Implications of Carbon Cycle Feedbacks for Social Cost of Carbon

Abstract:

The natural sinks of anthropogenic CO₂ are critical the earth system response to CO₂ emissions. Currently, excess CO₂ is removed from the atmosphere into the land biosphere and ocean at a rate nearly 50% that of fossil fuel emissions, which provides a significant buffer against increased climate change. However, as the climate changes, the ability of the natural CO₂ sinks to continue capturing emissions is projected to decrease, which will lead to additional warming resulting in positive feedbacks that amplify the impacts of CO₂ emissions. The potential magnitude of this positive climate feedback is uncertain. In this work, we discuss the effect of including the carbon cycle feedback in the integrated assessment model, DICE, using a simple parameterization of the global carbon cycle. We introduce uncertainty to show that optimal policy decisions can be strongly affected by the still-uncertain carbon cycle dynamics. Ignoring the feedbacks in the carbon cycle in policymaking leads to increased damages and a higher social cost of carbon. Uncertainty in the carbon feedbacks plays an important role and we show that measurements of the global carbon cycle made over several decades and measurement-types can be incorporated into policy decisions to facilitate learning and potentially averting trillions of dollars in additional damages due to climate change.