Editing IPCC:AR6/SYR/Longer-Report (section)

==== 3.3.4 Overshoot Pathways: Increased Risks and Other Implications ====

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'''Exceeding a specific remaining carbon budget results in higher global warming. Achieving and sustaining net negative global CO''' '''2''' '''emissions could reverse the resulting temperature exceedance (''' '''''high confidence)''''' '''''.''''' Continued reductions in emissions of short-lived climate forcers, particularly methane, after peak temperature has been reached, would also further reduce warming ( ''high confidence'' ). Only a small number of the most ambitious global modelled pathways limit global warming to 1.5°C (&gt;50%) without overshoot. { ''WGI SPM D.1.1, WGI SPM D.1.6, WGI SPM D.1.7; WGIII TS.4.2'' }

Overshoot of a warming level results in more adverse impacts, some irreversible, and additional risks for human and natural systems compared to staying below that warming level, with risks growing with the magnitude and duration of overshoot ( ''high confidence'' ). Compared to pathways without overshoot, societies and ecosystems would be exposed to greater and more widespread changes in climatic impact-drivers, such as extreme heat and extreme precipitation, with increasing risks to infrastructure, low-lying coastal settlements, and associated livelihoods ( ''high confidence'' ). Overshooting 1.5°C will result in irreversible adverse impacts on certain ecosystems with low resilience, such as polar, mountain, and coastal ecosystems, impacted by ice-sheet melt, glacier melt, or by accelerating and higher committed sea level rise ( ''high confidence'' ). Overshoot increases the risks of severe impacts, such as increased wildfires, mass mortality of trees, drying of peatlands, thawing of permafrost and weakening natural land carbon sinks; such impacts could increase releases of GHGs making temperature reversal more challenging ( ''medium confidence'' ). { ''WGI SPM C.2, WGI SPM C.2.1, WGI SPM C.2.3; WGII SPM B.6, WGII SPM B.6.1, WGII SPM B.6.2; SR1.5 3.6'' }

The larger the overshoot, the more net negative CO 2 emissions needed to return to a given warming level ( ''high confidence'' ). Reducing global temperature by removing CO 2 would require net negative emissions of 220 GtCO 2 (best estimate, with a ''likely'' range of 160 to 370 GtCO 2 ) for every tenth of a degree ( ''medium confidence'' ). Modelled pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot reach median values of cumulative net negative emissions of 220 GtCO 2 by 2100, pathways that return warming to 1.5°C (&gt;50%) after high overshoot reach median values of 360 GtCO 2 ( ''high confidence'' ). '''[[#footnote-020|137]]''' More rapid reduction in CO 2 and non-CO 2 emissions, particularly methane, limits peak warming levels and reduces the requirement for net negative CO 2 emissions and CDR, thereby reducing feasibility and sustainability concerns, and social and environmental risks ( ''high confidence'' ). { ''WGI SPM D.1.1; WGIII SPM B.6.4, WGIII SPM C.2, WGIII SPM C.2.2, WGIII Table SPM.2'' }

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