SCI Climate categorization

Climate responses and emission trajectories are important characteristics of long-term global emissions scenarios. In light of the updated scenario ensemble and the resulting changes in warming outcomes, the SCI "Scientific working group on Emissions and Climate" developed a new warming categorization (Riahi et al., 2026). This framework builds on the warming categorizations used in SR1.5 and AR6, while improving the users’ understanding of the climatic implications of scenarios.

SCI climate categories with their warming criteria, end-of-century trends and corresponding IPCC AR6 categories
SCI Climate Category			Peak Warming(PW)	Climate and emissions trends at the end of the century			Corresponding IPCC AR6 category
Tier I	Tier II	Tier III	Peak Warming(PW)	Warming(EoCW)	GHG emissions	Temperature trend	Corresponding IPCC AR6 category
GW0	GW0Below 1.5°C without overshoot	GW0-IBelow 1.5°C without overshoot	PW₅₀ < 1.5°C	EoCW₅₀ < 1.5°C	Below net-zero	Decreasing	lower part of C1
GW0	GW0Below 1.5°C without overshoot	GW0-IIBelow 1.5°C without overshoot	PW₅₀ < 1.5°C	EoCW₅₀ < 1.5°C	Above zero		lower part of C1
GW1	GW1Below 1.6°C returning to 1.5°C	GW1-IBelow 1.5°C with limited overshoot	PW₅₀ < 1.6°C	EoCW₅₀ < 1.5°C	Below net-zero	Decreasing	C1
GW1	GW1Below 1.6°C returning to 1.5°C	GW1-IIBelow 1.5°C with limited overshoot	PW₅₀ < 1.6°C	EoCW₅₀ < 1.5°C	Above zero		C1
GW2	GW2aBelow 1.7°C returning to 1.5°C	GW2-ILikely returning to 1.5°C	PW₅₀ < 1.7°C	EoCW₆₇ < 1.5°C	Below net-zero	Decreasing	C2 [lower]
	GW2aBelow 1.7°C returning to 1.5°C	GW2-IIReturning to 1.5°C with 50% chance	PW₅₀ < 1.7°C	EoCW₅₀ < 1.5°C	Below net-zero	Decreasing	C2 [middle]
	GW2bBelow 1.7°C without returning to 1.5°C	GW2-IIIaTowards 1.5°C after 2100 with high overshoot	PW₅₀ < 1.7°C	EoCW₅₀ < 1.7°C	Below net-zero	Decreasing	C3 [lower]
		GW2-IIIbTowards 1.5°C after 2100 with high overshoot	PW₅₀ < 1.7°C	EoCW₅₀ < 1.7°C	Above zero	Decreasing	C3 [lower]
		GW2-IIIcTowards 1.5°C after 2100 with high overshoot	PW₅₀ < 1.7°C	EoCW₅₀ < 1.7°C	Above zero	Increasing	C3 [lower]
GW3	GW3aLikely below 2°C returning to 1.5°C	GW3-ILikely below 2°C returning to 1.5°C	PW₆₇ < 2°C	EoCW₅₀ < 1.5°C	Below net-zero	Decreasing	C2 [upper]
	GW3bLikely below 2°C without returning to 1.5°C	GW3-IIaLikely below 2°C	PW₆₇ < 2°C	EoCW₆₇ < 2°C	Below net-zero	Decreasing	C3
		GW3-IIbLikely below 2°C	PW₆₇ < 2°C	EoCW₆₇ < 2°C	Above zero	Decreasing	C3
		GW3-IIcBelow 2°C until 2100 with continuing warming	PW₆₇ < 2°C	EoCW₆₇ < 2°C	Above zero	Increasing	C3
GW4	GW4Below 2°C	GW4-IBelow 2°C with efforts to return warming to lower levels in 22nd century	PW₅₀ < 2°C	EoCW₅₀ < 1.7°C	Below net-zero	Decreasing	C4 [lower]
		GW4-IIaBelow 2°C	PW₅₀ < 2°C	EoCW₅₀ < 2°C	Below net-zero	Decreasing	C4 [middle]
		GW4-IIbBelow 2°C	PW₅₀ < 2°C	EoCW₅₀ < 2°C	Above zero	Decreasing	C4 [upper]
		GW4-IIcBelow 2°C by 2100 with continuing warming	PW₅₀ < 2°C	EoCW₅₀ < 2°C	Above zero	Increasing	C4
GW5	GW5Below 2.5°C	GW5-IBelow 2.5°C	PW₅₀ < 2.5°C	EoCW₅₀ < 2.5°C	Above zero	Decreasing	C5
GW5	GW5Below 2.5°C	GW5-IIBelow 2.5°C by 2100 with continuing warming	PW₅₀ < 2.5°C	EoCW₅₀ < 2.5°C	Above zero	Increasing	C5
GW6	GW6Below 3.0°C		PW₅₀ < 3°C	EoCW₅₀ < 3°C	Above zero		C6
GW7	GW7Below 3.5°C		PW₅₀ < 3.5°C	EoCW₅₀ < 3.5°C	Above zero		C7 [lower]
GW8	GW8Above 3.5°C		PW₅₀ ≥ 3.5°C		Above zero		C7 [upper] & C8

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