The Arctic sea ice is disintegrating "100 years ahead of schedule", having dropped 22% this year below the previous minimum low, and it may completely disappear as early as the northern summer of 2013. This is far beyond the predictions of the International Panel on Climate Change and is an example of global warming impacts happening at lower temperature increases and more quickly than projected. What are the lessons from the Arctic summer of 2007?

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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