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8.1: How Long Can We Wait to Act

  • Page ID
    11182
  • Carbon dioxide is a greenhouse gas of special concern because of its long residence time in the atmosphere. The left panel of Figure \(\PageIndex{1}\) shows estimates of the evolution of CO2 assuming that emissions abruptly stop when concentrations reach various values. Over the first 100 years or so, concentrations fall fairly rapidly, but then the rate of decay drops off and it will take many thousands of years for concentrations to return to preindustrial values. Figure \(\PageIndex{2}\) shows projections of global mean temperature that correspond to the a pulse of CO2 concentration bringing the atmosphere to  500 ppm as shown in Figure \(\PageIndex{1}\). Curiously, the temperature hardly drops at all over the first thousand or so years after emissions cease, reflecting mostly the effects of heat storage in the oceans.

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    Figure \(\PageIndex{1}\): Evolution of atmospheric CO2 over time starting from a pulse that brings concetrations to ~ 500 ppm. Natural processes begin to relax concentrations back toward preindustrial values at the cessation of emissions. (CC-BY, Atmos. Chem. Phys., 13, 2793–2825, 2013. Joos, et al.)

    Curiously, the temperature hardly drops at all over the first thousand or so years after emissions cease, reflecting mostly the effects of heat storage in the oceans.

    clipboard_ec9efd256c9a88d5bebc860d5c241a657.png

    Figure \(\PageIndex{2}\): Surface temperature and ocean heat content as a function of time in the first millenia after a pulse setting CO2concentration to 500 ppm (CC-BY, Atmos. Chem. Phys., 13, 2793–2825, 2013. Joos, et al.)

    This is a crucial aspect of the challenge we face: absent technology for removing CO2 from the atmosphere, we will have to live with altered climate for many thousands of years. Thus we have a narrow time window within which to act.

     

    Reference:

    Joos, F., Roth, R., Fuglestvedt, J. S., Peters, G. P., Enting, I. G., von Bloh, W., Brovkin, V., Burke, E. J., Eby, M., Edwards, N. R., Friedrich, T., Frölicher, T. L., Halloran, P. R., Holden, P. B., Jones, C., Kleinen, T., Mackenzie, F. T., Matsumoto, K., Meinshausen, M., Plattner, G.-K., Reisinger, A., Segschneider, J., Shaffer, G., Steinacher, M., Strassmann, K., Tanaka, K., Timmermann, A., and Weaver, A. J.: Carbon dioxide and climate impulse response functions for the computation of greenhouse gas metrics: a multi-model analysis, Atmos. Chem. Phys., 13, 2793–2825, https://doi.org/10.5194/acp-13-2793-2013, 2013.

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