Study Uncovers Why Sea Levels are Rising Faster Than Predicted

According to a press statement released by GSA, "During the last interglacial period , sea levels rose to 10 meters due to the melting of ice in Greenland and Antarctica. Humans were not responsible for this drastic alteration in the climate." 

But according to Bill Hay, a geologist at the University of Colorado, new data suggests that the sea-level rise in the oceans took place over a few centuries. It is seen that the sea levels are rising faster than expected from global warming.

The last official Intergovernmental Panle on Cliamte Change (IPCC) report in 2007 projected a global sea level rise between 0.2 and 0.5 meters by the year 2100. But current sea-level rise measurements meet or exceed the high end of that range and suggest a rise of one meter or more by the end of the century.

Similarly, a recent research that was led by Kenneth G. Miller, professor of earth and planetary sciences in the School of Arts and Sciences at Rutgers University, reached the same conclusion by studying rock and soil cores in Virginia, Eniwetok Atoll in the Pacific and New Zealand. They looked at the late Pliocene epoch, 2.7 million to 3.2 million years ago, the last time the carbon dioxide level in the atmosphere was at its current level, and atmospheric temperatures were 2 degrees C higher than they are now. He highlighted the sensitivity of the earth's great ice sheets to temperature change, suggesting that even a modest rise in temperature results in a large sea-level rise.  

"What's missing from the models used to forecast sea-level rise are critical feedbacks that speed everything up," says Hay.

"There is an Arctic sea ice connection," says Hay, "despite the fact that melting sea ice which is already in the ocean does not itself raise sea level. Instead, it plays a role in the overall warming of the Arctic, which leads to ice losses in nearby Greenland and northern Canada."

Hay explains the presence of an oceanographic effect of releasing more fresh water from the Arctic, which is then replaced by inflows of brinier, warmer water from the south.

"So it's a big heat pump that brings heat to the Arctic," says Hay. "That's not in any of the models."

The study states that the warmer water pushes the Arctic towards more ice free waters, which take up sunlight rather than reflect it back into space like sea ice does. More the amount of open water, greater is the amount of heat that is being trapped in the Arctic waters and the warmer things can get.

"You can lose most of the Greenland ice cap in a few hundred years, not thousands, just under natural conditions," says Hay. "There's no telling how fast it can go with this spike of carbon dioxide we are adding to the atmosphere."

This possibility was brought home this last summer as Greenland underwent a stunning, record-setting melt. The ice streams, lubricated by water at their base, are speeding up.

Hay notes, "Ten years ago we didn't know much about water under the Antarctic ice cap. But it is there, and it allows the ice to move -- in some places even uphill due to the weight of the ice above it."

"It's being squeezed like toothpaste out of a tube," explains Hay. "The one thing that's holding all that ice back from emptying into the sea is the grounded ice shelves acting like plugs on bottles at the ends of the coastal glaciers. Nobody has any idea how fast that ice will flow into the oceans once the ice shelves are gone."

"You would expect negative feedbacks to creep in at some point," says Hay. "But in climate change, every feedback seems to go positive." The reason is that Earth's climate seems to have certain stable states. Between those states things are unstable and can change quickly. "Under human prodding, the system wants to go into a new climate state," he adds.

Hay will be presenting some of these feedbacks in a talk on Nov. 4, at the meeting of The Geological Society of America in Charlotte, North Carolina, USA. The research data involves Arctic sea ice, the Greenland ice cap, and soil moisture and groundwater mining.