E7 : Climate decision-making under uncertainty

698

Many climate scientists and economists have studied the probable build-up of GhG concentrations and resulting increases in global temperatures if no steps are taken to reduce emissions. Although there is considerable uncertainty over the economic impact of higher temperatures, the consensus view is that the impact could be significant, so that there would be a future benefit from reducing emissions today. The cost of reducing emissions (or preventing them from growing above current levels) can be assessed as well, although here too there is uncertainty over the specific numbers.

425

Even further, climate change raises important questions about […] how to devise policies in the presence of uncertainty.

427

Climate scientists have developed complex models to predict how much average temperatures will increase as CO2 concentrations increase. Because predicting long-term climate trends involves considerable uncertainty, these models have produced a range of potential outcomes. Adding to the uncertainty in models is the extent to which warming will be influenced by the policy decisions made in the next couple of decades.

164

First, there are disagreements about how rapidly global warming is likely to occur and what the economic cost will be.

173

Scientists disagree about how much carbon emissions are contributing to climate change and what the damage from climate change will be. In addition, the cost of reducing carbon emissions depends on the method of reduction used. As a result, neither the marginal benefit curve nor the marginal cost curve for reducing carbon emissions is known with certainty. This uncertainty makes it difficult for policymakers to determine the economically efficient level of carbon emissions and is the source of much of the current debate. In any case, economists agree that the total cost of completely eliminating carbon emissions is much greater than the total benefit.

300

Par ailleurs, ils font remarquer que les coûts liés à la pollution et les impacts du changement climatique sont sans cesse réévalués à la hausse, avec la mise en avant de risques majeurs (effets de seuil, irréversibilités, etc.). Dans ce cas, on sort du domaine du risque quantifiable pour entrer dans celui de l'incertitude radicale. Si tel est le cas, l'application stricte du principe de précaution doit se substituer à l'analyse coût-bénéfice traditionnelle.