Giving a hard number as a critical threshold for dangerous climate change -  temperature rise below 2 degrees Celsius - has not helped climate negotiations. 

The USA, for example, has led the developed world in reducing emissions from energy, though to be fair the anti-nuclear stance of the US led to runaway emissions from the 1980s on so things are now only getting back to even there. Yet for all the emissions the US has reduced, the rest of the world has accelerated. China is the world's top polluter but has been exempt from all negotiations because it is considered a developing nation, the same goes for India and Mexico.

It wouldn't matter anyway, says a new analysis from the University of Gothenburg and Columbia University, which postulates that negotiations based on a temperature threshold fail because its value is determined by nature and is inherently uncertain. 

So climate negotiators need different strategies. Astrid Dannenberg, post-doctoral researcher in economics at the University of Gothenburg, and international affairs professor Scott Barrett of Columbia University, speculate on the paradox of why countries would agree to a collective goal, aimed at reducing the risk of climate catastrophe, but act as if they were blind to the risk.

If the critical threshold for climate catastrophe could be identified with scientific certainty, they say that countries very likely would propose a collective target certain to avoid catastrophe, would pledge to contribute their fair share to the global effort, and would act so as to fulfill their promises.

But there is scientific uncertainty about the climate threshold, countries are very likely to do less collectively than is needed to avert catastrophe. The analytical framework of Dannenberg and Barrett concludes that the failure of negotiations is practically certain, because the climate threshold is determined by nature and so uncertainty about its value is substantially irreducible.

“Climate negotiations are more complex that the game played by the participants in our experiment. The basic incentive problem, however, is the same and our research shows that scientific uncertainty about the dangerous threshold changes behavior dramatically,” Dannenberg says.

Their research may explain why the UN climate negotiations have been framed around meeting the 2 degrees Celsius threshold and why negotiators wanted the threshold to be determined by science rather than by politics because only the former would be credible. Yet, the emission reductions countries have pledged in Copenhagen in 2009 virtually guarantee that this target will be missed.

”We will not know until 2020 if the Copenhagen Accord pledges will be met, but if our results are a reliable guide, countries may end up emitting even more than they pledged – with potentially profound and possibly irreversible consequences. Our research suggests that negotiators should focus their attention on alternative strategies for collective action, such as trade restrictions or technology standards,” Barrett says.

Citation: Scott Barrett and Astrid Dannenberg, 'Climate negotiations under scientific uncertainty', 
 PNAS October 8, 2012 doi: 10.1073/pnas.1208417109