Abstract
Human activity has led to increased atmospheric concentrations of many gases, including halocarbons, and may lead to emissions of many more gases. Many of these gases are, on a per molecule basis, powerful greenhouse gases, although at present‐day concentrations their climate effect is in the so‐called weak limit (i.e., their effect scales linearly with concentration). We published a comprehensive review of the radiative efficiencies (RE) and global warming potentials (GWP) for around 200 such compounds in 2013 (Hodnebrog et al., 2013, https://doi.org/10.1002/rog.20013). Here we present updated RE and GWP values for compounds where experimental infrared absorption spectra are available. Updated numbers are based on a revised “Pinnock curve”, which gives RE as a function of wave number, and now also accounts for stratospheric temperature adjustment (Shine & Myhre, 2020, https://doi.org/10.1029/2019MS001951). Further updates include the implementation of around 500 absorption spectra additional to those in the 2013 review and new atmospheric lifetimes from the literature (mainly from WMO (2019)). In total, values for 60 of the compounds previously assessed are based on additional absorption spectra, and 42 compounds have REs which differ by >10% from our previous assessment. New RE calculations are presented for more than 400 compounds in addition to the previously assessed compounds, and GWP calculations are presented for a total of around 250 compounds. Present‐day radiative forcing due to halocarbons and other weak absorbers is 0.38 [0.33–0.43] W m−2, compared to 0.36 [0.32–0.40] W m−2 in IPCC AR5 (Myhre et al., 2013, https://doi.org/10.1017/CBO9781107415324.018), which is about 18% of the current CO2 forcing.
Highlights
Anthropogenic forcing of climate change is one of the most important challenges facing humanity
We limit this section to only include studies and spectra that were not included in H2013, and only to the 40 most abundant halocarbons presented in Table 7 of Meinshausen et al (2017)
We present a comprehensive assessment of the radiative efficiencies and global warming potentials (GWP) for a large number of halocarbons and other weak atmospheric absorbers
Summary
Anthropogenic forcing of climate change is one of the most important challenges facing humanity. The largest contributor to radiative forcing of climate change is the increased levels of greenhouse gases such as CO2, N2O, CH4, and halocarbons and related compounds. Protocol from 1987 and its amendments and adjustments, halocarbons still make an important contribution to radiative forcing of climate change because many have long atmospheric lifetimes. In 2013 we reviewed the literature data and provided a comprehensive and self‐consistent set of new calculations of REs and GWPs for halocarbons and related compounds (Hodnebrog et al, 2013, hereafter referred to as H2013). Additional infrared absorption spectra and refinements in estimations of the atmospheric lifetimes of halocarbons and other compounds have become available since our last review. Updates are based on new absorption spectra for 60 compounds considered in our previous review, the latest estimates of atmospheric lifetimes, and an update to the RE calculation method. The present work is the most comprehensive review of the radiative efficiencies and GWPs of halogenated compounds performed to date
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