The effect of rapid adjustments to halocarbons and N2O on radiative forcing

Rapid adjustments occur after initial perturbation of an external climate driver (e.g., CO2) and involve changes in, e.g. atmospheric temperature, water vapour and clouds, independent of sea surface temperature changes. Knowledge of such adjustments is necessary to estimate effective radiative forci...

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Bibliographic Details
Published in:npj Climate and Atmospheric Science
Main Authors: Hodnebrog, Ø., Myhre, G., Kramer, R.J., Shine, K.P., Andrews, T., Faluvegi, G., Kasoar, M., Kirkevåg, A., Lamarque, J.-F., Mülmenstädt, J., Olivié, D., Samset, B.H., Shindell, D., Smith, C., Takemura, T., Voulgarakis, A.
Format: Article in Journal/Newspaper
Language:English
Published: 2020
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Online Access:https://pure.iiasa.ac.at/id/eprint/16850/
https://pure.iiasa.ac.at/id/eprint/16850/1/s41612-020-00150-x.pdf
https://doi.org/10.1038/s41612-020-00150-x
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Summary:Rapid adjustments occur after initial perturbation of an external climate driver (e.g., CO2) and involve changes in, e.g. atmospheric temperature, water vapour and clouds, independent of sea surface temperature changes. Knowledge of such adjustments is necessary to estimate effective radiative forcing (ERF), a useful indicator of surface temperature change, and to understand global precipitation changes due to different drivers. Yet, rapid adjustments have not previously been analysed in any detail for certain compounds, including halocarbons and N2O. Here we use several global climate models combined with radiative kernel calculations to show that individual rapid adjustment terms due to CFC-11, CFC-12 and N2O are substantial, but that the resulting flux changes approximately cancel at the top-of-atmosphere due to compensating effects. Our results further indicate that radiative forcing (which includes stratospheric temperature adjustment) is a reasonable approximation for ERF. These CFCs lead to a larger increase in precipitation per kelvin surface temperature change (2.2 ± 0.3% K−1) compared to other well-mixed greenhouse gases (1.4 ± 0.3% K−1 for CO2). This is largely due to rapid upper tropospheric warming and cloud adjustments, which lead to enhanced atmospheric radiative cooling (and hence a precipitation increase) and partly compensate increased atmospheric radiative heating (i.e. which is associated with a precipitation decrease) from the instantaneous perturbation. Ozone-depleting halocarbons and nitrous oxide (N2O) are well-mixed greenhouse gases that have contributed substantially to radiative forcing (RF) since pre-industrial time, by 0.33 ± 0.03 W m−2 (0.18 ± 0.17 W m−2 when including stratospheric ozone depletion) and 0.17 ± 0.03 W m−2, respectively1. A substantial contribution to global warming and Arctic sea-ice loss in the latter half of the 20th century was recently attributed to ozone-depleting substances2,3. Atmospheric lifetimes of chlorofluorocarbons (CFCs), an important group of ...