A re-evaluation of the coherence between global-average atmospheric CO2 and temperatures at interannual time scales

[1] Frequency-dependent coherence between atmospheric CO2 and historical temperatures reveals climate feedbacks within Earth’s carbon cycle. Coherence between interannual fluctuations in global-average temperature and atmospheric CO2 has changed over time. Since 1979, at Mauna Loa and other observation sites, interannual coherence exhibits a 90 phase lag that suggests a direct correlation between temperatures and the time-derivative of CO2. The coherence transition can be explained if the response time of CO2 to a global temperature fluctuation has lengthened from 6 months to at least 15 months. A longer response time may reflect saturation of the oceanic carbon sink, but a transient shift in ocean circulation may play a role. Coherent annual-cycle fluctuations in CO2 and temperature are evident in the 1958–1988 time series, but not since 1979. Coherence of interannual CO2 variations with gridpoint temperature anomalies are strongest in the tropical oceans. Citation: Park, J. (2009), A re-evaluation of the coherence between global-average atmospheric CO2 and temperatures at interannual time scales, Geophys. Res. Lett., 36, L22704, doi:10.1029/2009GL040975.