Masthead graphic based on a painting by Gudrun Thriemer.

Tuesday, November 20, 2007

David Spratt, "The big melt: lessons from the Arctic summer of 2007," CarbonEquity, October 2007.

(with input from Philip Sutton, Greenleap Strategic Institute Inc.)

Note: Unless otherwise specified, temperature increases are from the 1750 _pre-industrial level. The increase was 0.7°C to 2000 and 0.8°C to 2006.

Executive summary

• Climate change impacts are happening at lower temperature increases and more quickly than projected.
• The Arctic's floating sea ice is headed towards rapid summer disintegration as early as 2013, a century ahead of the International Panel on Climate Change (IPCC) projections.
• The rapid loss of Arctic sea ice will speed up the disintegration of the Greenland ice sheet, and a rise in sea levels by even as much as 5 metres by the turn of this century is possible.
• The Antarctic ice shelf reacts far more sensitively to warming temperatures than previously believed.
• Long-term climate sensitivity (including "slow" feedbacks such as carbon cycle feedbacks which are starting to operate) may be double the IPCC standard.
• A doubling of climate sensitivity would mean we passed the widely accepted 2°C threshold of "dangerous anthropogenic interference" with the climate four decades ago, and would require us to find the means to engineer a rapid drawdown of current atmospheric greenhouse gas.
• Carbon dioxide (CO2) emissions are now growing more rapidly than "business-as-usual", the most pessimistic of the IPCC scenarios.
• Temperatures are now within ≈1°C of the maximum temperature of the past million years.
• We must choose targets and take actions that can actually solve the problem in a timely manner.
• The object of policy-relevant advice must be to avoid unacceptable outcomes and seemingly extreme or alarming possibilities, not to determine just the apparently most likely outcome.
• The 2°C warming cap is a political compromise; with the speed of change now in the climate system and the positive feedbacks that 2°C will trigger, it looms for perhaps billions of people and millions of species as a death sentence.
• To allow the reestablishment and long-term security of the Arctic summer sea ice it is likely to be necessary to bring global warming back to a level at or below 0.5°C (a long-term precautionary warming cap) and for the level of atmospheric greenhouse gases at equilibrium to be brought down to or below a long-term precautionary cap of 320 ppm CO2e.
• The IPCC suffers from a scientific reticence and in many key areas the IPCC process has been so deficient as to be an unreliable and dangerously misleading basis for policy-making.

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