Introduction
The UN Framework Convention on Climate Change (UNFCCC) shifted the attention of the policy community from stabilizing greenhouse gas emissions to stabilizing atmospheric greenhouse gas concentrations. While this represents a step forward, it does not go far enough. We find that, given the uncertainty in the climate system, focusing on atmospheric concentrations is likely to convey a false sense of precision. The causal chain between human activity and impacts is laden with uncertainty. From a benefit–cost perspective, it would be desirable to minimize the sum of mitigation costs and damages. Unfortunately, our ability to quantify and value impacts is limited. For the time being, we must rely on a surrogate. Focusing on temperature rather than on concentrations provides much more information on what constitutes an ample margin of safety. Concentrations mask too many uncertainties that are crucial for policymaking.
The climate debate is fraught with uncertainty. In order to better understand the link between human activities and impacts, we must first understand the causal chain between the two, i.e., the relationship between human activities, emissions, concentrations, radiative forcing, temperature, climate, and impacts. The focus of the UNFCCC is on atmospheric concentrations of greenhouse gases. Although this represents a major step forward by advancing the debate beyond emissions, it does not go far enough. In this paper, we carry the analysis beyond atmospheric concentrations to temperature change.