Antarctic Ice Shelves Could Grow in Global Warming
NEW YORK — Global warming could cause Antarctica’s ice shelves to grow instead of shrink, British research concludes.
The new study provides a chilling reminder that climate change can result in surprising and paradoxical effects.
Climate warming in the last century is already melting the small ice shelves of the Antarctic peninsula, a tongue of the southern continent that extends north toward South America. If that warming starts melting much larger ice shelves in the main part of Antarctica, environmentalists and scientists worry that catastrophic environmental changes could result.
But that’s unlikely, according to a paper in the July 31 issue of the scientific journal Nature.
“If anything, they’re going to get thicker,” said Keith Nicholl, an oceanographer with the British Antarctic Survey.
Ice shelves are layers of ice up to hundreds of feet thick that extend seaward from Antarctica’s continental glaciers, covering bays and inlets year-round.
To determine whether Antarctica’s major ice shelves are vulnerable to climate change, scientists from the British Antarctic Survey drilled a hole through the Ronne Ice Shelf in the Weddell Sea. Instruments lowered into the water beneath the shelf showed that during most of the year, a warm current slides underneath the ice, melting it at a rate of about 15 feet a year.
But during the summer, that current disappears and the melting stops. Presumably, future climate warming could have the same effect that summer weather does today.
“If you reduce the circulation beneath the ice shelf, then you reduce the melting,” Nicholl said.
Paradoxically, the warm water current is created only in winter, when water freezes at the shelf’s edge. The freezing removes fresh water from the ocean’s surface layer and turns it into sea ice, leaving behind a denser salty brine. That salty water slides as a current under the ice shelf, melting it from beneath.
If global warming decreases the production of sea ice, Nicholl hypothesizes, then the current would slow down. He predicts that a 5-degree Fahrenheit warming expected in the next century would decrease the melting rate about 10%, causing the Ronne Ice Shelf to grow slightly.
“It makes sense to me,” said J.R. Toggweiler, director of the Geophysical Fluid Dynamics Laboratory in Princeton, N.J.
But Nicholl’s study only applies as long as the present currents continue. A big enough warming could change the Southern Ocean’s circulation pattern altogether, exposing the shelf ice to much warmer water.
“You can’t discount changes in the circulation of the water that would render all of this moot,” Toggweiler said.
