Are Uncertainties in Climate and Energy Systems a Justification for Stronger Near-term Mitigation Policies? Prepared for the Pew Center on Global Climate Change

Defining long-run stabilization targets for atmospheric CO2 is ultimately a political question since it depends on value judgments. However, because of the enormous uncertainties that surround projections of climate change, their impacts and mitigation costs, any proposed stabilization target is, quite expectedly, controversial. This uncertainty, some have argued, implies that climatic change might be of minor consequence; but, comparably likely, as others have suggested, climate change could as well have potentially catastrophic implications. Thus, since the climate science, impacts and policy analytic communities cannot rule out with high confidence the possibility of a variety of serious or even catastrophic outcomes, we argue that it is wise to keep many options open. Such flexibility also includes retaining low stabilization targets on the bargaining table for climate policy options. We show how uncertainties could demonstrate that near-term abatement can be both cost-efficient and necessary to reduce the risk of “dangerous” climate change. The cost of meeting low-stabilization targets are assessed in the context of conventional economic models and found to imply only a minor impact on the expected overall economic growth rates over the next century— achieving stringent targets like 450 ppm could represent only a few year’s lost GDP growth rate in 2100 as compared to an order of magnitude economic expansion in the baseline case. Such “low cost climate insurance” might be politically quite acceptable once these relatively minor delay times were more widely known.