November 2, 2012
Geologist Proposes New Theory Behind Global Sea Level Rise
April Flowers for redOrbit.com - Your Universe Online
The most recent IPCC report released in 2007 projected a global sea level rise between 0.2 and 0.5 meters by 2100, but current sea level measurements meet or exceed the high end of that range. This suggests a rise of one meter or more by the end of the century.
"What's missing from the models used to forecast sea-level rise are critical feedbacks that speed everything up," says Hay.
Hay will present some of these feedbacks, including Arctic sea ice, the Greenland ice cap, and soil moisture/groundwater mining, at the Geological Society of America meeting on Sunday, November 4, 2012.
Hay is sure there is an Arctic sea ice connection, despite the fact that melting sea ice does not raise sea levels. According to Hay, the sea ice plays a role in the overall warming of the Arctic. This, in turn, leads to ice losses in nearby Greenland and northern Canada. There is an oceanographic effect of releasing more fresh water from the Arctic when the sea ice melts. This is then replaced by inflows of brinier, warmer water from the South. Hay says that this process is a "big heat pump that brings heat to the Arctic."
The problem is that this "heat pump" isn't in any of the current models. The warmer water, which absorbs sunlight rather than reflect it back into space like sea ice does, pushes the Arctic towards more ice-free waters.
The gigantic stores of ice in Greenland and Antarctica melted during the last interglacial period, raising the sea level 10 meters - without any help from human interaction. According to new data, that 10 meter sea level rise took place over centuries.
"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."
The stunning, record-setting melt in the Greenland ice cap last summer brought this possibility home in a big way as 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."
Another disturbing feedback is groundwater mining, which is happening all over the world to mitigate the droughts. That water eventually makes its way into the ocean.
These are all positive feedbacks that are speeding up the changes in climate and sea level rise.
"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."
Image 2 (below): Past and possible future changes in sea level. Map by Emanuel Soeding, Christian-Albrechts University, using U.S. National Oceanic & Atmospheric Administration Etopo2v1 elevation data.