Trends in global tropospheric hydroxyl radical and methane lifetime since 1850 from AerChemMIP
<p>We analyse historical (1850–2014) atmospheric hydroxyl (OH) and methane lifetime data from Coupled Model Intercomparison Project Phase 6 (CMIP6)/Aerosols and Chemistry Model Intercomparison Project (AerChemMIP) simulations. Tropospheric OH changed little from 1850 up to around 1980, then in...
Main Authors: | , , , , , , , , , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2020-11-01
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Series: | Atmospheric Chemistry and Physics |
Online Access: | https://acp.copernicus.org/articles/20/12905/2020/acp-20-12905-2020.pdf |
Summary: | <p>We analyse historical (1850–2014) atmospheric hydroxyl
(OH) and methane lifetime data from Coupled Model Intercomparison Project
Phase 6 (CMIP6)/Aerosols and Chemistry Model Intercomparison Project
(AerChemMIP) simulations. Tropospheric OH changed little from 1850 up to
around 1980, then increased by around 9 % up to 2014, with an associated
reduction in methane lifetime. The model-derived OH trends from 1980 to 2005
are broadly consistent with trends estimated by several studies that infer
OH from inversions of methyl chloroform and associated measurements; most
inversion studies indicate decreases in OH since 2005. However, the model
results fall within observational uncertainty ranges. The upward trend in
modelled OH since 1980 was mainly driven by changes in anthropogenic
near-term climate forcer emissions (increases in anthropogenic nitrogen
oxides and decreases in CO). Increases in halocarbon emissions since 1950
have made a small contribution to the increase in OH, whilst increases in
aerosol-related emissions have slightly reduced OH. Halocarbon emissions
have dramatically reduced the stratospheric methane lifetime by about
15 %–40 %; most previous studies assumed a fixed stratospheric lifetime.
Whilst the main driver of atmospheric methane increases since 1850 is
emissions of methane itself, increased ozone precursor emissions have
significantly modulated (in general reduced) methane trends. Halocarbon and
aerosol emissions are found to have relatively small contributions to
methane trends. These experiments do not isolate the effects of climate
change on OH and methane evolution; however, we calculate residual terms that
are due to the combined effects of climate change and non-linear
interactions between drivers. These residual terms indicate that non-linear
interactions are important and differ between the two methodologies we use
for quantifying OH and methane drivers. All these factors need to be
considered in order to fully explain OH and methane trends since 1850; these
factors will also be important for future trends.</p> |
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ISSN: | 1680-7316 1680-7324 |