Editing IPCC:AR6/WGIII/Chapter-3 (section)

=== FAQ 3.2 | How can net zero emissions be achieved and what are the implications of net zero emissions for the climate? ===

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Halting global warming in the long term requires, at a minimum, that no additional CO 2 emissions from human activities are added to the atmosphere (i.e., CO 2 emissions must reach ‘net’ zero). Given that CO 2 emissions constitute the dominant human influence on global climate, global net zero CO 2 emissions are a prerequisite for stabilising warming at any level. However, CO 2 is not the only greenhouse gas that contributes to global warming and reducing emissions of other greenhouse gases (GHGs) alongside CO 2 towards net zero emissions of all GHGs would lower the level at which global temperature would peak. The temperature implications of net zero GHG emissions depend on the bundle of gases that is being considered, and the emissions metric used to calculate aggregated GHG emissions and removals. If reached and sustained, global net zero GHG emissions using the 100-year Global Warming Potential (GWP-100) will lead to gradually declining global temperature.

Not all emissions can be avoided. Achieving net zero CO 2 emissions globally therefore requires deep emissions cuts across all sectors and regions, along with active removal of CO 2 from the atmosphere to balance remaining emissions that may be too difficult, too costly, or impossible to abate at that time. Achieving global net zero GHG emissions would require, in addition, deep reductions of non-CO 2 emissions and additional CO 2 removals to balance remaining non-CO 2 emissions.

Not all regions and sectors must reach net zero CO 2 or GHG emissions individually to achieve global net zero CO 2 or GHG emissions, respectively; instead, positive emissions in one sector or region can be compensated by net negative emissions from another sector or region. The time each sector or region reaches net zero CO 2 or GHG emissions depends on the mitigation options available, the cost of those options, and the policies implemented (including any consideration of equity or fairness). Most modelled pathways that ''likely'' limit warming to 2°C (&gt;67%) above pre-industrial levels and below use land-based CO 2 removal such as afforestation/reforestation and BECCS to achieve net zero CO 2 and net zero GHG emissions even while some CO 2 and non-CO 2 emissions continue to occur. Pathways with more demand-side interventions that limit the amount of energy we use, or where the diet that we consume is changed, can achieve net zero CO 2 , or net zero GHG emissions with less carbon dioxide removal (CDR). All available studies require at least some kind of carbon dioxide removal to reach net zero; that is, there are no studies where absolute zero GHG or even CO 2 emissions are reached by deep emissions reductions alone.

Total GHG emissions are greater than emissions of CO 2 only; reaching net zero CO 2 emissions therefore occurs earlier, by up to several decades, than net zero GHG emissions in all modelled pathways. In most modelled pathways that ''likely'' limit warming to 2°C (&gt;67%) above pre-industrial levels and below in the most cost-effective way, the agriculture, forestry and other land-use (AFOLU) and energy supply sectors reach net zero CO 2 emissions several decades earlier than other sectors; however, many pathways show much reduced, but still positive, net GHG emissions in the AFOLU sector in 2100.

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