happening. But sea-ice physicist Stefan Hendricks, from the Alfred-Wegener Institute for Polar and Marine Research, based in Bremerhaven, Germany, told me in an interview the new measurements were no reason to doubt climate change is happening.

Ice physicist Hendricks (Foto: Hendricks)

“What our colleagues have shown is that ship-based measurements do not record this really thick ice. That is no surprise to us. It is good that they have found this out, but basically it just tells us that we have to be cautious when it comes to using ship-based data”, Hendricks said.

The sea ice extent in the Antarctic has been growing, while the sea ice in the Arctic, at the northern end of the planet, has decreased dramatically in recent years. Hendricks stresses that the two regions are completely different:

“The Arctic Ocean is surrounded by land, whereas in the Antarctic, the land is in the middle. If the Arctic were not surrounded by land, the ice cover would also be much bigger in winter”, says Hendricks.  The increase in Antarctic sea ice in winter can be partly explained by the wind direction, he adds . Ice grows faster, the thinner it is. If it is blown out from shore, for instance into the Indian Ocean, new ice is created very quickly, according to the ice expert. He also warns against  comparing what happens to the Arctic in summer to what happens at the southern end of the planet in winter:

“If you look at the cycle over the whole year, your will see that the sea ice in the Antarctic also melts almost completely in summer”.

Valuable data, limited application

Still, the German expert says the new ice measurements from the Antarctic are of major importance to our understanding of how sea ice behaves. But he stresses that the ice floes are on the move all the time.  Although the measurements are very exact, the situation is constantly changing ,and the measurements could only be taken at a limited number of spots in what is a huge area of ice.

“The question is how representative is this for the total ice extent? This depends to a very large extent on which ice floe you take. There are large differences between them. The differences are particularly marked if you go further away from land. Close to land, the ice piles up and is deformed and so you get this very thick ice. Further out, you don’t get that”.

The new measurements certainly do not give any reason to be more relaxed about climate warming, says Hendricks.  Increased sea ice could have a cooling effect, as ice reflects heat back into space, whereas the sea water absorbs the heat, exacerbating warming. But given that the ice melts again in summer, that effect would be very slight, says the physicist.

… And the ice continues to melt. (Pic: I. Quaile, Greenland)

While the Arctic is melting twice as fast as the rest of the planet, and protests continue against the race for oil at huge risk to the sensitive environment,  the icy regions around the south pole were long considered immune to climate change. But melting glaciers on the Antarctic Peninsula in recent years sparked doubts in the scientific community about just how stable the western region of Antarctica really is. Earlier this year, I wrote an article on the irreversible melt of the Pine Island glacier on western Antarctica. The huge iceberg that broke off last November has been in the news again, heading for the open sea.

Only the huge icy vastness of Eastern Antarctica still appeared to be safe from the perils of a warming climate. Now experts from Germany’s Potsdam Institute for Climate Impact Research (PIK) have published findings indicating that this too might no longer be the case. In a study published in “Nature Climate Change“, they write that the melting of just a small volume of ice on the East Antarctic coast could ultimately trigger a discharge of ice into the ocean which would result in unstoppable sea-level rise. They are talking about tomorrow or the next decade. Still, the prospect of more irreversible thawing in the Antarctic is a very worrying one.
“Previously, only the West Antarctic was thought to be unstable. Now we know that the eastern region, which is ten times bigger, could also be at risk”, says Anders Levermann, co-author of the study. The findings are based on computer simulations which make use of new, improved data from the ground beneath the ice sheet.PIK scientist Levermann was one of the lead authors of the sea-level section in the latest IPCC report.
“The Wilkes Basin in East Antarctic is like a bottle that is tilted”, says Matthias Mengel, lead author of the new study.”If you take out the cork, the contents will spill out”. At the moment, the “cork” is formed by a rim of ice at the coast. If that were to melt, the huge quantities of ice it holds back could shift and flow into the ocean, raising sea levels by three to four meters. Although air temperatures over Antarctica are still very low, warmer ocean currents could cause the ice along the coast to melt.

Warming oceans: Melting from below (Photo: I.Quaile)

So far, there are no signs of warmer water of this sort heading for the Wilkes Basin. Some simulations suggest though that the conditions necessary for the “cork” to melt could arise within the next 200 years. Even then, the scientists say it would take around 2000 years for sea level to rise by one meter.
According to the simulations, it would take 5,000 to 10,000 years for all the ice in the affected region to melt completely. “But once this has started, the discharge will continue non-stop until the whole basin is empty”, says Mengel. “This is the basic problem here. By continuing to emit more and more greenhouse gases, we could well be triggering reactions today that we will not be able to stop in the future. ” Indeed.
The IPCC report predicts a global sea-level rise of up to 16 centimeters this century. As this could already have devastating impacts on many coastal areas around the globe, any additional factor is of key importance to the calculations. “We have presumably overestimated the stability of East Antarctica”, says Levermann. Even the slightest further increase in sea level could aggravate flooding risks for coastal cities like New York, Tokyo or Mumbai.
At the moment, the largest contribution to Antarctic ice loss and rising sea levels comes from the Pine-Island glacier in West Antarctica. As I mentioned at the start, a huge iceberg, which broke off from the glacier last year, is currently floating into the open waters of the Southern Ocean. French glaciologist Gael Durand from Grenoble University told me in an interview the huge glacier had already reached a point where its continued melting is irreversible, regardless of air temperature or ocean conditions.

AOA campaigers at the German Chancellery

Today, it seems, is World Penguin Day. If you happened to be in the German capital, Berlin, this would have been drawn to your attention by largish “penguins” visiting the embassies of Russia, China and Norway, as well as the German Agriculture Ministry, which, it may surprise you to know, is responsible for the protection of the Antarctic on behalf of the German government

Activists from “The Antarctic Ocean Alliance“, (AOA) made use of the occasion to draw attention to the need to protect the pristine ice region at the south of the world. The background is that Germany will be host to a meeting of the Commission for the Conservation of Antarctic Marine Living Resources (CCALMR) in July this year. The meeting, in Bremerhaven, home of Germany’s Alfred Wegener Institute for polar and marine research,  will be discussing the possible creation of two Marine Protected areas (MPAs) in the Antarctic. The alliance, made up of WWF, Greenpeace, Deepwave, Whale and Dolphin Conservation (WDC) and others, is calling on Germany to play a leading role and on other key countries to support a decision in favour of the protected areas.

Steve Campbell, Campaign Director of the AOA, stressed Germany’s long tradition of scientific polar research and the key role the country could play in Antarctic protection. The alliance stresses that the Southern ocean is under increasing pressure from climate change and resource depletion. The areas the AOA want protected now are described by the campaigners as one of the world’s last wildernesses and an essential “living laboratory” for the planet.

BAS ship James Clark Ross  in the Antarctic
(Courtesy of BAS)

Ice in parts of the Antarctic Peninsula is now melting during the summer faster than at any time during the last thousand years, according to new research results. The scientists have reconstructed changes in the intensity of ice-melt, and the mean temperature on the northern Antarctic Peninsula since AD 1000, based on the analysis of ice cores.

According to the study, published in the journal Nature Geoscience, the coolest conditions and lowest melt occurred from about AD 1410 to 1460, when mean temperature was 1.6 °C lower than that of 1981–2000. Since the late 1400s, there has been a nearly tenfold increase in melt intensity from 0.5 to 4.9%. The warming has occurred in progressive phases since about AD 1460, but the melting has intensified,  and has largely occurred since the mid-twentieth century. The study concludes that  “ice on the Antarctic Peninsula is now particularly susceptible to rapid increases in melting and loss in response to relatively small increases in mean temperature”.

Paul Brown of Climate News Network says the findings explain a series of sudden collapses of ice shelves in the last 20 years, which scientists studying them had not expected. He also quotes the researchers as saying the current melting could lead to “further dramatic events, making the loss of large quantities of ice on the Peninsula more likely, and adding to sea level rise”.

The study is also of interest against the background of the debate going on over the last 20 years on whether the Antarctic would gain mass through extra snow falling and so REDUCE sea level rise, or would lose ice because of higher sea and air temperature and so exacerbate the effect.

The scientists use a 364-metre ice core from James Ross Island to get in insight into both past temperatures and ice melt. Layers in the core show periods when summer snow on the ice cap thawed and then refroze. By measuring the thickness of the layers, they could tell how the history of the melting related to changes in temperature at the site over the last thousand years.

Lead author Dr. Nerilie Abram of the Australian National University and the British Antarctic Survey (BAS) said:  “Summer melting at the ice core site today is now at a level that is higher than at any other time over the last 1,000 years. And whilst temperatures at this site increased gradually in phases over many hundreds of years, most of the intensification of melting has happened since the mid-20th centrtury.

Dr. Robert Mulvaney from the BAS, who led the drilling expedition and co-authored the paper said:  “Having a record of previous melt intensity for the Peninsula is particularly important because of the glacier retreat and ice shelf loss we are now seeing in the area. Summer ice melt is a key process that is thought to have weakened ice shelves along the Antarctic Pensinsula leading to a succession of dramatic collapses, as well as speeding up glacier ice loss across the region over the last 50 years”.

The changes on the Antarctic Peninsula do not necessarily apply to other parts of Antarctica, such as the West Antarctic ice Sheet. Melting is also occurring there and could have an even greater risk of large-scale sea level rise.

Paul Brown from Climate News Network notes “it is not clear that the levels of recent ice melt and glacier loss in West Antarctica are exceptional or are caused by human-driven climate changes.”

Lead author Abram says: “This new ice core record shows that even small changes in temperature can result in large increases in the amount of melting in places where summer tempearatures are near to 0°C, such as along the Antarctic Peninsula, and this has important implications for ice instability and sea level rise in a warming climate”.

I interviewed Andrew Shepherd, Professor of Earth Observation at the British University of leeds, on a major satellite sutdy of the polar ice melt towards the end of last year. It makes interesting listening to complement this latest development:

Interview with Andrew Shepherd

See also:

Polar ice sheets melting faster than ever

Are warming seas changing the Antarctic ice?

Photo gallery: High season for Antarctic researchers

Princess Elisabeth Antarctica, Belgium’s research station
Copyright Ren̩ Robert РInternational Polar Foundation

Regular ice blog followers may remember a recent post including an Interview with Andrew Shepherd from Leeds University, UK, about ice melt in the Antarctic. One of the factors he explained was that increasing precipitation as a result of warming was falling on the East Antarctic ice sheet as snow and so increasing its mass. Although that particular study showed that the Antarctic has indeed been losing ice over the past 20 years, (contrary to popular opinion), increasing snow was balancing this loss to some extent. Now a study published in Nature shows that a lot of the ice increase from this snow is being lost again, because the extra snow puts pressure on the ice, making it flow faster towards the coast.