Editing IPCC:AR6/WGI/Chapter-6 (section)

==== 6.2.2.1 Lightning NO <sub>x</sub> ====

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Lightning contributes approximately 10% of the total NO <sub>x</sub> emissions ( [[#Murray--2016|Murray, 2016]] ). Since lightning NO <sub>x</sub> (LNO <sub>x</sub> ) is predominantly released in the upper troposphere, it has a disproportionately large impact on ozone and OH, and on the lifetime of methanecompared with surface NO <sub>x</sub> emissions. Whereas the global spatial and temporal distribution of lightning flashes can be characterized thanks to satellite-borne and ground sensors ( [[#Virts--2013|Virts et al., 2013]] ; [[#Cecil--2014|Cecil et al., 2014]] ), constraining the amount of NO <sub>x</sub> produced per flash (Miyazaki et al. , 2014; Medici et al. , 2017; Nault et al. , 2017; Marais et al. , 2018; D.J. Allen et al. , 2019; Bucsela et al. , 2019) and its vertical allocation ( [[#Koshak--2014|Koshak et al., 2014]] ; [[#Medici--2017|Medici et al., 2017]] ) has been more elusive.

Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) models in CMIP5 used a range of LNO <sub>x4</sub> between 1.2–9.7 TgN y <sup>−1</sup> (Lamarque et al., 2013b). In CMIP6, the corresponding LNO <sub>x</sub> range is between 3.2–7.6 TgN y <sup>−1</sup> ( [[#Griffiths--2021|Griffiths et al., 2021]] ). All CMIP6 models (as well as most models included in CMIP5, [[#Young--2013|Young et al., 2013]] ) apply a parametrization that relates cloud-top height to lightning intensity ( [[#Price--1992|Price and Rind, 1992]] ), projecting an increase in LNO <sub>x</sub> in a warmer world in the range of 0.27–0.61 TgN yr <sup>−1</sup> °C <sup>–1</sup> ( [[#Thornhill--2021a|Thornhill et al., 2021a]] ). However, models using parametrizations based on convection ( [[#Grewe--2001|Grewe et al., 2001]] ), updraft mass flux ( [[#Allen--2002|Allen and Pickering, 2002]] ) or ice flux ( [[#Finney--2016a|Finney et al., 2016a]] ) show either much less sensitivity or a negative response ( [[#Finney--2016b|Finney et al., 2016b]] , 2018; [[#Clark--2017|Clark et al., 2017]] ).

In summary, the total present-day global lightning NO <sub>x</sub> emissions are still estimated to be within a factor of two. There is ''high confidence'' that LNO <sub>x</sub> are perturbed by climate change; however, there is ''low confidence'' in the sign of the change due to fundamental uncertainties in parametrizations. <sub></sub>

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