EnviroLink Forum

http://www.nasa.gov/topics/earth/featur ... -melt.html

For several days this month, Greenland's surface ice cover melted over a larger area than at any time in more than 30 years of satellite observations. Nearly the entire ice cover of Greenland, from its thin, low-lying coastal edges to its two-mile-thick center, experienced some degree of melting at its surface, according to measurements from three independent satellites analyzed by NASA and university scientists.

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http://thinkprogress.org/climate/2007/0 ... es-hansen/



Rahmstorf (2007) has noted that if one uses the observed sea level rise of the past century to calibrate a linear projection of future sea level, BAU warming will lead to a sea level rise of the order of one meter in the present century. This is a useful observation, as it indicates that the sea level change would be substantial even without the nonlinear collapse of an ice sheet. However, this approach cannot be taken as a realistic way of projecting the likely sea level rise under BAU forcing. The linear approximation fits the past sea level change well for the past century only because the two terms contributing significantly to sea level rise were (1) thermal expansion of ocean water and (2) melting of alpine glaciers.


Under BAU [business as usual] forcing in the 21st century, the sea level rise surely will be dominated by a third term: (3) ice sheet disintegration. This third term was small until the past few years, but it is has at least doubled in the past decade and is now close to 1 mm/year, based on the gravity satellite measurements discussed above. As a quantitative example, let us say that the ice sheet contribution is 1 cm for the decade 2005–15 and that it doubles each decade until the West Antarctic ice sheet is largely depleted. That time constant yields a sea level rise of the order of 5 m this century. Of course I cannot prove that my choice of a ten-year doubling time for nonlinear response is accurate, but I am confident that it provides a far better estimate than a linear response for the ice sheet component of sea level rise under BAU forcing.


An important point is that the nonlinear response could easily run out of control, because of positive feedbacks and system inertias. Ocean warming and thus melting of ice shelves will continue after growth of the forcing stops, because the ocean response time is long and the temperature at depth is far from equilibrium for current forcing. Ice sheets also have inertia and are far from equilibrium: and as ice sheets disintegrate their surface moves lower, where it is warmer, subjecting the ice to additional melt. There is also inertia in energy systems: even if it is decided that changes must be made, it may require decades to replace infrastructure.


Only time will tell. Will we see more warm times over the summit or will this continue to be a rare event. Below is acceleration and velocity for 5 meters sea level rise by 2100. Keep in mind the equation used is for constant acceleration. Both Hansen and Rahmstorf are talking non linear terms of acceleration.



viewtopic.php?f=3&t=19573

A = .117cm/year acceleration = 1.17mm/year*2 = 11.7mm/decade*2 acceleration average over the next 88 years.
velocity = 10.596cm/year velocity = 4.17 inches/year = 41.7 in./decade

NY Times:

"On average, about half of the surface of the ice sheet melts during the summer. But from July 8 to July 12, the ice melt expanded from 40 percent of the ice sheet to 97 percent, according to scientists who analyzed the data from satellites deployed by NASA and India’s space research institute.

“I started looking at the satellite imagery and saw something that was really unprecedented” since the advent of satellite imaging of the earth’s frozen surface, or cryosphere, said Thomas L. Mote, a climate scientist at the University of Georgia who for 20 years has been studying ice changes on Greenland detected by satellite.

While scientists described it as an “extreme event” not previously recorded from space, they hastened to add that it was normal in a broader historical context.

Ice core samples taken from the summit of Greenland’s ice sheet that shed light on 10,000 years of its history show that a similar large-scale melting event has happened roughly every 150 years, said Lora Koenig, a glaciologist with NASA’s Goddard Space Flight Center who has also studied the satellite imagery. Because the previous vast melt occurred in 1889, this year’s is more or less on schedule, she said.

During the event, the surface ice on the sheet’s summit was always within a degree Celsius (1.8 degrees Fahrenheit) or so of refreezing, Dr. Koenig added. Around July 14, the ice loss began to reverse, she said.

Nonetheless, the scientists said, the melt was significant because Greenland’s ice sheet is unequivocally shrinking as a result of the warming of the world’s oceans, and the event could help broaden their insights into climate change and earth systems."

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The BBC here in England carried this story...

http://www.bbc.co.uk/news/world-europe-18978483

I've just checked their Science and Environment section and I note that they're carrying another 'polar ice' news story...Something we may be hearing a lot more of in the future.

http://www.bbc.co.uk/news/science-environment-18959399

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