Articles | Volume 13, issue 5
Atmos. Chem. Phys., 13, 2793–2825, 2013
Atmos. Chem. Phys., 13, 2793–2825, 2013

Research article 08 Mar 2013

Research article | 08 Mar 2013

Carbon dioxide and climate impulse response functions for the computation of greenhouse gas metrics: a multi-model analysis

F. Joos1,2, R. Roth1,2, J. S. Fuglestvedt3, G. P. Peters3, I. G. Enting4, W. von Bloh5, V. Brovkin6, E. J. Burke7, M. Eby8, N. R. Edwards9, T. Friedrich10, T. L. Frölicher1,11, P. R. Halloran7, P. B. Holden9, C. Jones7, T. Kleinen6, F. T. Mackenzie12, K. Matsumoto13, M. Meinshausen5,14, G.-K. Plattner1, A. Reisinger15, J. Segschneider6, G. Shaffer16,17, M. Steinacher1,2, K. Strassmann1,2, K. Tanaka18, A. Timmermann10, and A. J. Weaver8 F. Joos et al.
  • 1Climate and Environmental Physics, Physics Institute, University of Bern, Bern, Switzerland
  • 2Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
  • 3Center for International Climate and Environmental Research – Oslo (CICERO), P.O. Box 1129 Blindern, 0318 Oslo, Norway
  • 4MASCOS, 139 Barry St, The University of Melbourne, Vic 3010, Australia
  • 5Potsdam Institute for Climate Impact Research, P.O. Box 601203, 14412, Potsdam, Germany
  • 6Max Planck Institute for Meteorology, Bundesstr. 53, 20146 Hamburg, Germany
  • 7Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, UK
  • 8School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
  • 9The Open University, Environment, Earth and Ecosystems, Milton Keynes, UK
  • 10International Pacific Research Center, School of Ocean and Earth Science and Technology, University of Hawaii, 1680 East-West Rd. Honolulu, HI, USA
  • 11AOS Program, Princeton University, Princeton, NJ, USA
  • 12Department of Oceanography, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii, 96822, USA
  • 13Department of Earth Sciences, University of Minnesota, Minneapolis, MN, USA
  • 14School of Earth Sciences, The University of Melbourne, VIC, Australia
  • 15New Zealand Agricultural Greenhouse Gas Research Centre, Palmerston North 4442, New Zealand
  • 16Department of Geophysics, University of Concepcion, Chile
  • 17Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
  • 18Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland

Abstract. The responses of carbon dioxide (CO2) and other climate variables to an emission pulse of CO2 into the atmosphere are often used to compute the Global Warming Potential (GWP) and Global Temperature change Potential (GTP), to characterize the response timescales of Earth System models, and to build reduced-form models. In this carbon cycle-climate model intercomparison project, which spans the full model hierarchy, we quantify responses to emission pulses of different magnitudes injected under different conditions. The CO2 response shows the known rapid decline in the first few decades followed by a millennium-scale tail. For a 100 Gt-C emission pulse added to a constant CO2 concentration of 389 ppm, 25 ± 9% is still found in the atmosphere after 1000 yr; the ocean has absorbed 59 ± 12% and the land the remainder (16 ± 14%). The response in global mean surface air temperature is an increase by 0.20 ± 0.12 °C within the first twenty years; thereafter and until year 1000, temperature decreases only slightly, whereas ocean heat content and sea level continue to rise. Our best estimate for the Absolute Global Warming Potential, given by the time-integrated response in CO2 at year 100 multiplied by its radiative efficiency, is 92.5 × 10−15 yr W m−2 per kg-CO2. This value very likely (5 to 95% confidence) lies within the range of (68 to 117) × 10−15 yr W m−2 per kg-CO2. Estimates for time-integrated response in CO2 published in the IPCC First, Second, and Fourth Assessment and our multi-model best estimate all agree within 15% during the first 100 yr. The integrated CO2 response, normalized by the pulse size, is lower for pre-industrial conditions, compared to present day, and lower for smaller pulses than larger pulses. In contrast, the response in temperature, sea level and ocean heat content is less sensitive to these choices. Although, choices in pulse size, background concentration, and model lead to uncertainties, the most important and subjective choice to determine AGWP of CO2 and GWP is the time horizon.

Final-revised paper