http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00751.1
If anthropogenic CO2 emissions cease, will atmospheric CO2 concentration continue to increase? Andrew H. MacDougall,* Michael Eby, and Andrew J. Weaver Journal of Climate DOI: 10.1175/JCLI-D-12-00751.1 Abstract If anthropogenic CO2 emissions were to suddenly cease, the evolution of the atmospheric CO2 concentration would depend on the magnitude and sign of natural carbon sources and sinks. Experiments using Earth system models indicate that overall carbon sinks dominate, such that upon cessation of anthropogenic emissions, atmospheric CO2 levels decrease over time. However, these models have typically neglected the permafrost carbon pool, which has the potential to introduce an additional terrestrial source of carbon to the atmosphere. Here we use the University of Victoria Earth System Climate Model (UVic ESCM), which has recently been expanded to include permafrost carbon stocks and exchanges with the atmosphere. In a scenario of zeroed CO2 and sulphate aerosol emissions, we assess whether the warming induced by specified constant concentrations of non-CO2 greenhouse gases could slow the CO2 decline following zero emissions, or even reverse this trend and cause CO2 to increase over time. We find that a radiative forcing from non-CO2 gases of approximately 0.6 W m-2 results in a near balance of CO2 emissions from the terrestrial biosphere and uptake of CO2 by the oceans, resulting in near-constant atmospheric CO2 concentrations for at least a century after emissions are eliminated. At higher values of non-CO2 radiative forcing, CO2 concentrations increase over time, regardless of when emissions cease during the 21st century. Given that the present-day radiative forcing from non-CO2 greenhouse gases is about 0.95 W m-2, our results suggest that if we were to eliminate all CO2and aerosols emissions without also decreasing non-CO2greenhouse gas emissions, CO2 levels would increase over time, resulting in a small increase in climate warming associated with this positive permafrost carbon feedback. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/groups/opt_out.
