EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Climate forcing and committed global warming: GHGs, aerosols and ozone 1970-2010

Alcide Zhao, David Stevenson, and Massimi Bollasina
Alcide Zhao et al.
  • The University of Edinburgh, School of GeoSciences, EDINBURGH, United Kingdom of Great Britain and Northern Ireland (

It is crucial to reduce uncertainties in our understanding of the climate impacts of short‐lived climate forcers, in the context that their emissions/concentrations are anticipated to decrease significantly in the coming decades worldwide. Using the Community Earth System Model (CESM1), we performed time‐slice experiments to investigate the effective radiative forcing (ERF) and climate respons to 1970–2010 changes in well‐mixed greenhouse gases (GHGs), anthropogenic aerosols, and tropospheric and stratospheric ozone. Once the present‐day climate has fully responded to 1970–2010 changes in all forcings, both the global mean temperature and precipitation responses are twice as large as the transient ones, with wet regions getting wetter and dry regions drier. The temperature response per unit ERF for short‐lived species varies considerably across many factors including forcing agents and the magnitudes and locations of emission changes. This suggests that the ERF should be used carefully to interpret the climate impacts of short‐lived climate forcers. Changes in both the mean and the probability distribution of global mean daily precipitation are driven mainly by GHG increases. However, changes in the frequency distributions of regional mean daily precipitation are more strongly influenced by changes in aerosols, rather than GHGs. This is particularly true over Asia and Europe where aerosol changes have significant impacts on the frequency of heavy‐to‐extreme precipitation. Our results may help guide more reliable near‐future climate projections and allow us to manage climate risks more effectively.

How to cite: Zhao, A., Stevenson, D., and Bollasina, M.: Climate forcing and committed global warming: GHGs, aerosols and ozone 1970-2010, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19702,, 2020

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Presentation version 1 – uploaded on 30 Apr 2020
  • CC1: Comment on EGU2020-19702, Greg Kopp, 06 May 2020

    Nice, clear presentation! Looks like a ~150-year time constant for thermal response, largely driven by ocean response rates. Do you know the time constant for land only?

    Thanks! Greg

  • CC2: Comment on EGU2020-19702, Luis Sánchez , 06 May 2020

    Thank you very much for this interesting work. Here are my questions:

    1. Would naturally-emitted short-lived brominated or iodinated compounds (ozone-depleting substances) have a significant impact in climate forcing or GWP calculations that is still not addressed by models? 

    2. Regarding the climate dimension of the  iodine  oxide particles (IOPs) (e.g. from naturally-emitted iodocarbons), would they be incorporated into the models? According to Cuevas et al (2018),  iodine levels have  tripled over the North Atlantic since 1950, so these aerosols may be relevant.