Contributing Authors D. Archer, M.R. Ashmore, O. Aumont, D. Baker, M. Battle, M. Bender, L.P. Bopp, P. Bousquet, K. Caldeira, P. Ciais, P.M. Cox, W. Cramer, F. Dentener, I.G. Enting, C.B. Field, P. Friedlingstein, E.A. Holland, R.A. Houghton, J.I. House, A. Ishida, A.K. Jain, I.A. Janssens, F. Joos, T. Kaminski, C.D. Keeling, R.F. Keeling, D.W. Kicklighter, K.E. Kohfeld, W. Knorr, R. Law, T. Lenton, K. Lindsay, E. Maier-Reimer, A.C. Manning, R.J. Matear, A.D. McGuire, J.M. Melillo, R. Meyer, M. Mund, J.C. Orr, S. Piper, K. Plattner, P.J. Rayner, S. Sitch, R. Slater, S. Taguchi, P.P. Tans, H.Q. Tian, M.F. Weirig, T. Whorf, A. Yool

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The Carbon Cycle and Atmospheric Carbon Dioxide

[1] High-precision, multispecies measurements of flask air samples since 1992 from CSIRO's global sampling network reveal strong correlation among interannual growth rate variations of CO2 and its δ13C, H2, CH4, and CO. We show that a major fraction of the variability is consistent with two emission pulses coinciding with large biomass burning events in 1994/1995 and 1997/1998 in tropical and boreal regions, and observations of unusually high levels of combustion products in the overlying troposphere at these times. Implied pulse strengths and multispecies emission ratios are not consistent with any other single process, but do not exclude possible contributions from covarying processes that are linked through climatic forcing. Comparison of CO2 with its δ13C indicates that most of the CO2 variation is from terrestrial exchange, but does not distinguish forcing by biomass burning from imbalance in photosynthesis/respiration of terrestrial ecosystems. Partitioning of terrestrial CO2 fluxes is constrained by H2, CH4, and CO, all of which are products of biomass burning but which have no direct link to net respiration of CO2. While CO is a strong indicator of biomass burning, its short lifetime prevents it from usefully constraining the magnitude of CO2 emissions. If the H2 and CH4 variations were dominated by biomass burning, they would imply associated carbon emissions in excess of mean annual levels of other years, of 0.6–3.5 and 0.8–3.7 Pg C for 1994/1995 and 1997/1998, respectively. The large range in emission estimates mainly reflects uncertainty in H2/CO2 and CH4/CO2 emission ratios of fires in these years.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001GB001466

Interannual growth rate variations of atmospheric CO2 and its δ13C, H2, CH4, and CO between 1992 and 1999 linked to biomass burning

Oceans general circulation models predict that global warming may cause a decrease in the oceanic O2 inventory and an associated O2 outgassing. An independent argument is presented here in support of this prediction based on observational evidence of the ocean's biogeochemical response to natural warming. On time scales from seasonal to centennial, natural O2 flux/heat flux ratios are shown to occur in a range of 2 to 10 nmol O2 per Joule of warming, with larger ratios typically occurring at higher latitudes and over longer time scales. The ratios are several times larger than would be expected solely from the effect of heating on the O2 solubility, indicating that most of the O2 exchange is biologically mediated through links between heating and stratification. The change in oceanic O2 inventory through the 1990's is estimated to be 0.3 - 0.4 x 10(exp 14) mol O2 per year based on scaling the observed anomalous long-term ocean warming by natural O2 flux/heating ratios and allowing for uncertainty due to decadal variability. Implications are discussed for carbon budgets based on observed changes in atmospheric O2/N2 ratio and based on observed changes in ocean dissolved inorganic carbon.

https://www.pnas.org/content/pnas/99/12/7848.full.pdf

The change in oceanic O2 inventory associated with recent global warming

Measurements of atmospheric O2/N2 ratio and CO2 concentration are presented over the period 1989‐2003 from the Scripps Institution of Oceanography global flask sampling network A formal framework is described for making optimal use of these data to estimate global oceanic and land biotic carbon sinks For the 10-yr period from 1990 to 2000, the oceanic and land biotic sinks are estimated to be 19 ± 06 and 12 ± 08 Pg C yr −1 , respectively, while for the 10-yr period from 1993 to 2003, the sinks are estimated to be 22 ± 06 and 05 ± 07 Pg C yr−1, respectively These estimates, which are also compared with earlier results, make allowance for oceanic O2 and N2 outgassing based on observed changes in ocean heat content and estimates of the relative outgassing per unit warming For example, for the 1993‐2003 period we estimate outgassing of 045 × 10 14 mol O2 yr −1 and 020 × 10 14 mol N2 yr −1 , which results in a correction of 05 Pg C yr −1 on the oceanic and land biotic carbon sinks The basis for this oceanic outgassing correction is reviewed in the context of recent model estimates The main contributions to the uncertainty in the global sinks averages are from the estimates for oceanic outgassing and the estimates for fossil fuel combustion The oceanic sink of 22 Pg C yr −1 for 1993‐2003 is consistent, within the uncertainties, with the integrated accumulation of anthropogenic CO2 in the ocean since 1800 as recently estimated from oceanic observations, assuming the oceanic sink varied over time as predicted by a box-diffusion model

http://bluemoon.ucsd.edu/publications/manning/ManningandKeeling2006.pdf

Global oceanic and land biotic carbon sinks from the Scripps atmospheric oxygen flask sampling network

There is scope for land-use changes to increase or decrease CO2 concentrations in the atmosphere over the next century. Here we make simple but robust calculations of the maximum impact of such changes. Historical land-use changes (mostly deforestation) and fossil fuel emissions have caused an increase in atmospheric concentration of CO2 of 90 ppm between the pre-industrial era and year 2000. The projected range of CO2 concentrations in 2100, under a range of emissions scenarios developed for the IPCC, is 170-600 ppm above 2000 levels. This range is mostly due to different assumptions regarding fossil fuel emissions. If all of the carbon so far released by land-use changes could be restored to the terrestrial biosphere, atmospheric CO2 concentration at the end of the century would be about 40-70 ppm less than it would be if no such intervention had occurred. Conversely, complete global deforestation over the same time frame would increase atmospheric concentrations by about 130-290 ppm. These are extreme assumptions; the maximum feasible reforestation and afforestation activities over the next 50 years would result in a reduction in CO2 concentration of about 15-30 ppm by the end of the century. Thus the time course of fossil fuel emissions will be the major factor in determining atmospheric CO2 concentrations for the foreseeable future.

Andrew C. Manning

Papers

Temporal variability of atmospheric oxygen from both continuous measurements and a flask sampling network: Tools for studying the global carbon cycle