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Title: Do responses to different anthropogenic forcings add linearly in climate models?

Many detection and attribution and pattern scaling studies assume that the global climate response to multiple forcings is additive: that the response over the historical period is statistically indistinguishable from the sum of the responses to individual forcings. Here, we use the NASA Goddard Institute for Space Studies (GISS) and National Center for Atmospheric Research Community Climate System Model (CCSM4) simulations from the CMIP5 archive to test this assumption for multi-year trends in global-average, annual-average temperature and precipitation at multiple timescales. We find that responses in models forced by pre-computed aerosol and ozone concentrations are generally additive across forcings. However, we demonstrate that there are significant nonlinearities in precipitation responses to different forcings in a configuration of the GISS model that interactively computes these concentrations from precursor emissions. We attribute these to differences in ozone forcing arising from interactions between forcing agents. Lastly, our results suggest that attribution to specific forcings may be complicated in a model with fully interactive chemistry and may provide motivation for other modeling groups to conduct further single-forcing experiments.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [2] ;  [1] ;  [5]
  1. NASA GISS, New York, NY (United States); Columbia Univ., New York, NY (United States)
  2. NASA GISS, New York, NY (United States)
  3. Duke Univ., Durham, NC (United States)
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  5. Columbia Univ., New York, NY (United States)
Publication Date:
Report Number(s):
LLNL-JRNL-707578
Journal ID: ISSN 1748-9326
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Environmental Research Letters
Additional Journal Information:
Journal Volume: 10; Journal Issue: 10; Journal ID: ISSN 1748-9326
Publisher:
IOP Publishing
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; detection and attribution; radiative forcing; linearity
OSTI Identifier:
1332476

Marvel, Kate, Schmidt, Gavin A., Shindell, Drew, Bonfils, Celine, LeGrande, Allegra N., Nazarenko, Larissa, and Tsigaridis, Kostas. Do responses to different anthropogenic forcings add linearly in climate models?. United States: N. p., Web. doi:10.1088/1748-9326/10/10/104010.
Marvel, Kate, Schmidt, Gavin A., Shindell, Drew, Bonfils, Celine, LeGrande, Allegra N., Nazarenko, Larissa, & Tsigaridis, Kostas. Do responses to different anthropogenic forcings add linearly in climate models?. United States. doi:10.1088/1748-9326/10/10/104010.
Marvel, Kate, Schmidt, Gavin A., Shindell, Drew, Bonfils, Celine, LeGrande, Allegra N., Nazarenko, Larissa, and Tsigaridis, Kostas. 2015. "Do responses to different anthropogenic forcings add linearly in climate models?". United States. doi:10.1088/1748-9326/10/10/104010. https://www.osti.gov/servlets/purl/1332476.
@article{osti_1332476,
title = {Do responses to different anthropogenic forcings add linearly in climate models?},
author = {Marvel, Kate and Schmidt, Gavin A. and Shindell, Drew and Bonfils, Celine and LeGrande, Allegra N. and Nazarenko, Larissa and Tsigaridis, Kostas},
abstractNote = {Many detection and attribution and pattern scaling studies assume that the global climate response to multiple forcings is additive: that the response over the historical period is statistically indistinguishable from the sum of the responses to individual forcings. Here, we use the NASA Goddard Institute for Space Studies (GISS) and National Center for Atmospheric Research Community Climate System Model (CCSM4) simulations from the CMIP5 archive to test this assumption for multi-year trends in global-average, annual-average temperature and precipitation at multiple timescales. We find that responses in models forced by pre-computed aerosol and ozone concentrations are generally additive across forcings. However, we demonstrate that there are significant nonlinearities in precipitation responses to different forcings in a configuration of the GISS model that interactively computes these concentrations from precursor emissions. We attribute these to differences in ozone forcing arising from interactions between forcing agents. Lastly, our results suggest that attribution to specific forcings may be complicated in a model with fully interactive chemistry and may provide motivation for other modeling groups to conduct further single-forcing experiments.},
doi = {10.1088/1748-9326/10/10/104010},
journal = {Environmental Research Letters},
number = 10,
volume = 10,
place = {United States},
year = {2015},
month = {10}
}