Sunday, December 18, 2011

Climate sensitivity - Paleoclimate Record Points Towards Potential Rapid Climate Change by Takver

"The paleoclimate record reveals a more sensitive climate than thought, even as of a few years ago. Limiting human-caused warming to 2 degrees is not sufficient," said NASA climatologist James Hansen at the American Geophysical Society meeting on December 6 2011, "It would be a prescription for disaster."

In a press conference at the American Geophysical Union Fall meeting 2011 in San Fransisco climate scientists James Hansen, Ken Caldeira and Eelco Rohling explained that the climate sensitivity may be greater than previously thought. This has implications particularly for action on climate change mitigation and adaptation with major impacts on sea level rise, ocean acidification and many other areas. The latest proposals and pledges from Durban put the world on the path of 4.3°C of warming by the end of the century.

Detailed examination of the paleoclimate record indicates that for every degree Celsius of global temperature rise will ultimately equate to 20 meters of sea level rise. However, that sea level increase due to ice sheet loss would be expected to occur over centuries, and large uncertainties remain in predicting how that ice loss would unfold.

James Hansen on Paleoclimate record and climate sensitivity

James Hansen indicated that disintegration of ice sheets is a non-linear process that is already being seen in Greenland, and the Pine Island Glacier in West Antarctica, where the rate of ice mass loss has continued accelerating over the past decade. Indications from measurements collected from the GRACE satellites indicates that the rate of ice sheet mass loss in Greenland and West Antarctica doubles every ten years. Although the data record trend from GRACE measurements is short which entails significant uncertainty with regard to predictions, Hansen argues the continued rate of ice loss has the potential to cause multiple meters of sea level rise by 2100.

According to ice and sediment cores, we are approaching temperatures in polar regions similar to epochs when sea level was tens of metres higher. "We don't have a substantial cushion between today's climate and dangerous warming," Hansen said. "Earth is poised to experience strong amplifying feedbacks in response to moderate additional global warming."

The difference between climate change in past epochs and today is the rapid rate of change. Where in the past atmospheric CO2 content would change over thousands of years in a slow process allowing the biosphere and ecosystems to adjust, we have changed the rate of warmer at a significantly faster rate. "Humans have overwhelmed the natural, slow changes that occur on geologic timescales," Hansen said.

Hansen has been emphasising the importance of a moratorium on new coal fired power stations and phasing out dirty coal use. The IEA has estimated recently that existing and proposed power stations lock in 80 per cent of the total energy-related CO2 emissions permitted to 2035 in the 450ppm Scenario.
"We cannot burn all the fossil fuels." said Hansen at the AGU press conference, "If we burnt all of the fossil fuels we would send the planet back to the ice free state. We can't say how long it would take to get there but we know that the rate of change would be accelerating rapidly, and yet the governments and fossil fuel industry assume that we can go right ahead and go after all the coal and even begin to develop these unconventional fossil fuels like tar sands and tar shale and hydro fracking. That is a message which somehow we do not seem to have communicated as well as we need to."
Hansen also emphasised the importance of improved agricultural and forestry practices to absorb more atmospheric carbon in land carbin sinks. 

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