Toward a Common Framework

Some of the greatest challenges in managing the carbon-climate-human system for a sustainable future involve establishing appropriate criteria for comparing options. Ultimately, we need a framework where any option can be explored in terms of its implications for the climate system, its implications for energy, and its other impacts on ecosystems and humans (Raupach et al., Chapter 6). Many of the challenges involve processes that operate on different timescales. The sensitivity to time frame of the relative value of mitigating CO2 and CH4 emissions illustrates the problem. On a timescale of a few years, decreasing CH4 emissions has a large impact on climate, but this impact decreases over decades as a consequence of the relatively short atmospheric life of CH4 (Manne and Richels, Chapter 25). Carbon management through reforestation and afforestation potentially yields benefits over many decades, but these benefits disappear or reverse when forests stop growing, are harvested, or are disturbed. A decision about using a plot for a forest plantation versus a photovoltaic array needs to be based on a common framework for assessing the options, a framework that includes not only time frames, but also ancillary costs and benefits (Edmonds, Chapter 23).

All of the decisions that underlie the transition to a sustainable energy future require placing the decision in a larger context (Raupach et al., Chapter 6). Institutions, culture, economic resources, and perspectives on intergenerational equity all shape opportunities for and constraints on managing the carbon cycle.

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