State of the Antarctic
New SCAR report shows continent undergoing major changes
Posted December 18, 2009
A week before world leaders sat down for a major climate conference in Copenhagen this month, an international scientific body released the first comprehensive report on the current state of Antarctica’s climate and its relationship to the rest of the globe.
The report from the Scientific Committee on Antarctic Research (SCAR), Antarctic Climate Change and the Environment (ACCE), pulls together the latest research from 100 scientists from eight countries.
The report suggests that the West Antarctic Ice Sheet, in particular, will contribute significantly to sea level rise by the end of the century. The scientists predict a total sea level rise of 1.4 meters by 2100, with “tens of centimeters” coming from the glaciers that drain West Antarctica.
Such a rise in global oceans would likely flood coastal regions and low-lying areas, from New York City to Bangladesh.
The 2007 Intergovernmental Panel on Climate Change (IPCC) assessment report projected a sea-level rise of between 18 and 59 centimeters by century’s end. However, some criticized that report because it really only accounted for changes in the Arctic, largely ignoring Antarctica and the Southern Ocean that encircles the world’s coldest and driest continent.
Paul Mayewski, one of the nine editors for the SCAR report and director of the Climate Change Institute at the University of Maine, said the polar scientific community had discussed such a document for years, but only recently has there been the momentum to pull together the 555-page, wide-ranging report.
“There has been an explosion in Antarctic information and data gathering, really only in the last three or four years, and I think the time has only been right in the last three or four years,” he said. “We’re going to be in plenty of time for the next IPCC.”
Robert Bindschadler, chief scientist of the Hydrospheric and Biospheric Sciences Laboratory at NASA’s Goddard Space Flight Center and another editor on the SCAR report, said that until recently the Antarctic wasn’t changing as rapidly as the Arctic. That’s no longer the case.
“The fact that changes are happening faster and faster is the primary motivation to get a benchmark in place,” said Bindschadler, only just returned from Antarctica after his most recent fieldwork to test equipment and techniques for an upcoming project to Pine Island Glacier, where West Antarctica is most quickly hemorrhaging ice into the ocean.
The key message from the report, Bindschadler said, is that “the ice is changing. The ice sheet is changing faster than we ever expected to witness ice sheets changing in our lifetimes, quite honestly.”
Ozone hole drives changes
One finding from recent years that received prominence in the SCAR report concerned the effects of the ozone hole on the Antarctic climate.
Unlike the coastal areas, particularly in West Antarctica, the interior of Antarctica has cooled slightly, according to polar researchers cited in the SCAR report. That’s because the ozone hole over the Southern Hemisphere has cooled the stratosphere, the layer of the atmosphere above the troposphere that people inhabit.
However, the ocean around the continent and regions to the north are warming. The temperature differential has caused atmospheric circulation to intensify around Antarctica, effectively shielding much of the continent from the intrusion of warmer air to the north.
But as the ozone hole heals, those westerly winds will ease, allowing warmer air to mix more easily into the Antarctic atmosphere. The SCAR report estimates a continent-wide temperature increase of 3 degrees Celsius by 2100.
“This is what has happened in the northern hemisphere. You have a relatively warm Arctic and a warm low- to mid-latitudes, and the westerlies have slowed down,” Mayewski said. “The big questions for the Antarctic are when will it happen and how fast will it happen.”
Mayewski said based on climate records, particularly from ice cores, that sudden shifts in position and strength of the westerlies have created many of the abrupt climate changes of the past.
Mayewski said: “The implicit but not explicit statement in my mind in this report is the fact that we could very well be headed for not a linear change in the westerlies, but an abrupt change in the westerlies,” he said. “If we experience a very abrupt weakening of the westerlies — we can show that it happened in the past — we could very well have accelerated levels of warming in Antarctica.”
A recent paper in the journal Geophysical Research Letters by Marco Tedesco at City College of New York and Andrew Monaghan at the National Center for Atmospheric Research in Boulder, Colo., suggested that a 30-year record low in Antarctic snowmelt during the 2008-09 austral summer was likely due to intensified westerlies and El Niño-Southern Oscillation (ENSO). ENSO is a periodic change in oceanic and atmospheric conditions in the tropical Pacific Ocean that has far-reaching effects on weather around the world.
The authors suggest, in step with the SCAR report, that the healing of the ozone hole will eventually ease the westerlies, resulting in more warming in Antarctica. The SCAR report lists Monaghan as one of its 100 authors.
Feedback in the Antarctic
The warming would also likely affect the extent of sea ice cover around Antarctica, which the SCAR report says has actually increased 10 percent in extent since 1980 due to the stronger winds. Sea ice effectively doubles the size of Antarctica in the winter.
Again, as the ozone hole closes and the winds decrease, sea ice would diminish, by as much as 30 percent by the end of the century, according to the report.
Around the Antarctic Peninsula, where regional warming has been on a record-setting pace, sea ice has declined significantly. Work by U.S. Antarctic Program scientists in the region has found that the increase is about 6.5 degrees Celsius in the winter since the 1950s, rising more than five times faster than the global average. The life cycle of winter sea ice, on average, has dropped by three months per year, meaning it forms later and melts earlier. Year-round sea ice has virtually disappeared.
Mayewski noted that the disappearance of sea ice creates a positive feedback loop for warming. The white ice-covered ocean reflects the solar heat, while the darker ocean more readily absorbs the heat and warms up more, which causes more sea ice to disappear. That’s what is currently happening in the Arctic.
“The same thing is going to happen around West Antarctica, and any coastal areas around Antarctica, so those regions will warm much more than the mean or average of 3 degrees centigrade,” he said.
Bindschadler noted that it’s also deep, warmer ocean water coming up onto the continental shelf — where ice, bedrock and water meet — that’s driving the changes at the margins of the ice sheet.
“That to me is a harbinger. Ice loss around the edges of the ice is what is becoming the norm now [more] than the exception,” he said.
The SCAR report also discusses the effects of a warming Antarctic on the continent’s biology. For instance, sea ice is a key habitat where sea algae grow. Shrimplike krill graze on the algae, and larger critters like penguins and whale feed on the krill. A loss of sea ice, which is also a winter habitat for species like the Adélie penguin, could create a ripple effect throughout the food chain.
“We see very clearly how the atmosphere is linked to the ocean, and how the ocean is linked to the ice sheet, and how the biological component is dependent on all three of those things,” Bindschadler said. “It’s a very tightly coupled system there.”
Nate Biletnikoff, Environmental Engineering manager for Raytheon Polar Services, the prime contractor to the NSF, said the report will be a valuable resource for national Antarctic programs evaluating human environmental impacts to the continent.
“Understanding Antarctica’s environment and biologic communities in their present state and establishing a baseline in which to compare [future changes] is the primary component in accurately assessing human activities’ effects on the environment,” he said
More work ahead
The SCAR report uses only scientific papers that have appeared in peer-reviewed journals, many from U.S.-based researchers. The report represents an immense amount of National Science Foundation-funded research, said Mayewski, who led an international effort, the 21-nation International Trans Antarctic Scientific Expedition (ITASE), to collect shallow ice cores across Antarctica to reconstruct climate over the last 200 to 1,000 years.
Both Mayewski and Bindschadler said there has been tremendous progress over the last several years in getting a better handle on processes that drive climate change in Antarctica. But both also cautioned that scientists are far from being able to create climate models that can accurately predict such as future ice loss and sea level change.
“Science always lusts for more information,” Mayewski said. “Antarctica is an amazing treasure trove of information because it is the world’s largest repository of ice cores. It is such a dynamic system. It is so large; it is going to take us a long time to really understand the kind of details we need to bring to bear to understand how the Antarctic system operates.”
Bindschadler said he believes the polar science community is at least 20 years away from understanding the system well enough to account for all the forces at work in the ocean-atmosphere-ice system. That’s partly because the places where scientists need to go for their work is still inaccessible or difficult to reach.
“The specific places where we need to get the measurements are even the toughest of the tough locations,” said Bindschadler, whose fieldwork at Pine Island Glacier in 2011-12 will be the culmination of years of planning, with construction of a special field camp at the extreme limits of the USAP logistics chain to support the project.
“We’re going to have to solve that,” he added. “We’re going to have to commit the resources to make those measurements, or we simply will not achieve the predictive skill people are calling for as our necessary objective.”
NSF-funded support in this article: Paul Mayewski, University of Maine, Award No. 0837883; Robert Bindschadler, NASA/Goddard Space Flight Center, Award No. 0732906.
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