Editing IPCC:AR6/WGIII/Chapter-4 (section)

==== 4.2.5.12 Ambitious Targets to Reduce Short-lived Climate Forcers, Including Methane ====

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Recent research shows that temperature increases are likely to exceed 1.5°C during the 2030s and 2°C by mid-century unless both CO 2 and short-lived climate forcers (SLCFs) are reduced ( [[#Shindell--2017|Shindell et al. 2017]] ; [[#Rogelj--2018a|Rogelj et al. 2018a]] ). Because of their short lifetimes (days to a decade and a half), SLCFs can provide fast mitigation, potentially avoiding warming of up to 0.6°C at 2050 and up to 1.2°C at 2100 ( [[#Ramanathan--2010|Ramanathan and Xu 2010]] ; [[#Xu--2017|Xu and Ramanathan 2017]] ). In Asia especially, co-benefits of drastic CO 2 and air pollution mitigation measures reduce emissions of methane, black carbon, sulphur dioxide, nitrogen oxide, and fine particulate matter by approximately 23%, 63%, 73%, 27%, and 65% respectively in 2050 as compared to 2010 levels. Including the co-benefits of reduction of climate forcing adds significantly to the benefits reducing air pollutants ( [[#Hanaoka--2018|Hanaoka and Masui 2018]] ).

To achieve net zero GHG emissions implies consideration of targets for non-CO 2 gases. While methane emissions have grown less rapidly than CO 2 and F-gases since 1990 (Chapter 2), the literature urges action to bring methane back to a pathway more in line with the Paris goals ( [[#Nisbet--2020|Nisbet et al. 2020]] ). Measures to reduce methane emissions from anthropogenic sources are considered intractable – where they sustain livelihoods – but also becoming more feasible, as studies report the options for mitigation in agriculture without undermining food security ( [[#Wollenberg--2016|Wollenberg et al. 2016]] ; [[#Frank--2017|Frank et al. 2017]] ; [[#Nisbet--2020|Nisbet et al. 2020]] ). The choice of emission metrics has implications for SLCF ( [[#Cain--2019|Cain et al. 2019]] ) (Cross-Chapter Box 2 in Chapter 2). Ambitious reductions of methane are complementary to, rather than substitutes for, reductions in CO 2 ( [[#Nisbet--2020|Nisbet et al. 2020]] ).

Rapid SLCF reductions, specifically of methane, black carbon, and tropospheric ozone have immediate co-benefits including meeting sustainable development goals for reducing health burdens of household air pollution and reversing health- and crop-damaging tropospheric ozone ( [[#Jacobson--2002|Jacobson 2002]] , 2010). SLCF mitigation measures can have regional impacts, including avoiding premature deaths in Asia and Africa and warming in central and northern Asia, southern Africa, and the Mediterranean ( [[#Shindell--2012|Shindell et al. 2012]] ). Reducing outdoor air pollution could avoid 2.4 million premature deaths and 52 million tonnes of crop losses for four major staples ( [[#Haines--2017|Haines et al. 2017]] ). Existing research emphasises climate and agriculture benefits of methane mitigation measures with relatively small human health benefits ( [[#Shindell--2012|Shindell et al. 2012]] ). Research also predicts that black carbon mitigation could substantially benefit global climate and human health, but there is more uncertainty about these outcomes than about some other predictions ( [[#Shindell--2012|Shindell et al. 2012]] ). Other benefits to SLCF reduction include reducing warming in the critical near term, which will slow amplifying feedbacks, reduce the risk of non-linear changes, and reduce long-term cumulative climate impacts – like sea-level rise – and mitigation costs ( [[#Hu--2017|Hu et al. 2017]] ; [[#UNEP%20and%20WMO--2011|UNEP and WMO 2011]] ; [[#Rogelj--2018a|Rogelj et al. 2018a]] ; [[#Xu--2017|Xu and Ramanathan 2017]] ; [[#Shindell--2012|Shindell et al. 2012]] ).

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