Chapter Fourteen - Mitigation

Summary

“Make me chaste and celibate—but not yet!”

—Fourth-century philosopher Saint Augustine

Climate change mitigation refers to efforts to control the concentration of atmospheric CO₂ and other greenhouse gases by reducing or preventing emission of greenhouse gases and enhancing sinks of carbon. By contrast with adaptation, which manages the local impacts of a hazard, mitigation seeks to prevent the hazard from occurring.

Carbon Mitigation and Management

“Shutting down investment in fossil fuels before you have a plan to replace their role in the energy system is neither resilient nor just.” (Energy finance expert Michael Liebreich)

Carbon management is targeted at limiting the atmospheric concentration of CO₂ and additional compounds that comprise carbon-based air pollution (e.g., methane and soot). Several comprehensive schemes have been formulated for atmospheric CO₂ emissions and carbon-based air pollution, including the IPCC AR6 WGIII Report,4 Climate Stabilization Wedges, and Project Drawdown. While the emphasis has been on atmospheric CO₂, management of other carbon pollutants is important in efforts to reduce warming. These mitigation schemes focus primarily on the sources of emissions: energy systems, transportation, industry, agriculture and forests, buildings, and urban systems.

Reducing CO₂ emissions has become an end in itself, with the implicit assumption that reducing CO₂ emissions will rapidly decrease atmospheric CO₂ and improve the climate. However, rigorous detection and attribution of the climate impacts of even very strong emission mitigation efforts will be very challenging. Emergence of a climate mitigation signal beyond natural variability can never be proven, as we would be comparing it to an unknown, counterfactual world. The challenge is to understand how atmospheric carbon will evolve in response to emissions reductions, and how the fast and slow components of the climate system will respond.

Global Carbon Cycle, Feedbacks and Budget

“There is room for words on subjects other than last words.” (Philosopher Robert Nozick, author of Anarchy, State, and Utopia)

Reservoirs of carbon in the earth system include the atmosphere, land ecosystems, the ocean, sediments, and the Earth's interior. Excluding rocks, by far the largest reservoir of carbon is the ocean. Exchanges of carbon between reservoirs occurs via various chemical, physical, geological, and biological processes. These exchanges establish a dynamical equilibrium over time in the absence of large external perturbations to the system. Since the advent of agriculture, humans have gradually influenced the carbon cycle by modifying the vegetation in land ecosystems.