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

=== Climate Response to Emissions Reduction, Carbon Dioxide Removal and Solar Radiation Modification ===

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'''If strong mitigation is applied from 2020 onward as reflected in SSP1-1.9, its effect on 20-year trends in GSAT would''' ''likely'' '''emerge during the near term (2021–2040), measured against an assumed non-mitigation scenario such as S''' '''SP3-7.''' '''0 and SSP5-8.5. However, the response of many other climate quantities to mitigation would be largely masked by internal variability during the near term, especially on the regional scale''' ( ''high confidence'' ''').''' The mitigation benefits for these quantities would emerge only later during the 21st century ( ''high confidence'' ). During the near term, a small fraction of the surface can show cooling under all scenarios assessed here, so near-term cooling at any given location is fully consistent with GSAT increase ( ''high confidence'' ). Events of reduced and increased GSAT trends at decadal time scales will continue to occur in the 21st century but will not affect the centennial warming ( ''very high confidence'' ). {4.6.3, Cross-Chapter Box 3.1}

'''Because of the near-linear relationship between cumulative carbon emissions and GSAT change, the cooling or avoided warming from carbon dioxide removal (CDR) is proportional to the cumulative amount of CO''' <sub>2</sub> '''removed by CDR''' ( ''high confidence'' ''').''' The climate system response to net negative CO <sub>2</sub> emissions is expected to be delayed by years to centuries. Net negative CO <sub>2</sub> emissions due to CDR will not reverse some climate change, such as sea level rise, at least for several centuries ( ''high confidenc'' e). The climate effect of a sudden and sustained CDR termination would depend on the amount of CDR-induced cooling prior to termination and the rate of background CO <sub>2</sub> emissions at the time of termination ( ''high confidence'' ). {4.6.3, 5.5, 5.6}

'''Solar radiation modification (SRM) could offset some of the effects of anthropogenic warming on global and regional climate, but there would be substantial residual and overcompensating climate change at the regional scale and seasonal time scale''' ( ''high confidence'' '''), and''' '''there is''' ''low confidence'' '''in our understanding of the climate response to SRM, specifically at the regional scale.''' Since AR5, understanding of the global and regional climate response to SRM has improved, due to modelling work with more sophisticated treatment of aerosol-based SRM options and stratospheric processes. Improved modelling suggests that multiple climate goals could be met simultaneously. A sudden and sustained termination of SRM in a high-emissions scenario such as SSP5-8.5 would cause a rapid climate change ( ''high confidence'' ). However, a gradual phase-out of SRM combined with emissions reductions and CDR would ''more'' ''likely than not'' avoid larger rates of warming '''.''' {4.6.3}

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