1 / 23

Understanding Carbon Sink Efficiencies from CO2 Airborne Fraction Trends

This article explores the trends in carbon airborne fraction as a key indicator of carbon sink efficiencies, offering insights into the impacts of anthropogenic carbon flux on the atmosphere. It delves into linear models and their controls on airborne fraction, drawing conclusions based on data from 1850 to 2100. The study discusses the relationship between carbon emissions, sink efficiency, and atmospheric carbon pools, presenting a predictive equation for airborne fraction variations. While examining the constancy of airborne fraction is crucial, this research also investigates anomalies like the 2002/2003 data point. The findings suggest that there is no definitive evidence of a long-term decreasing trend in sink efficiency, challenging assumptions about climate feedback mechanisms.

whittaker-jovani
Download Presentation

Understanding Carbon Sink Efficiencies from CO2 Airborne Fraction Trends

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. What can we learn about sink efficiencies from trends in CO2 airborne fraction ? M. Gloor, J. Sarmiento, N. Gruber University of Leeds, Princeton University, ETH Switzerland Article: ACP Discussions, 2010

  2. Outline • Introduction • Time course of anthropogenic C flux • Controls on Airborne fraction according • to linear models • Conclusions

  3. 1850 2000 2100 Cox et al. 2000 Rainforest Savannah

  4. How much anthropogenic carbon stays in the atmosphere ? => Airborne fraction (C.D. Keeling, 1973) ( ) Canadell et al. 2007, PNAS

  5. Recent statements from high-profile publications • Positive trend in AFFF+LU <=> decreasing trend of carbon ‘sink efficiency’ <=> positive carbon cycle - climate feedback • Canadell et al. PNAS, 2007, Raupach et al. 2008, LeQuere et al. • Nature Biogeoscience, 2009 • B. Constancy of AF fundamental property of system • Knorr Geophys Res. Lett. 2009 • Globally Carbon emissions accelerating Raupach et al. 2007

  6. Anthropogenic forcing

  7. Fossil Fuel Emissions (PgC yr-1) (Marland et al. 2006, updated) Fossil fuel e-folding time-scale (yr) Land use change Emissions (PgC yr-1) (Houghton et al. 2007) Year (AD)

  8. Airborne fraction predictions

  9. ‘Sink efficiency’ and linear models of the carbon cycle Here: cause = anthropogenic C flux to atmosphere effect = flux out of atmosphere to ocean and land carbon pools ‘Constant sink efficiency’ <=> with ; toc-1,tld-1‘sink efficiencies’ , atmosphere-ocean /-land C fluxes anthropogenic perturbation of atmospheric carbon

  10. Most simple linear model with ‘s’ stands for system Solution with G(t,t’) ‘Greens function’ model easily generalizable to multi-pool linear carbon cycle models by using multi-pool Greens function results very similar to the ones presented here

  11. Airborne fraction for simple cases (i) Flux to atmosphere , subscript stands for forcing, then and thus (ii) (iii)

  12. tf/ts=20/45=0.44 tf/ts=40/45=0.88 Airborne fraction (-) tf/ts=20/4.5=4.44

  13. =>Near constancy of AF reflects approximate exponential fossil fuel emissions’ rise, i.e. not fundamental system property (Bacastow and Keeling 1979) • Association between positive trend in AF and decrease in carbon sink efficiency does not hold • Need to remove variations in AF due to spin-up time effect and deviations from exponential function of anthropogenic emissions from AF if one wants to de- tect potential trends in sink efficiency from observed AF • Need an evolution equation for AF given anthropo- genic fluxes

  14. AF time evolution for actual anthropogenic fluxes to the atmosphere From the general solution for our simple model we can derive a differential equation for AF • Relative growth rate of anthropogenic emissions and relative changes in system response time-scale ts control variations in AF • Permits to predict AF variations by time-stepping equation using estimates of fossil fuel emissions and land use change

  15. Fossil fuel Emission’s Relative Growth Rate from least squares minimization

  16. Focus 1959 to present • Strong observed inter-annual variation missing in predicted AF • (as these due to non-anthropogenic forcings - e.g. volcanoes) • Residuals exhibit a trend - evidence for sink efficiency decrease ?

  17. Least squares estimation of flux corrections such that predicted and observed AF match and analyse them • One event (2002/2003) we cannot currently attribute to either external forcing or omissions in land use change fluxes • Trend in residuals disappears

  18. Signal to noise Airborne Fraction (-)

  19. Conclusions • Approximate constancy of AF due to approximate exponential increase of fossil fuel emissions • No association between positive trend in AF and negative trend in sink efficiency • May account for spin-up time and exponential growth rate deviations using predictive equation for AF • => no evidence for long-term decreasing trend in sink efficiency - potential exception: 2002/3 event • trends in AF not very good diagnostic because complicated signal and S/R quite small

  20. Canadell et al. PNAS, 2007, Raupach et al. 2008, LeQuere et al. Nature Biogeoscience, 2009 Knorr, Geophys. Res. Lett. , 2009

  21. Raupach et al. 2007 PNAS what about ‘peak oil’ ?

More Related