Editing IPCC:AR6/SR15/Chapter-2 (section)

==== Classification of pathways that this chapter draws upon, along with the number of available pathways in each class ====

The definition of each class is based on probabilities derived from the MAGICC model in a setup identical to AR5 WGIII (Clarke et al., 2014) <sup>[[#fn:r14|14]]</sup> , as detailed in Supplementary Material  2.SM.1.4.

{| class="wikitable"
|-
! Pathway Group
! Pathway Class
! Pathway Selection Criteria and Description
! Number of Scenarios
|-
| rowspan="3"| 1.5°C or<br />
1.5°C-consistent**
| Below-1.5°C
| Pathways limiting peak warming to below 1.5°C during the entire 21st century with 50–66% likelihood*
| 9
| rowspan="3"| 90
|-
| 1.5°C-low-OS
| Pathways limiting median warming to below 1.5°C in 2100 and with a 50–67% probability of temporarily overshooting that level earlier, generally implying less than 0.1°C higher peak warming than Below-1.5°C pathways
| 44
|-
| 1.5°C-high-OS
| Pathways limiting median warming to below 1.5°C in 2100 and with a greater than 67% probability of temporarily overshooting that level earlier, generally implying 0.1–0.4°C higher peak warming than Below-1.5°C pathways
| 37
|-
| rowspan="2"| 2°C or<br />
2°C-consistent
| Lower-2°C
| Pathways limiting peak warming to below 2°C during the entire 21st century with greater than 66% likelihood
| 74
| rowspan="2"| 132
|-
| Higher-2°C
| Pathways assessed to keep peak warming to below 2°C during the entire 21st century with 50–66% likelihood
| 58
|}

\* No pathways were available that achieve a greater than 66% probability of limiting warming below 1.5°C during the entire 21st century based on the MAGICC model projections.

\** This chapter uses the term 1.5°C-consistent pathways to refer to pathways with no overshoot, with limited (low) overshoot, and with high overshoot. However, the Summary for Policymakers focusses on pathways with no or limited (low) overshoot.

In addition to the characteristics of the above-mentioned classes, four illustrative pathway archetypes have been selected and are used throughout this chapter to highlight specific features of and variations across 1.5°C pathways. These are chosen in particular to illustrate the spectrum of CO <sub>2</sub> emissions reduction patterns consistent with 1.5°C, ranging from very rapid and deep near-term decreases, facilitated by efficiency and demand-side measures that lead to limited CDR requirements, to relatively slower but still rapid emissions reductions that lead to a temperature overshoot and necessitate large CDR deployment later in the century (Section 2.3).

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