Radiative forcing of climate change from the Copernicus reanalysis of atmospheric composition

Abstract

Abstract. Radiative forcing provides an important basis for understanding and predicting global climate changes, but its quantification has historically been done independently for different forcing agents, involved observations to varying degrees, and studies have not always included a detailed analysis of uncertainties. The Copernicus Atmosphere Monitoring Service reanalysis is an optimal combination of modelling and observations of atmospheric composition. It provides a unique opportunity to rely on observations to quantify the monthly- and spatially-resolved global distributions of radiative forcing consistently for six of the largest forcing agents: carbon dioxide, methane, tropospheric ozone, stratospheric ozone, aerosol-radiation interactions, and aerosol-cloud interactions. These radiative forcing estimates account for adjustments in stratospheric temperatures, but do not account for rapid adjustments in the troposphere. On a global average and over the period 2003–2016, stratospherically adjusted radiative forcing of carbon dioxide has averaged +1.84 W m−2 (5–95% confidence interval: 1.46 to 2.22 W m−2) relative to 1750 and increased at a rate of 17 % per decade. The corresponding values for methane are +0.45 (0.35 to 0.55) W m−2 and 3 % per decade, but with a clear acceleration since 2007. Ozone radiative forcing averages +0.32 (0 to 0.64) W m−2 and aerosol radiative forcing averages −1.37 (−2.17 to −0.57) W m−2. Both have been relatively stable since 2003. Taking the six forcing agents together, there no indication of a slowdown or acceleration in the rate of increase in anthropogenic radiative forcing over the period. These ongoing radiative forcing estimates will monitor the impact on the Earth’s energy budget of the dramatic emission reductions towards net-zero that are needed to limit surface temperature warming to the Paris Agreement temperature targets. Indeed, such impacts should be clearly manifested in radiative forcing before being clear in the temperature record. In addition, this radiative forcing dataset can provide the input distributions needed by researchers involved in monitoring of climate change, detection and attribution, interannual to decadal prediction, and integrated assessment modelling. The data generated by this work are available at https://doi.org/10.24380/ads.1hj3y896 (Bellouin et al., 2020).

Energy Budget Constraints on the Time History of Aerosol Forcing and Climate Sensitivity

“…Our best estimate 1750–2019 aerosol forcing of −0.90 W m −2 is similar to recent observationally constrained studies that put aerosol forcing in the −0.8 to −0.9 W m −2 range (Andrews & Forster, 2020; Skeie et al., 2018; Smith, Forster, et al., 2018), and the review of 19 inverse estimates in Forest (2018) of −0.77 W m −2 . We also find that the most likely shape of recent (1980–2014) aerosol forcing is approximately constant or with a slightly positive trend, which is in line with reanalysis‐derived estimates of aerosol RFari and RFaci (Bellouin, Davies, et al., 2020), and a rapid recovery in aerosol forcing is not likely.…”

“…Skeie et al, 2018;, and the review of 19 inverse estimates in Forest (2018) of −0.77 W m −2 . We also find that the most likely shape of recent aerosol forcing is approximately constant or with a slightly positive trend, which is in line with reanalysis-derived estimates of aerosol RFari and RFaci (Bellouin, Davies, et al, 2020), and a rapid recovery in aerosol forcing is not likely. SMITH ET AL.…”

Changes in Clear‐Sky Shortwave Aerosol Direct Radiative Effects Since 2002

“…Since the CERES results do not show this unexpected behavior, we cannot exclude MODIS calibration drift as a possible cause, as recently suggested by Bellouin, Davies, et al. (2020), who found similar results. On the other hand, if the SH AOD trends are real and are due to anthropogenic aerosols transported to the Southern Ocean, this would have important implications to aerosol radiative forcing.…”

Constraining the Twomey effect from satellite observations: Issues and perspectives

“…Such aerosol re-analysis information has been used for assessing RF aci in several studies (Bellouin et al, 2013;McCoy et al, 2017;Bellouin et al, 2020a). However, assessing the validity of model results requires extensive and rigorous evaluation, especially for coarsely-resolved models with regard to aerosol scavenging below clouds.…”