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

==== 3.3.2 Net Zero Emissions: Timing and Implications ====

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'''From a physical science perspective, limiting human-caused global warming to a specific level requires limiting cumulative CO''' '''2''' '''emissions, reaching net zero or net negative CO''' '''2''' '''emissions, along with strong reductions of other GHG emissions (see Cross-Section Box.1). Global modelled pathways that reach and sustain net zero GHG emissions are projected to result in a gradual decline in surface temperature (''' '''''high confidence).''''' Reaching net zero GHG emissions primarily requires deep reductions in CO 2 , methane, and other GHG emissions, and implies net negative CO 2 emissions. '''[[#footnote-023|134]]''' Carbon dioxide removal (CDR) will be necessary to achieve net negative CO 2 emissions '''[[#footnote-022|135]]''' . Achieving global net zero CO 2 emissions, with remaining anthropogenic CO 2 emissions balanced by durably stored CO 2 from anthropogenic removal, is a requirement to stabilise CO 2 -induced global surface temperature increase (see 3.3.3). ( ''high confidence'' ). This is different from achieving net zero GHG emissions, where metric-weighted anthropogenic GHG emissions (see Cross-Section Box.1) equal CO 2 removal ( ''high confidence'' ). Emissions pathways that reach and sustain net zero GHG emissions defined by the 100-year global warming potential imply net negative CO 2 emissions and are projected to result in a gradual decline in surface temperature after an earlier peak ( ''high confidence'' ). While reaching net zero CO 2 or net zero GHG emissions requires deep and rapid reductions in gross emissions, the deployment of CDR to counterbalance hard-to-abate residual emissions (e.g., some emissions from agriculture, aviation, shipping, and industrial processes) is unavoidable ( ''high confidence'' ). { ''WGI SPM D.1,'' . ''WGI SPM D.1.1, WGI SPM D.1.8; WGIII SPM C.2, WGIII SPM C.3, WGIII SPM C.11, WGIII Box TS.6; SR1.5 SPM A.2.2'' }

'''In modelled pathways, the timing of net zero CO '''2''' emissions, followed by net zero GHG emissions, depends on several variables, including the desired climate outcome, the mitigation strategy and the gases covered''' '''''(''''' '''''high confidence).''''' Global net zero CO 2 emissions are reached in the early 2050s in pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot, and around the early 2070s in pathways that limit warming to 2°C (&gt;67%). While non-CO 2 GHG emissions are strongly reduced in all pathways that limit warming to 2°C (&gt;67%) or lower, residual emissions of CH 4 and N 2 O and F-gases of about 8 [5–11] GtCO 2 -eq yr ''-1'' remain at the time of net zero GHG, counterbalanced by net negative CO 2 emissions. As a result, net zero CO 2 would be reached before net zero GHGs. ( ''high confidence'' ). { ''WGIII SPM C.2, WGIII SPM C.2.3, WGIII SPM C.2.4, WGIII Table SPM.2, WGIII 3.3'' } (Figure 3.6)

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'''Figure 3.6: Total GHG, CO''' '''2''' '''and CH''' '''4''' '''emissions and timing of reaching net zero in different''' '''mitigation''' '''pathways. Top row:''' GHG, CO 2 and CH 4 emissions over time (in GtCO 2 eq) with historical emissions, projected emissions in line with policies implemented until the end of 2020 (grey), and pathways consistent with temperature goals in colour (blue, purple, and brown, respectively). '''Panel (a) (left)''' shows pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot (C1) and '''Panel (b) (right)''' shows pathways that limit warming to 2°C (&gt;67%) (C3). '''Bottom row: Panel (c)''' shows median (vertical line), ''likely'' (bar) and ''very likely'' (thin lines) timing of reaching net zero GHG and CO 2 emissions for global modelled pathways that limit warming to 1.5°C (&gt;50%) with no or limited overshoot (C1) (left) or 2°C (&gt;67%) (C3) (right). { ''WGIII Figure SPM.5'' }

[https://www.ipcc.ch/figures/figure-3-6 ]

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