Emissions and Atmospheric CO2 Stabilization: Long-Term Limits and Paths

The objective of stabilization of greenhouse gas concentrations is often envisioned as a monotonic approach to higher constant concentrations. For CO₂ to approach a constant concentration over a finite time, CO₂ emissions must peak and then gradually approach zero over 1,000+ years, regardless of the concentration level. While this intellectual architecture has proved useful, we suggest consideration of a broader range of scenarios, including ones in which net emissions decline to zero over a finite period of time resulting in a maximum CO₂ concentration followed by a long-term decline to a lower level. Carbon cycle model results illustrate these scenarios.