Original Paper

Surveys in Geophysics

, Volume 27, Issue 5, pp 491-544

Quantifying anthropogenic influence on recent near-surface temperature change

  • M. R. AllenAffiliated withAtmospheric, Oceanic and Planetary Physics, University of Oxford Clarendon Laboratory Email author 
  • , N. P. GillettAffiliated withSchool of Earth and Ocean Sciences, University of VictoriaClimate Research Unit, School of Environmental Sciences, University of East Anglia
  • , J. A. KettleboroughAffiliated withSpace Science and Technology Department, Rutherford Appleton Laboratory Met. Office
  • , G. HegerlAffiliated withNicholas School for the Environment and Earth Sciences, Duke University
  • , R. SchnurAffiliated withMax Planck Institute for Meteorology
  • , P. A. StottAffiliated withMet Office, Reading Unit, Dept. of Meteorology, University of Reading
  • , G. BoerAffiliated withThe Canadian Centre for Climate Modelling and Analysis
  • , C. CoveyAffiliated withAtmospheric, Oceanic and Planetary Physics, University of Oxford Clarendon LaboratoryPCMDI, Lawrence Livermore National Laboratory
  • , T. L. DelworthAffiliated withAtmospheric, Oceanic and Planetary Physics, University of Oxford Clarendon LaboratoryNOAA Geophysical Fluid Dynamics Laboratory
    • , G. S. JonesAffiliated with Met. Office
    • , J. F. B. MitchellAffiliated with Met. Office
    • , T. P. BarnettAffiliated withAtmospheric, Oceanic and Planetary Physics, University of Oxford Clarendon LaboratoryScripps Institution for Oceanography, University of California

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Abstract

We assess the extent to which observed large-scale changes in near-surface temperatures over the latter half of the twentieth century can be attributed to anthropogenic climate change as simulated by a range of climate models. The hypothesis that observed changes are entirely due to internal climate variability is rejected at a high confidence level independent of the climate model used to simulate either the anthropogenic signal or the internal variability. Where the relevant simulations are available, we also consider the alternative hypothesis that observed changes are due entirely to natural external influences, including solar variability and explosive volcanic activity. We allow for the possibility that feedback processes, other than those simulated by the models considered, may be amplifying the observed response to these natural influences by an unknown amount. Even allowing for this possibility, the hypothesis of no anthropogenic influence can be rejected at the 5% level in almost all cases. The influence of anthropogenic greenhouse gases emerges as a substantial contributor to recent observed climate change, with the estimated trend attributable to greenhouse forcing similar in magnitude to the total observed warming over the 20th century. Much greater uncertainty remains in the response to other external influences on climate, particularly the response to anthropogenic sulphate aerosols and to solar and volcanic forcing. Our results remain dependent on model-simulated signal patterns and internal variability, and would benefit considerably from a wider range of simulations, particularly of the responses to natural external forcing.

Keywords

Climate change Detection Attribution