Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 1 2009 10.5194/acpd-9-2559-2009 http://www.atmos-chem-phys-discuss.net/9/2559/2009/ http://www.atmos-chem-phys-discuss.net/9/2559/2009/acpd-9-2559-2009.html http://www.atmos-chem-phys-discuss.net/9/2559/2009/acpd-9-2559-2009.pdf 2559 2608 2009-01-28 The radiative forcing potential of different climate geoengineering options T. M. Lenton t.lenton@uea.ac.uk N. E. Vaughan School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK Tyndall Centre for Climate Change Research, UK Climate geoengineering proposals seek to rectify the Earth's current radiative imbalance, either by reducing the absorption of incoming solar (shortwave) radiation, or by removing CO₂ from the atmosphere and transferring it to long-lived reservoirs, thus increasing outgoing longwave radiation. A fundamental criterion for evaluating geoengineering options is their climate cooling effectiveness, which we quantify here in terms of radiative forcing potential. We use a simple analytical approach, based on the global energy balance and pulse response functions for the decay of CO₂ perturbations. This aids transparency compared to calculations with complex numerical models, but is not intended to be definitive. Already it reveals some significant errors in existing calculations, and it allows us to compare the relative effectiveness of a range of proposals. By 2050, only stratospheric aerosol injections or sunshades in space have the potential to cool the climate back toward its pre-industrial state, but some land carbon cycle geoengineering options are of comparable magnitude to mitigation "wedges". Strong mitigation, i.e. large reductions in CO₂ emissions, combined with global-scale air capture and storage, afforestation, and bio-char production, i.e. enhanced CO₂ sinks, might be able to bring CO₂ back to its pre-industrial level by 2100, thus removing the need for other geoengineering. Alternatively, strong mitigation stabilising CO₂ at 500 ppm, combined with geoengineered increases in the albedo of marine stratiform clouds, grasslands, croplands and human settlements might achieve a patchy cancellation of radiative forcing. Ocean fertilisation options are only worthwhile if sustained on a millennial timescale and phosphorus addition probably has greater long-term potential than iron or nitrogen fertilisation. Enhancing ocean upwelling or downwelling have trivial effects on any meaningful timescale. Our approach provides a common framework for the evaluation of climate geoengineering proposals, and our results should help inform the prioritisation of further research into them. Akbari, H., Menson, S., and Rosenfeld, A.: Global Cooling: Increasing world-wide urban albedos to offset CO₂, Climatic Change, doi:10.1007/s10584-008-9515-9, 2008. Anderson, L. A. and Sarmiento, J. L.: Redfield ratios of remineralization determined by nutrient data analysis, Global Biogeochem. Cy., 8, 65–80, 1994. Angel, R.: Feasibility of cooling the earth with a cloud of small spacecraft near the inner Lagrange point (l1), Proc. Natl. Acad. Sci. USA, 103, 17 184–17 189, 2006. Aumount, O. and Bopp, L.: Globalizing results from ocean in situ iron fertilization studies, Global Biogeochem. Cy., 20, GB2017, doi:10.1029/2005GB002591, 2006. Bower, K., Choularton, T., Latham, J., Sahraei, J., and Salter, S.: Computational assessment of a proposed technique for global warming mitigation via albedo enhancement of marine stratocumulus clouds, Atmos. Res., 82, 328–336, 2006. Boyd, P. W.: Ranking geo-engineering schemes, Nature Geoscience, 1, 722–724, 2008. Buesseler, K. O., Lamborg, C. H., Boyd, P. W., Lam, P. J., Trull, T. W., Bidigare, R. R., Bishop, J. K. B., Casciotti, K. L., Dehairs, F., Elskens, M., Honda, M., Karl, D. M., Siegel, D. A., Silver, M. W., Steinberg, D. K., Valdes, J., Van Mooy, B., and Wilson, S.: Revisiting Carbon Flux Through the Ocean's Twilight Zone, Science, 316, 567–570, 2007. Canadell, J. G., LeQuere, 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, Proc. Natl. Acad. Sci. USA, 104, 18 866–18 870, 2007. Charlson, R. J., Lovelock, J. E., Andreae, M. O., and Warren, S. G.: Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate, Nature, 326, 655–661, 1987. Cox, P. M., Betts, R. A., Jones, C. D., Spall, S. A., and Totterdell, I. J.: Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model, Nature, 408, 184–187, 2000. Crutzen, P. J.: Albedo enhancement by stratospheric sulphur injections: A contribution to resolve a policy dilemma?, Climatic Change, 77, 211–219, 2006. Falkowski, P. G.: Evolution of the nitrogen cycle and its influence on the biological sequestration of CO₂ in the ocean, Nature, 387, 272–275, 1997. Friedlingstein, P., Cox, P., Betts, R., Bopp, L., Bloh, W. v., Brovkin, V., Doney, S., Eby, M., Fung, I., Govindasamy, B., 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., Thompson, S., Weaver, A. J., Yoshikawa, C., and Zeng, N.: Climate-carbon cycle feedback analysis: Results from the C4MIP model intercomparison, J. Climate, 19, 3337–3353, 2006. Gaskill, A.: Summary of Meeting with US DOE to discuss Geoengineering options to prevent abrupt and long-term climate change, available at: http://www.global-warming-geo-engineering.org/DOE-Meeting/DOE-Geoengineering-Climate-Change-Meeting/ag1.html (last access: 20 January 2009), 2004. Gehlen, M., Bopp, L., Emprin, N., Aumont, O., Heinze, C., and Ragueneau, O.: Reconciling surface ocean productivity, export fluxes and sediment composition in a global biogeochemical ocean model, Biogeosciences, 3, 521–537, 2006. Govindasamy, B. and Caldeira, K.: Geoengineering Earth's radiation balance to mitigate CO₂-induced climate change, Geophys. Res. Lett., 27, 2141–2144, 2000. Hamwey, R. M.: Active amplification of the terrestrial albedo to mitigate climate change: An exploratory study, Mitigation and Adaptation Strategies for Global Change, 12, 419–439, 2007. Hansen, M. C., DeFries, R. S., Townshend, J. R. G., and Sohlberg, R.: Global land cover classification at 1 km spatial resolution using a classification tree approach, Int. J. Remote Sens., 21, 1331–1364, 2000. Harvey, L. D. D.: Mitigating the atmospheric CO₂ increase and ocean acidification by adding limestone powder to upwelling regions, J. Geophys. Res.-Oceans, 113, C04028, doi:10.1029/2007JC004373, 2008. Houghton, R. A.: Carbon Flux to the Atmosphere from Land-Use Changes: 1850–2005, in: TRENDS: A Compendium of Data on Global Change, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, US Department of Energy, Oak Ridge, Tennesee, USA, 2008. House, K. Z., Schrag, D. P., Harvey, C. F., and Lackner, K. S.: Permanent carbon dioxide storage in deep-sea sediments, Proc. Natl. Acad. Sci. USA, 103, 12 291–12 295, 2006. IPCC: Climate Change 2001: The Scientific Basis, Cambridge University Press, Cambridge, 881~pp., 2001. IPCC: Carbon Dioxide Capture and Storage, Cambridge University Press, Cambridge, 442~pp., 2005. IPCC: Climate Change 2007: The Physical Science Basis, Cambridge University Press, Cambridge, 996~pp., 2007. Jin, M., Dickinson, R. E., and Zhang, D.-L.: The Footprint of Urban Areas on Global Climate as Characterized by MODIS, J. Climate, 18, 1551–1565, 2005. Jin, X., Gruber, N., Frenzel, H., Doney, S. C., and McWilliams, J. C.: The impact on atmospheric CO₂ of iron fertilization induced changes in the ocean's biological pump, Biogeosciences, 5, 385–406, 2008. Joos, F., Bruno, M., Fink, R., Siegenthaler, U., Stocker, T. F., LeQuere, C., and Sarmiento, J. L.: An efficient and accurate representation of complex oceanic and biospheric models of anthropogenic carbon uptake, Tellus~B, 48, 397–417, 1996. Karl, D. M. and Letelier, R.: Nitrogen fixation-enhanced carbon sequestration in low nitrate, low chlorophyll seascapes, Mar. Ecol.-Prog. Ser., 364, 257–268, 2008. Keith, D. W., Ha-Doung, M., and Stolaroff, J. K.: Climate strategy with CO₂ capture from the air, Climatic Change, 74, 17–45, 2006. Kharecha, P. A. and Hansen, J. E.: Implications of "peak oil" for atmospheric CO₂ and climate, Global Biogeochem. Cy., 22, GB3012, 2008. Kheshgi, H. S.: Sequestering Atmospheric carbon dioxide by increasing ocean alkalinity, Energy, 20, 915–922, 1995. Kiehl, J. T. and Trenberth, K. E.: Earth's annual global mean energy budget, B. Am. Meteorol. Soc., 78, 197–208, 1997. Lampitt, R. S., Achterberg, E. P., Anderson, T. R., Hughes, J. A., Iglesias-Rodriguez, M. D., Kelly-Gerreyn, B. A., Lucas, M., Popove, E. E., Sanders, R., Shepherd, J. G., Smythe-Wright, D., and Yool, A.: Ocean fertilization: a potential means of geoengineering, Philos. T. R. Soc. A, 366(1882), 3919–3945, doi:10.1098/rsta.2008.0139, 2008. Latham, J.: Control of global warming?, Nature, 347, 339–340, 1990. Latham, J.: Amelioration of global warming by controlled enhancement of the albedo and longevity of low-level maritime clouds, Atmospheric Science Letters, 3, 52–58, 2002. Latham, J., Rasch, P., Chen, C.-C., Kettles, L., Gadian, A., Gettelman, A., Morrison, H., Bower, K., and Choularton, T.: Global temperature stabilization via controlled albedo enhancement of low-level maritime clouds, Philos. T. R. Soc. A, 366(1882), 3969–3987, doi:10.1098/rsta.2008.0137, 2008. Laws, E. A., Falkowski, P. G., Smith, W. O., Ducklow, H., and McCarthy, J. J.: Temperature effects on export production in the open ocean, Global Biogeochem. Cy., 14, 1231–1246, 2000. Leake, J. E.: "Biosphere carbon stock management: Addressing the threat of abrupt climate change in the next few decades." By Peter Read, An editorial comment., Climatic Change, 87, 329–334, 2008. Lehmann, J., Gaunt, J., and Rondon, M.: Bio-char sequestration in terrestrial ecosystems – a review, Mitigation and Adaptation Strategies for Global Change, 11, 403–427, 2006. Lenton, T. M.: Land and ocean carbon cycle feedback effects on global warming in a simple Earth system model, Tellus~B, 52, 1159–1188, doi:10.1034/j.1600-0889.2000.01104.x, 2000. Lenton, T. M. and Watson, A. J.: Redfield revisited: 1. Regulation of nitrate, phosphate and oxygen in the ocean, Global Biogeochem. Cy., 14, 225–248, 2000a. Lenton, T. M.: Climate Change to the end of the Millennium, Climatic Change, 76, 7–29, doi:10.1007/s10584-005-9022-1, 2006. Loveland, T. R., Reed, B. C., Brown, J. F., Ohlen, D. O., Zhu, Z., Yang, L., and Merchant, J. W.: Development of a global land cover characteristics database and IGBP DISCover from 1 km AVHRR data, Int. J. Remote Sens., 21, 1303–1330, 2000. Lovelock, J. E. and Rapley, C. G.: Ocean pipes could help the earth to cure itself, Nature, 449, p 403, 2007. MacCracken, M. C.: Geoengineering: Worthy of cautious evaluation?, Climatic Change, 77, 235–243, 2006. Mackenzie, F. T., Ver, L. M., and Lerman, A.: Century-scale nitrogen and phosphorus controls of the carbon cycle, Chem. Geol., 190, 13–32, 2002. Martin, J. H., Knauer, G. A., Karl, D. M., and Broenkow, W. W.: VERTEX: Carbon cycling in the northeast Pacific, Deep Sea-Res., 34, 267–285, 1987. Najjar, R. G., Jin, X., Louanchi, F., Aumont, O., Caldeira, K., Doney, S. C., Dutay, J.-C., Follows, M., Gruber, N., Joos, F., Lindsay, K., Maier-Reimer, E., Matear, R. J., Matsumoto, K., Monfray, P., Mouchet, A., Orr, J. C., Plattner, G.-K., Sarmiento, J. L., Schlitzer, R., Slater, R. D., Weirig, M.-F., Yamanaka, Y., and Yool, A.: Impact of circulation on export production, dissolved organic matter, and dissolved oxygen in the ocean: Results from Phase II of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2), Global Biogeochem. Cy., 21, GB3007, 10.1029/2006GB002857, 2007. NAS: Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base, Washington, DC, 918~pp., 1992. Oman, L., Robock, A., Stenchikov, G. L., Schmidt, G. A., and Ruedy, R.: Climatic response to high-latitude volcanic eruptions, J. Geophys. Res.-Atmos., 110, D13103, doi:10.1029/2004JD005487, 2005. Pacala, S. and Socolow, R.: Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies, Science, 305, 968–972, 2004. Pearson, J., Oldson, J., and Levin, E.: Earth rings for planetary environment control, Acta astronaut., 58, 44–57, 2006. Rasch, P. J., Crutzen, P. J., and Coleman, D. B.: Exploring the geoengineering of climate using stratospheric sulphate aerosols: The role of particle size, Geophys. Res. Lett., 35, L02809, doi:10.1029/2007GL032179, 2008. Raupach, M. R., Marland, G., Ciais, P., LeQuere, C., Canadell, J. G., Klepper, G., and Field, C. B.: Global and regional drivers of accelerating CO₂ emissions, Proceedings of the National Academy of Science, 104, 10 288–10 293, 2007. Read, P. and Lermit, J.: Bio-energy with carbon storage (BECS): A sequential decision approach to the threat of abrupt climate change, Energy, 30, 2654–2671, 2005. Read, P. and Parshotam, A.: Holistic greenhouse gas management strategy (with \mboxreviewers' comments and authors' rejoinders), Victoria University of Wellington, Wellington, New Zealand, available at: http://ips.ac.nz/publications/publications/show/205 (last access: 20 January 2009), 2007. Read, P.: Biosphere carbon stock management: addressing the threat of abrupt climate change in the next few decades: an editorial essay, Climatic Change, 87, 305–320, 2008. Redfield, A. C.: The biological control of chemical factors in the environment, Am. Sci., 46, 205–221, 1958. Ridgwell, A., Singarayer, J. S., Hetherington, A. M., and Valdes, P. J.: Tackling regional climate change by leaf albedo bio-geoengineering, Curr. Biol., 19, doi:10.1016/j.cub.2008.12.025, 2009. Robock, A., Oman, L., and Stenchikov, G. L.: Regional climate responses to geoengineering with tropical and Arctic SO₂ injections, J. Geophys. Res.-Atmos., 113, D16101, doi:10.1029/2008JD010050, 2008. Rosenfeld, A. H., Romm, J. J., Akbari, H., and LLoyd, A. C.: Painting the town white and green, Technol. Rev., 100, 52–59, 1997. Stenchikov, G. L., Kirchner, I., Robock, A., Graf, H. F., Antuna, J. C., Grainger, R. G., Lambert, A., and Thomason, L.: Radiative forcing from the 1991 mount Pinatubo volcanic eruption, J. Geophys. Res.-Atmos., 103, 13 837–13 857, 1998. Stern, N.: The Economics of Climate Change: The Stern Review, Cambridge University Press, Cambrige, 692~pp., 2006. Taha, H.: Urban surface modification as a potential ozone air-quality improvement strategy in California: a mesoscale modelling study, Bound.-Lay. Meteorol., 127, 219–239, 2008. Teller, E., Wood, L., and Hyde, R.: Global Warming and Ice Ages: I. Prospects For Physics Based Modulation of Global Change, Lawrence Livermore National Laboratory (LLNL), CA (USA), Preprint UCRL-JC-128715, 1997. Teller, E., Hyde, R., and Wood, L.: Active Climate Stabilization: Practical Physics-Based Approaches to Prevention of Climate Change, Lawrence Livermore National Laboratory (LLNL), CA (USA), Preprint UCRL-JC-148012, 2002. Tsvetsinskaya, E. A., Schaaf, C. B., Gao, F., Strahler, A. H., Dickinson, R. E., Zeng, X., and Lucht, W.: Relating MODIS-derived surface albedo to soils and rock types over Northern Africa and the Arabian peninsula, Geophys. Res. Lett., 29, 1353, doi:10.1029/2001GL014096, 2002. Twomey, S.: Aerosols, clouds and radiation, Atmos. Environ., 25A, 2435–2442, 1991. Vaughan, N. E. and Lenton, T. M.: A review of climate geoengineering proposals, Climatic Change, submitted, 2009. Vogt, M., Vallina, S., and von Glasow, R.: New directions: Correspondence on "enhancing the natural cycle to slow global warming", Atmos. Environ., 42, 4803–4805, 2008. Wigley, T. M. L.: A combined mitigation/geoengineering approach to climate stabilization, Science, 314, 452–454, 2006. Wingenter, O. W., Elliot, S. M., and Blake, D. R.: New directions: Enhancing the natural sulphur cycle to slow global warming, Atmos. Environ., 41, 7373–7375, 2007. Winjum, J. K., Dixon, R. K., and Schroeder, P. E.: Estimating the global potential of forest and agroforest management practices to sequester carbon, Water Air Soil Poll., 64, 213–227, 1992. Woodhouse, M. T., Mann, G. W., Carslaw, K. S., and Boucher, O.: New Directions: The impact of oceanic iron fertilisation on cloud condensation nuclei, Atmos. Environ., 42, 5728–5730, 2008. Zeebe, R. E. and Archer, D.: Feasibility of ocean fertilization and its impact on future atmospheric CO₂ levels, Geophys. Res. Lett., 32, L09703, doi:10.1029/2005GL022449, 2005. Zeman, F.: Energy and material balance of CO₂ capture from ambient air, Environ. Sci. Technol., 41, 7558–7563, 2007. Zhou, S. and Flynn, P. C.: Geoengineering downwelling ocean currents: A cost assessment, Climatic Change, 71, 203–220, 2005.