Publication Abstracts

Smith et al. 2020, submitted

Smith, C.J., R.J. Kramer, G. Myhre, K. Alterskjær, W. Collins, A. Sima, O. Boucher, J.-L. Dufresne, P. Nabat, M. Michou, S. Yukimoto, J. Cole, D. Paynter, H. Shiogama, F.M. O'Connor, E. Robertson, A. Wiltshire, T. Andrews, C. Hannay, R.L. Miller, L. Nazarenko, A. Kirkevåg, D. Olivié, S. Fiedler, R. Pincus, and P.M. Forster, 2020: Effective radiative forcing and adjustments in CMIP6 models. Atmos. Chem. Phys., submitted, doi:10.5194/acp-2019-1212.

The effective radiative forcing, which includes the instantaneous forcing plus adjustments from the atmosphere and surface, has emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective radiative forcing and adjustments in 13 contemporary climate models that are participating in CMIP6 and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global mean anthropogenic forcing relative to pre-industrial (1850) from climate models stands at 1.97 (±0.26) W/m2, comprised of 1.80 (±0.11) W/m2 from CO2, 1.07 (±0.21) W/m2 from other well-mixed greenhouse gases, -1.04 (±0.23) W/m2 from aerosols and -0.08 (±0.14) W/m2 from land use change. Quoted uncertainties are one standard deviation across model best estimates, and 90% confidence in the reported forcings, due to internal variability, is typically within 0.1 W/m2. The majority of the remaining 0.17 W/m2 is likely to be from ozone. As determined in previous studies, cancellation of tropospheric and surface adjustments means that the traditional stratospherically adjusted radiative forcing is approximately equal to ERF for greenhouse gas forcing, but not for aerosols, and consequentially, not for the anthropogenic total. The spread of aerosol forcing ranges from -0.63 to -1.37 W/m2, exhibiting a less negative mean and narrower range compared to 10 CMIP5 models. The spread in 4×CO2 forcing has also narrowed in CMIP6 compared to 13 CMIP5 models. Aerosol forcing is uncorrelated with equilibrium climate sensitivity. Therefore, there is no evidence to suggest that the increasing spread in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol forcing.

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BibTeX Citation

@unpublished{sm03200x,
  author={Smith, C. J. and Kramer, R. J. and Myhre, G. and Alterskjær, K. and Collins, W. and Sima, A. and Boucher, O. and Dufresne, J.-L. and Nabat, P. and Michou, M. and Yukimoto, S. and Cole, J. and Paynter, D. and Shiogama, H. and O'Connor, F. M. and Robertson, E. and Wiltshire, A. and Andrews, T. and Hannay, C. and Miller, R. L. and Nazarenko, L. and Kirkevåg, A. and Olivié, D. and Fiedler, S. and Pincus, R. and Forster, P. M.},
  title={Effective radiative forcing and adjustments in CMIP6 models},
  year={2020},
  journal={Atmos. Chem. Phys.},
  doi={10.5194/acp-2019-1212},
  note={Manuscript submitted for publication}
}

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RIS Citation

TY  - UNPB
ID  - sm03200x
AU  - Smith, C. J.
AU  - Kramer, R. J.
AU  - Myhre, G.
AU  - Alterskjær, K.
AU  - Collins, W.
AU  - Sima, A.
AU  - Boucher, O.
AU  - Dufresne, J.-L.
AU  - Nabat, P.
AU  - Michou, M.
AU  - Yukimoto, S.
AU  - Cole, J.
AU  - Paynter, D.
AU  - Shiogama, H.
AU  - O'Connor, F. M.
AU  - Robertson, E.
AU  - Wiltshire, A.
AU  - Andrews, T.
AU  - Hannay, C.
AU  - Miller, R. L.
AU  - Nazarenko, L.
AU  - Kirkevåg, A.
AU  - Olivié, D.
AU  - Fiedler, S.
AU  - Pincus, R.
AU  - Forster, P. M.
PY  - 2020
TI  - Effective radiative forcing and adjustments in CMIP6 models
JA  - Atmos. Chem. Phys.
DO  - 10.5194/acp-2019-1212
ER  -

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