Warming Oceans Will Melt Glaciers Quicker than Expected

Jennifer Welsh, LiveScience Yahoo News 3 Jul 11;

Ice sheets simmering in warmer ocean waters could melt much quicker than realized. New research is suggesting that as oceans heat up they could erode away the ice sheets much faster than warmer air alone, and this interaction needs to be accounted for in climate change models.

"Ocean warming is very important compared to atmospheric warming, because water has a much larger heat capacity than air," study researcher Jianjun Yin, of the University of Arizona, said in a statement. "If you put an ice cube in a warm room, it will melt in several hours. But if you put an ice cube in a cup of warm water, it will disappear in just minutes."

The researchers studied 19 state-of-the-art climate models and saw that subsurface ocean warming could accelerate ice-sheet melting over the next century, resulting in greater sea level rise that could exceed 3 feet (1 meter). Glaciers in Greenland and Antarctica will melt at different rates, though. [In Photos: Glaciers Before and After]

Different strokes for different coasts

Given a mid-level increase in greenhouse gases, the ocean layer about 650 to 1,650 feet (200 to 500 meters) below the surface would warm, on average, about 1.8 degrees Fahrenheit (1 degree Celsius) by 2100, the researchers found.

The actual warming in different regions could differ significantly, though. They found that temperatures of subsurface oceans along the Greenland coast could increase as much as 3.6 F (2 C) by 2100, but along Antarctica would warm less, only 0.9 F (0.5 C).

"No one has noticed this discrepancy before — that the subsurface oceans surrounding Greenland and Antarctica warm very differently," Yin said. The discrepancy is caused by different currents in the ocean: The Gulf Stream will send warmer waters toward Greenland, while the Antarctic Circumpolar Current blocks some of the warmer waters from reaching Antarctica.

Warmer waters = melting ice

This drastic increase in ocean warming will have a substantial impact on how quickly the polar ice sheets melt, as warmer waters will erode away the ice sheets below the surface. This is on top of increased melting from warmer air in the region. As the glaciers' underwater support structures melt, they lose chunks of ice, which become icebergs.

"This does mean that both Greenland and Antarctica are probably going melt faster than the scientific community previously thought," study researcher Jonathan Overpeck, also of the University of Arizona, said in a statement. "We could have sea level rise by the end of this century of around 1 meter [more than 3 feet] and a good deal more in succeeding centuries."

Previous estimates had projected sea levels to rise by anywhere between 1.5 and 6.5 feet (0.56 and 2 m), and in 2011 a study by Eric Rignot, of the University of California at Irvine, and others projected that sea level rise would reach 12.6 inches (32 centimeters) by 2050 alone. Overpeck and Yin's study adds to the evidence that sea level rise by the end of the century will be near the high end of these projects.

The study was published today (July 3) in the journal Nature Geoscience.

Warming ocean could melt ice faster than thought
Randolph E. Schmid AP Yahoo News 3 Jul 11;

WASHINGTON (AP) — Warming air from climate change isn't the only thing that will speed ice melting near the poles — so will the warming water beneath the ice, a new study points out.

Increased melting of ice in Greenland and parts of Antarctica has been reported as a consequence of global warming, potentially raising sea levels. But little attention has been paid to the impact of warmer water beneath the ice.

Now, Jianjun Yin of the University of Arizona and colleagues report the warming water could mean polar ice melting faster than had been expected. Their report was published Sunday in the journal Nature Geoscience.

While melting floating ice won't raise sea level, ice flowing into the sea from glaciers often reaches the bottom, and grounded ice melted by warm water around it can produce added water to the sea.

"Ocean warming is very important compared to atmospheric warming because water has a much larger heat capacity than air," Yin explained. "If you put an ice cube in a warm room, it will melt in several hours. But if you put an ice cube in a cup of warm water, it will disappear in just minutes."

In addition, Yin explained, if floating ice along the coastal areas melts it will allow the flow of glaciers to accelerate, bringing more ice into the seas.

"This mean that both Greenland and Antarctica are probably going to melt faster than the scientific community previously thought," co-author Jonathan T. Overpeck said in a statement.

Overpeck, co-director of the University of Arizona's Institute of the Environment, said: "This paper adds to the evidence that we could have sea level rise by the end of this century of around 1 meter and a good deal more in succeeding centuries."

The subsurface ocean along the Greenland coast could warm as much as 3.6 degrees Fahrenheit (2 Celsius) by 2100, the researchers reported. The warming along the coast of Antarctica would be somewhat less, they calculated, at 0.9 degree F (0.5 C).