Do Responses to Different Anthropogenic Forcings Add Linearly in Climate Models?

TitleDo Responses to Different Anthropogenic Forcings Add Linearly in Climate Models?
Publication TypeJournal Article
Year of Publication2015
Authors, LeGrande Allegra N., Nazarenko Larissa, and Tsigaridis Kostas
JournalEnvironmental Research Letters
Volume10
Number10
Pages104010
Date Published10/2015
Abstract / Summary

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. 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.

URLhttp://stacks.iop.org/1748-9326/10/i=10/a=104010
Journal: Environmental Research Letters
Year of Publication: 2015
Volume: 10
Number: 10
Pages: 104010
Date Published: 10/2015

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. 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.

Citation:
2015.  "Do Responses to Different Anthropogenic Forcings Add Linearly in Climate Models?"  Environmental Research Letters 10(10): 104010.