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, CO 2 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. © Springer 2005.