Washington, November 2: A US researcher seems to have found the reason as to why sea level rise caused by global warming is double that of the estimates.
The last official 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.
“What’s missing from the models used to forecast sea-level rise are critical feedbacks that speed everything up,” says University of Colorado geologist Bill Hay.
One of those feedbacks involves Arctic sea ice, another the Greenland ice cap, and another soil moisture and groundwater mining.
“There is an Arctic sea ice connection,” says Hay, adding 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.
When sea ice melts, Hay explains, there is 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.”
That warmer water pushes the Arctic toward more ice-free waters, which absorb sunlight rather than reflect it back into space like sea ice does. The more open water there is, the more heat is trapped in the Arctic waters, and the warmer things can get.
Then there are those gigantic stores of ice in Greenland and Antarctica. During the last interglacial period, sea level rose 10 meters due to the melting of all that ice-without any help from humans.
New data suggests that the sea-level rise in the oceans took place over a few centuries, according to Hay.
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.
Another missing feedback is the groundwater being mined all over the world to mitigate droughts. That water is ultimately added to the oceans.
All of these are positive feedbacks speeding up the changes in climate and sea-level rise.
The study will be presented at the meeting of The Geological Society of America in Charlotte, North Carolina, USA. (ANI)