A decade of subsequent research added scientific support to the notion that 2C was a dangerous threshold. Experts realized, for example, that at some increase in global temperature, the immense Greenland ice sheet would begin an unstoppable melt, raising the sea by as much as 23 feet over an unknown period. Their early calculations suggested that calamity would be unlikely as long as global warming did not exceed about 1.9 degrees Celsius.

“Risking a loss of the whole Greenland ice sheet was considered a no-go area,” said Stefan Rahmstorf, head of earth system analysis at the Potsdam Institute for Climate Impact Research in Germany. “We are talking about really sinking a lot of coastal cities.”

As the economic and scientific arguments accumulated, the Germans managed to persuade other countries to adopt the 2C target, turning it into official European policy. The proposal was always controversial, with African countries and island states, in particular, arguing that it was too much warming and would condemn them to ruin. The island states cited the potential for a large rise of the sea, and African countries feared severe effects on food production, among other problems.

But as a practical matter, the 2C target seemed the most ambitious possible, since it would require virtually ending fossil fuel emissions within 30 to 40 years. At Cancun in 2010, climate delegates made 2C one of the organizing principles of negotiations.

The talks culminating in Paris next year are seen as perhaps the best chance ever to turn that pledge into meaningful emissions limits, in part because President Obama has gone far beyond his predecessors in committing the United States, the largest historical producer of greenhouse gases, to action. That, in turn, has lured China, the largest current producer, into making its first serious commitments.

David Fuller's view

This challenge will be address more effectively if calm and objective research is produced, and sensible strategies are followed.  The solution, we already know, is not more of this century’s foolish closing of viable nuclear power stations and the building of ever more windmills, which too often have needed to be backed by an increase in coal power stations, as we have seen in Germany.  The financial cost of this blunder and the increased CO2 emissions it has produced has not persuaded emerging nations to follow Europe’s policies. 

Technology offers the solutions we require.  These range from natural gas which is by far the least polluting fossil fuel, to new nuclear power stations, and solar which is the most flexible and viable renewable power source that we currently have.  Technology even has the potential to make nuclear fission viable within the 30 to 40 years required.