Indications of climate feedbacks on carbon dioxide from combined records of atmospheric CO2 and O2

Background/Question/Methods The long-term time series of atmospheric CO2 and O2 concentrations from the Scripps Institution of Oceanography now span 51 and 19 years, respectively. Together with ice-core CO2 records, these atmospheric records provide constraints on the sensitivity of the land and ocean sinks to climate changes. To extract climate signals from the records it is necessary to account for known processes influencing CO2 and O2, such as fossil-fuel burning, land use emissions, and sink processes on land and in the oceans, as represented by reservoir models consistent with additional observational constraints, such as the uptake of chlorofluorocarbons by the ocean. Results/Conclusions A comparison of the observed trends against the trends expected in the absence of climate change shows that global warming is probably reducing the efficiency of both the land and ocean CO2 sinks. The resolvable warming effects are small, however, and only marginally significant as a climate feedback. Uncertainty in land-use emissions and on sink processes on land confounds a clear analysis of trends in land fluxes. Significant feedbacks from warming effects on soils and other carbon pools with long turnover times therefore cannot be ruled out. But there is no evidence for such an effect being important to date at the global scale. The O2 trend analysis suggests that the oceans are losing O2 at a significant rate globally, consistent with an expansion of O2 minimum zones in the oceans.