Adaptation and the guardrail approach to tolerable climate change

Windows delineating tolerable or "acceptable" conditions associated with cl imate change can be defined in terms of a variety of parameters; a prelimin ary window offered by the Scientific Advisory Council on Global Change of t he Federal Government of Germany sets limits on temperature change and the rate of temperature change. Investment in adaptation can alter the size and shape of these windows, and different emissions trajectories are associate d with different limiting points on their boundaries. As a result, the valu e of adaptation depends upon both the underlying structure of the tolerable window and the basecase emissions trajectory. Given uncertainty about both , the best near-term policy should be cast in a sequential decision-making framework. Seen in this light, improved adaptive potential can either reduc e the cost of sustaining tolerable climate change or increase the opportuni ty cost of holding to more restrictive boundaries.