Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 5 6 2008 10.5194/bg-5-1601-2008 http://www.biogeosciences.net/5/1601/2008/ http://www.biogeosciences.net/5/1601/2008/bg-5-1601-2008.html http://www.biogeosciences.net/5/1601/2008/bg-5-1601-2008.pdf 1601 1613 2008-11-28 Anthropogenic and biophysical contributions to increasing atmospheric CO₂ growth rate and airborne fraction M. R. Raupach michael.raupach@csiro.au J. G. Canadell C. Le Quéré Global Carbon Project, CSIRO Marine and Atmospheric Research, Canberra, Australia School of Environmental Sciences, University of East Anglia, Norwich, UK British Antarctic Survey, Cambridge, UK We quantify the relative roles of natural and anthropogenic influences on the growth rate of atmospheric CO₂ and the CO₂ airborne fraction, considering both interdecadal trends and interannual variability. A combined ENSO-Volcanic Index (EVI) relates most (~75%) of the interannual variability in CO₂ growth rate to the El-Niño-Southern-Oscillation (ENSO) climate mode and volcanic activity. Analysis of several CO₂ data sets with removal of the EVI-correlated component confirms a previous finding of a detectable increasing trend in CO₂ airborne fraction (defined using total anthropogenic emissions including fossil fuels and land use change) over the period 1959–2006, at a proportional growth rate 0.24% y^−1 with probability ~0.9 of a positive trend. This implies that the atmospheric CO₂ growth rate increased slightly faster than total anthropogenic CO₂ emissions. To assess the combined roles of the biophysical and anthropogenic drivers of atmospheric CO₂ growth, the increase in the CO₂ growth rate (1.9% y^−1 over 1959–2006) is expressed as the sum of the growth rates of four global driving factors: population (contributing +1.7% y^−1); per capita income (+1.8% y^−1); the total carbon intensity of the global economy (−1.7% y^−1); and airborne fraction (averaging +0.2% y^−1 with strong interannual variability). The first three of these factors, the anthropogenic drivers, have therefore dominated the last, biophysical driver as contributors to accelerating CO₂ growth. Together, the recent (post-2000) increase in growth of per capita income and decline in the negative growth (improvement) in the carbon intensity of the economy will drive a significant further acceleration in the CO₂ growth rate over coming decades, unless these recent trends reverse. Achard, F., Eva, H. D., Mayaux, P., Stibig, H. J., and Belward, A.: Improved estimates of net carbon emissions from land cover change in the tropics for the 1990s, Global Biogeochem. Cy., 18, GB2008.1–GB2008.11, doi:10.1029/2003GB002142, 2004. Ammann, C. M., Meehl, G. A., Washington, W. M., and Zender, C. S.: A monthly and latitudinally varying volcanic forcing dataset in simulations of 20th century climate, Geophys. Res. Lett., 30, 1657, doi:10.1029/2003GL016875, 2003. Box, G., Jenkins, G. M., and Reinsel, G.: Time series analysis: forecasting and control, 3rd edition, Prentice Hall, Englewood Cliffs, NJ, USA, 592 pp., 1994. Canadell, J. G., Le Quéré, C., Raupach, M. R., Field, C. B., Buitenhuis, E. T., Ciais, P., Conway, T. J., Gillett, N. P., Houghton, R. A., and Marland, G.: Contributions to accelerating atmospheric CO₂ growth from economic activity, carbon intensity, and efficiency of natural sinks, PNAS, 0702737104, 104, 18 866–18 870, 2007. DeFries, R. S., Houghton, R. A., Hansen, M. C., Field, C. B., Skole, D., and Townshend, J.: Carbon emissions from tropical deforestation and regrowth based on satellite observations for the 1980s and 1990s, PNAS, 99, 14 256–14 261, 2002. Enting, I. G.: Laplace transform analysis of the carbon cycle, Environ. Model. Software, 22, 1488–1497, 2007. Friedlingstein, P., Cox, P., Betts, R., Bopp, L., von Bloh, W., Brovkin, V., Cadule, P., Doney, S., Eby, M., Fung, I., Bala, G., John, J., Jones, C., Joos, F., Kato, T., Kawamiya, M., Knorr, W., Lindsay, K., Matthews, H. D., Raddatz, T., Rayner, P., Reick, C., Roeckner, E., Schnitzler, K. G., Schnur, R., Strassmann, K., Weaver, A. J., Yoshikawa, C., and Zeng, N.: Climate-carbon cycle feedback analysis: Results from the C4MIP model intercomparison, J. Clim., 19, 3337–3353, 2006. Grainger, A.: Difficulties in tracking the long-term global trend in tropical forest area, PNAS, 105, 818–823, 2008. Gruber, N., Friedlingstein, P., Field, C. B., Valentini, R., Heimann, M., Richey, J. D., Romero Lankao, P., Schulze, E.-D., and Chen, C.-T. A.: The vulnerability of the carbon cycle in the 21st century: an assessment of carbon-climate-human interactions, in: The Global Carbon Cycle: integrating humans, climate, and the natural world, edited by: Field, C. B. and Raupach, M. R., Island Press, Washington, USA, 45–76, 2004. Gu, L. H., Baldocchi, D. D., Wofsy, S. C., Munger, J. W., Michalsky, J. J., Urbanski, S. P., and Boden, T. A.: Response of a deciduous forest to the Mount Pinatubo eruption: enhanced photosynthesis, Science, 299, 2035–2038, 2003. Hansen, M. C., Stehman, S. V., Potapov, P. V., Loveland, T. R., Townshend, J. R. G., DeFries, R. S., Pittman, K. W., Arunarwati, B., Stolle, F., Steininger, M. K., Carroll, M., and DiMiceli, C.: Humid tropical forest clearing from 2000 to 2005 quantified by using multitemporal and multiresolution remotely sensed data, PNAS, 105, 9439–9444, 2008. Houghton, R. A.: Revised estimates of the annual net flux of carbon to the atmosphere from changes in land use and land management 1850–2000, Tellus, 55B, 378–390, 2003. Houghton, R. A.: Aboveground forest biomass and the global carbon balance, Global Change Biol., 11, 945–958, 2005. Jones, C. D., Collins, M., Cox, P. M., and Spall, S. A.: The carbon cycle response to ENSO: a coupled climate-carbon cycle model study, J. Clim., 14, 4113–4129, 2001. Jones, C. D. and Cox, P. M.: Modeling the volcanic signal in the atmospheric CO₂ record, Global Biogeochem. Cy., 15, 453-465, 2001. Jones, C. D. and Cox, P. M.: On the significance of atmospheric CO₂ growth rate anomalies in 2002–2003, Geophys. Res. Lett., 32, L14816, doi:10.1029/2005GL023027, 2005. Keeling, C. D. and Revelle, R.: Effects of El-Niño southern oscillation on the atmospheric content of carbon-dioxide, Meteoritics, 20, 437–450, 1985. Keeling, C. D., Whorf, T. P., Wahlen, M., and Vanderplicht, J.: Interannual extremes in the rate of rise of atmospheric carbon-dioxide since 1980, Nature, 375, 666–670, 1995. Keeling, C. D., Piper, S. C., Bacastow, R. B., Wahlen, M., Whorf, T. P., Heimann, M., and Meijer, H. A.: Exchanges of atmospheric CO₂ and $^13$CO₂ with the terrestrial biosphere and oceans from 1978 to 2000: 1. global aspects, SIO Reference Series, 01-06, Scripps Institution of Oceanography, San Diego, USA, 88, 2001. Keeling, C. D., Piper, S. C., Bacastow, R. B., Wahlen, M., Whorf, T. P., Heimann, M., and Meijer, H. A.: Atmospheric CO₂ and $^13$CO₂ exchange with the terrestrial biosphere and oceans from 1978 to 2000: observations and carbon cycle implications, in: A history of atmospheric CO₂ and its effects on plants, animals, and ecosystems, edited by: Ehleringer, J. R., Cerling, T. E., and Dearing, M. D., Springer Verlag, New York, USA, 83–113, 2005. Knorr, W., Scholze, M., Gobron, N., Pinty, B., and Kaminski, T.: Global-scale drought caused atmospheric CO₂ increase, EOS, 86, 178–181, 2005. Le Quéré, C., Rodenbeck, C., Buitenhuis, E. T., Conway, T. J., Langenfelds, R., Gomez, A., Labuschagne, C., Ramonet, M., Nakazawa, T., Metzl, N., Gillett, N., and Heimann, M.: Saturation of the southern ocean CO₂ sink due to recent climate change, Science, 316, 1735–1738, 2007. Lutz, W., Sanderson, W., and Scherbov, S.: The end of world population growth, Nature, 412, 543–545, 2001. Marland, G., Boden, T. A., and Andres, R. J.: Global, regional, and national CO₂ emissions, in: Trends: a compendium of data on global change, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, US Department of Energy, Oak Ridge, Tennessee, USA, available online: http://cdiac.ornl.gov, 2006. Marland, G. and Rotty, R. M.: Carbon dioxide emissions from fossil fuels: a procedure for estimation and results for 1950–82, Tellus B, 36, 232–261, 1984. Mishchenko, M. I., Geogdzhayev, I. V., Rossow, W. B., Cairns, B., Carlson, B. E., Lacis, A. A., Liu, L., and Travis, L. D.: Long-term satellite record reveals likely recent aerosol trend, Science, 315, 1543, 2007. Nakicenovic, N.: Socioeconomic driving forces of emissions scenarios, in: The Global Carbon Cycle: integrating humans, climate, and the natural world, edited by: Field, C. B. and Raupach, M. R., Island Press, Washington, 225–239, 2004. Nakicenovic, N., Alcamo, J., Davis, G., de Vries, B., Fenhann, J., Gaffin, S., Gregory, K., Grubler, A., Jung, T. Y., Kram, T., La Rovere, E. L., Michaelis, L., Mori, S., Morita, T., Pepper, W., Pitcher, H., Price, L., Raihi, K., Roehrl, A., Rogner, H.-H., Sankovski, A., Schlesinger, M., Shukla, P., Smith, S., Swart, R., van Rooijen, S., Victor, N., and Dadi, Z.: IPCC Special Report on Emissions Scenarios, Cambridge University Press, Cambridge, UK, and New York, USA, 599 pp., 2000. Oeschger, H., Siegenthaler, U., and Heimann, M.: The carbon cycle and its perturbations by man, in: Interactions of Energy and Climate, edited by: Bach, W., Pankrath, J., and Williams, J., Reidel, Dordrecht, The Netherlands, 107–127, 1980. Raupach, M. R., Marland, G., Ciais, P., Le Quéré, C., Canadell, J. G., Klepper, G., and Field, C. B.: Global and regional drivers of accelerating CO₂ emissions, PNAS, 0700609104, 104, 10 288–10 293, 2007. Sabine, C. L., Heimann, M., Artaxo, P., Bakker, D. C. E., Chen, C.-T. A., Field, C. B., Gruber, N., Le Quéré, C., Prinn, R. G., Richey, J. D., Romero Lankao, P., Sathaye, J. A., and Valentini, R.: Current status and past trends of the global carbon cycle, in: The global carbon cycle: integrating humans, climate, and the natural world, edited by: Field, C. B. and Raupach, M. R., Island Press, Washington, USA, 17–44, 2004. Wolter, K. and Timlin, M. S.: Monitoring ENSO in COADS with a seasonally adjusted principal component index, in: Proceedings of the 17th Climate Diagnostics Workshop, Oklahoma Climatological Survey, Cooperative Institute for Mesoscale Meteorological Studies, and the School of Meteorology, University of Oklahoma, Norman, OK, USA, 52–57, 1993. Wolter, K. and Timlin, M. S.: Measuring the strength of ENSO – how does 1997/98 rank?, Weather, 53, 315–324, 1998. Zeng, N., Mariotti, A., and Wetzel, P.: Terrestrial mechanisms of interannual CO₂ variability, Global Biogeochem. Cy., 19, GB1016, doi:10.1029/2004GB002273, 2005.