Predicting the Long Term Future of

Atmospheric CO2

S. H. Lam

Abstract

Linear and nonlinear analyses are performed on a generic carbon cycle model, exploiting available empirical information and avoiding detailed physics as far as possible. It is shown that the ability to reproduce CO2 historical data of past decades is neither necessary nor sufficient to establish credibility for the century-timescale predictions. This is because the relevant CO2 historical data is driven by a ``rapid'' exponential forcing term, while the future forcing term of interest is expected to be flat and slowly time varying. Simple analytical formulas relating long term atmospheric CO2 level and anthropogenic emission are derived, involving only three parameters. In the century-timescale, there is no known quick way to empirically determine or validate these parameters. An estimate of the time to breach an user-specified threshold of atmospheric CO2 level in terms of this parameter is provided.

Last updated April 1, 1998.