The Likely Range of Climate Sensitivity

The IPCC suggests a “likely range” for the equilibrium climate sensitivity of atmospheric carbon dioxide. At the recommended upper limit of this likely range, the calculated temperature rise (using the quasi-steady approximation) is found to be substantially higher than the observed historical data. Theoretically, the quasi-steady response is indeed expected to be higher than the actual (time dependent) response—the difference should be proportional to a (thermal inertia) time lag parameter τ . Estimates of the value of τ—based on currently available observational data—suggest that the upper limit for equilibrium climate sensitivity is significantly smaller than that suggested by the IPCC.