Shrinking Arctic ice area is just the tip of the iceberg

Like icebergs, much of the mass of Arctic ice lies under the surface, making studying its thickness important, as well as the area it covers. Credit: Florida State University

Like icebergs, much of the mass of Arctic ice lies under the surface, making studying its thickness important, as well as the area it covers. Credit: Florida State University

A sheer white glacial mountain apparently floating on the sea emerges from the freezing mists. A lone lookout cries “Iceberg!”, stirring the crew into panic, before the stomach-churning sound of ripping metal sends them to the lifeboats. It’s a familiar scene from the TV and movies, and one where the main threat comes because eight-ninths of a typical iceberg lies below the waterline. While sea ice formed from ocean water is much thinner than such glacier ice, its thickness also lies mostly beneath the surface. Consequently, knowing that thickness is “perhaps the most basic measure of how the ice is responding to climate change”, according to the University of Colorado’s James Maslanik. Although it’s possible to track the area that the Arctic ice cap covers from space, knowing the depth it reaches is harder. “While the European Space Agency has just launched Cryosat-2 to measure thickness, the US no longer has a satellite operating that is capable of directly measuring ice thickness from space,” the scientist explained.

To tackle this problem, Maslanik and Colorado colleagues Julienne Stroeve, Charles Fowler, and William Emery have turned to assessing how many summer melt periods the ice is surviving. Maslanik says not only is this closely linked to ice thickness, it also reflects the influence of many climate- and weather-related factors. Ice that survives one summer melt is called “multi-year ice”. In a Geophysical Research Letters paper soon to be published, they find that multi-year ice makes up 45 per cent of the total Arctic ice cover in 2011, down from about 75 per cent in the mid 1980s. The proportion of ice older than five years fell from 50 per cent of all ice that has survived more than one summer to 10 per cent in the same period.

“The work of our Colorado group and other researchers clearly shows extreme decreases in the area of the Arctic Ocean covered by the oldest and thickest sea ice types,” Maslanik told Simple Climate. “This loss has accelerated in recent years, and while we continue to search for factors such as natural variability that could account for the changes, the effects of large-scale warming in the Arctic, including changes in the Arctic Ocean itself, are the most likely drivers for the loss in the old sea ice.” Read the rest of this entry »

Retreating Arctic coasts show need for careful science

A scientist standing in front of an ice-rich permafrost exposure in the coastal zone of Herschel Island, Yukon Territory, Canada. These ice bodies in the permafrost are rapidly eroded by the sea in the coastal zone. Photo: Michael Fritz

A scientist standing in front of an ice-rich permafrost exposure in the coastal zone of Herschel Island, Yukon Territory, Canada. These ice bodies in the permafrost are rapidly eroded by the sea in the coastal zone. Photo: Michael Fritz

A decade-long study into the state of coasts in the Arctic has revealed that climate change is accelerating erosion there. The “State of the Arctic Coast 2010” report says that average erosion rates see coasts retreat half a metre per year, while some areas lose more than eight metres annually. That’s because, as sea-ice melts around the North Pole, larger exposed ocean areas enable the wind to whip up waves that damage the coastline more easily. However Hugues Lantuit, one of the editors of the report, underlines that without this specific scientific effort it would be hard to separate these effects from normal coastline erosion.

“The coast has always eroded, and there were always spectacular features in the coastal zone,” explained Lantuit, who works at the Alfred Wegener Institute for Polar and Marine Research in Potsdam, Germany. “In that sense, it is difficult to grasp the issue of climate change with the human eye. Data is necessary to complement it and to pinpoint to what is truly an impact of the climate and what isn’t. The climate has been warming dramatically in the Arctic, and the sea ice is retreating. The major challenge for us scientists is to quantify and link with precision the processes at work in the area. To do this, the human eye is often not enough.” Read the rest of this entry »

Ice melt poses dual sea rise and water access threat

Ice from Arctic Canada, like this small unnamed valley glacier and the Kaskawulsh glacier in the background in Saint Elias Mountains, Yukon Territory, will be among the largest contributors to sea level rise as ice caps and glaciers across the world melt in the 21st century. Credit: Christian Schoof.

Ice from Arctic Canada, like this small unnamed valley glacier and the Kaskawulsh glacier in the background in Saint Elias Mountains, Yukon Territory, will be among the largest contributors to sea level rise as ice caps and glaciers across the world melt in the 21st century. Credit: Christian Schoof.

Around one-fifth of the total volume of ice held in ice caps and glaciers will melt by 2100, adding around 12 cm to sea levels and threatening very low-lying coastal regions. That’s according to the latest simulations from Valentina Radić of the University of British Columbia, Canada and her US-based colleague Regine Hock from the University of Alaska, Fairbanks. “The problem will be floods and storm surges which also will be higher if the sea level is higher than today,” Radić told Simple Climate. She and Hock used detailed glacier measurements to model how the world’s ice will respond to predicted temperature changes. Their results, published in leading journal Nature Geoscience last Sunday, also show that Europe and New Zealand look set to lose around three-quarters of their glacier volume, impacting water supplies.

So far, there have been few predictions of what will happen to the world’s ice this century, and there has been large disagreement among those that have been produced. The resulting sea-level rise predictions range from a minimum of 5 cm to an extreme maximum of 36 cm. The issue, Radić explained, is that there are surprisingly few measurements of glaciers to begin predictions from. “The World Glacier Inventory today covers approximately 40 percent of the total ice area,” she said. “For the remaining 60 percent we still do not know how many glaciers there are, what is their surface area, elevation range, and so on.”

Worse still, less than one percent of the world’s glaciers have been measured for mass balance – the difference between the mass a glacier gains through the accumulation of snow, and what it loses – over the long term. “Observations of glacier mass balance are extremely important for the modellers,” Radić explained. “To reassure ourselves that the models are performing well, we need to validate their results with the ‘real world’. A lack of these observations presents a major obstacle for modelling of future glacier volume changes.” Read the rest of this entry »

Climate-driven species creep hangs in the balance

Studies of moss campions in North America have demonstrated that climate change may create tipping points in populations. Credit: Daniel Doak

Studies of moss campions in North America have demonstrated that climate change may create tipping points in populations. Credit: Daniel Doak

There is overwhelming evidence that many species have shifted the geographical ranges they live in over recent decades, with some actually becoming more widespread. However, adverse effects of climate change could still await these species, say University of Wyoming’s Daniel Doak and William Morris at Duke University in Durham, North Carolina.

Their research shows competing influences are holding the southern range limit of two Arctic and alpine plants in place, while warming forces the northern limit further north. However, their temperature-driven spread may ultimately prove short-lived, Doak warns. “Up to a point we may see little effect of warming for many organisms,” he says. “But past a climatic tipping point, the balance of opposing effects of warming will likely cease, leading to subsequent rapid declines in populations.” Read the rest of this entry »

Saturday round-up: Methane menace?

Natalia Shakhova, who led a series of month-long expeditions on icebreakers in the Arctic monitoring methane levels. Credit: Todd Paris, University of Alaska, Fairbanks.

Natalia Shakhova, who led a series of month-long expeditions on icebreakers in the Arctic monitoring methane levels. Credit: Todd Paris, University of Alaska, Fairbanks.

Frozen undersea terrain in the Arctic is warming up and bubbling out massive, previously overlooked, amounts of the greenhouse gas methane. Around eight million tonnes of methane is being produced annually  – roughly equivalent to the total amount of methane that had been thought to be emitted by all the world’s seas.

“Remobilization to the atmosphere of only a small fraction of the methane held in East Siberian Arctic Shelf (ESAS) sediments could trigger abrupt climate warming,” write Natalia Shakhova and colleagues in the journal Science. “It is believed that sub-sea permafrost acts as a lid to keep this shallow methane reservoir in place. The permafrost lid is clearly perforated, and sedimentary methane is escaping to the atmosphere.”

Shakhova and fellow scientists at the University of Alaska, the Russian Academy of Sciences and Stockholm University conducted studies on ice-breaking ships between 2003 and 2008. This was the largest study of methane emissions in the ESAS area ever conducted. The researchers found that most of the area – reaching halfway across the Northern Russian coast – contained more methane than would normally be possible. The team also recorded bubble clouds emerging from the sea. “Taken together, the observations demonstrate that the ESAS—the world’s largest continental shelf sea—is perennially laden with methane all the way up to the sea surface,” the researchers write.

The sea surface above the East Siberian Arctic Shelf is full of ice and bubbles. Sonar is the only way to detect the vast clouds of methane bubbles rising from the seafloor. Photo courtesy of Igor Semiletov, University of Alaska Fairbanks

The sea surface above the East Siberian Arctic Shelf is full of ice and bubbles. Sonar is the only way to detect the vast clouds of methane bubbles rising from the seafloor. Photo courtesy of Igor Semiletov, University of Alaska Fairbanks

While the researchers say that the additional amount of methane produced is large, it is not alarming. With the ESAS being hard to access and measure, it is unclear whether these emissions have begun recently or have been going on for some time. However, they are likely to be accelerated by warming seas. “To discern whether this extensive methane venting over the ESAS is a steadily ongoing phenomenon or signals the start of a more massive methane release period, there is an urgent need for expanded investigations,” the researchers write.

Meanwhile, this week New Scientist reported on a recent Geophysical Research Letters paper showing that ice flow out of the Arctic into a channel between Canada and Greenland reached highs in 2007 and 2008. Ronald Kwok of the Jet Propulsion Laboratory in California, together with researchers from the Danish Meteorological Institute and the University of Copenhagen looked at flows into the Nares Strait between 1997 and 2009. Looking at data from satellites, they noted ice arches forming in two places along the strait usually stop these flows, but one failed to form in 2007, and only briefly stopped the ice in 2008.

The Nares Strait contains some of the thickest ice in the Arctic. The arches that stop it from flowing usually form in late autumn and early winter. They are typically made up from ice that has flowed through earlier in the year, fixed together with more recently frozen material. However, the early year ice flows have been melting to produce ever smaller lumps in the later period of the survey, meaning that it’s harder to form arches. “If there is a decreased likelihood of arch formation as the ice cover becomes thinner and weaker due to warming, there is the potential for the Nares Strait to shift to a higher flow,” Kwok and colleagues write.

Saturday round-up: Southwest Western Australia suffering unrivalled drought?

Tas van Ommen collecting an ice core at Law Dome in Antarctica Credit: Joel Pedro

Tas van Ommen collecting an ice core at Law Dome in Antarctica Credit: Joel Pedro

Australian researchers say that snowfall records in Antarctica show that the current drought south of Perth is unlikely to have been matched in 750 years, and possibly even longer. To reach this conclusion, Tas van Ommen and Vin Morgan used measurements of cylindrical samples of ice drilled from the Law Dome. This small icecap on the coast of East Antarctica is south of the south-west Western Australia (SWWA) region that has been affected by a 15-20% decline in winter rainfall since 1970. It’s hard to understand the drought’s full historical significance, due to the relatively small amount of direct rainfall information, say van Ommen and Morgan in a Nature Geoscience paper published online last Sunday. “Local records commence only around the start of the twentieth century,” they write.

Analysing ice core information to give weather patterns showed that declining rainfall in SWWA corresponded with increasing snowfall at the Law Dome. There is also a clear link between smaller changes in rain and snow at the two locations, the Australian Antarctic Division and Antarctic Climate and Ecosystems Cooperative Research Centre scientists say. So, the ice core data can tell us how unusual the SWWA weather is. The increase in snowfall at the Law Dome during the period of the drought is the largest in 750 years, van Ommen and Morgan find. They calculate that if environmental conditions had stayed the same, such a change in rain and snowfall should happen just once in at least 5,400 years. “The recent post-1970 anomaly in Law Dome precipitation lies outside the envelope of natural variability and supports the hypothesis of [man-made climate change],” the scientists write.

Meanwhile, amid controversy about how fast glaciers are receding elsewhere, another Nature Geoscience paper, published in the February issue, gives an improved estimate of the status of glaciers in Alaska. The collaboration of scientists from France, the USA and Canada suggests they are melting more slowly than previously thought, contributing around a third less to sea level rises than previously estimated. They say that thinning in other glacial regions could have been been overestimated by a similar amount.

The team’s calculations are based on the height of the glaciers, comparing data from 1962 maps with satellite maps from 2006. They say that using satellite data, rather than manual surveys as other groups have, gives them a more detailed picture of the situation. It also shows that if glaciers are covered with debris, they melt more slowly, as they are insulated from the warmth of the atmosphere. This is a factor overlooked by previous studies, they write. Their estimates suggest that between 1962 and 2006, Alaskan glaciers lost around 42 cubic kilometres of water per year, which raised sea levels by around 0.12 mm per year.