Scientists cautious about ability to predict sea-level rise from WAIS
Posted July 10, 2009
David Holland is an expert at modeling climate processes, yet even he is skeptical that numerical models will be able to project future sea level rise accurately because only so much of the Earth system is observable by scientists.
“It’s not clear yet that it’s predictable,” said Holland, a co-principal investigator on a project to study the ice and ocean interaction below the ice shelf that fronts Pine Island Glacier. “This is an incredibly hard problem.”
The United Nations Intergovernmental Panel on Climate Change (IPCC) predicted in its 2007 report that sea level could creep up by 18 to 59 centimeters by century’s end. But those estimates didn’t take into account the ice sheets in Antarctica and Greenland because so much uncertainty surrounds how recent dramatic changes in these vast reservoirs of ice will evolve through this century.
In particular, Pine Island Glacier (PIG) and nearby Thwaites Glacier are speeding up, with the capacity to drain a third of the West Antarctic Ice Sheet. Another third flows into the Ronne Ice Shelf, with roughly another third draining into the largest of all ice shelves, the Texas-sized Ross Ice Shelf.
“[Pine Island] is the third that I think everybody is worried about. There isn’t a big ice shelf holding it back,” noted Robert Bindschadler , principal investigator for the PIG study, a project scheduled to begin making direct observations of PIG in 2011-12.
Many experts have said they expect the oceans to rise at least a meter by 2100, though not uniformly around the world, with some predicting heavy flooding along the east coast of the United States and Canada as ocean currents change. In another recent scenario posited by scientists, the change in mass in the southern hemisphere as the West Antarctic Ice Sheet melted would drive more water toward North America as gravity strengthened in the northern hemisphere.
Director of the Center for Atmosphere Ocean Science at New York University , Holland and his colleagues hope to shrink some of the uncertainty by observing what happens below the PIG ice shelf as deep, warm ocean water floods onto the continental shelf below.
What’s the circulation doing? How often does the warm water intrude on the shelf? What are the melt rates? Those are the sorts of questions the scientists hope to answer with a small array of ocean profilers developed by Tim Stanton’s team in the Oceanography Department at the Naval Postgraduate School .
“There are great implications for sea-level rise. We really do have to understand this problem,” Stanton said. “It’s pretty intriguing that this group with different interests has been brought together to address this really knotty problem.”
What polar researchers suspect is that increased intensity in westerly winds around Antarctica is helping draw that deep ocean water onto the continental shelf in Pine Island Bay. Other scientists farther north along the Antarctic Peninsula have observed a similar phenomenon as part of the Palmer Long Term Ecological Research program. [See related story: Getting Warmer.]
A number of scientists believe the disruption of ozone in the stratosphere may be responsible for the change in circulation lower in the atmosphere over Antarctica. In theory, the predicted recovery of the ozone layer later this century could ease the westerly winds and their effect on ocean circulation.
Holland is also cautious on that account. “The atmosphere is a very chaotic, delicate beast, so whether or not that is predictable is a question,” he said.
Bindschadler is optimistic that the upcoming expedition will fill in important gaps of knowledge about ocean and ice interaction.
“What we can say confidently is that we know so little about this environment that we’re sure to discover something. That’s the exciting thing. We know we’re going to discover something about a very important process about how climate is changing on Earth, right now and affecting this generation and the next generation and the next generation,” he said.
“This is science in the here and now,” he added. “This stuff really matters to … people who are living on this planet and to the nearly half of the world’s population that are living close to the coast — this matters. … It’s probably the most immediately relevant science I’ve done in my career.”