Summary for Policymakers 2023

Future Climate Change 3

B.1 Continued greenhouse gas emissions will lead to increasing global warming, with the best estimate

of reaching 1.5°C in the near term in considered scenarios and modelled pathways. Every increment of

global warming will intensify multiple and concurrent hazards (high confidence). Deep, rapid, and

sustained reductions in greenhouse gas emissions would lead to a discernible slowdown in global

warming within around two decades, and also to discernible changes in atmospheric composition within

a few years (high confidence). {Cross-Section Boxes 1 and 2, 3.1, 3.3, Table 3.1, Figure 3.1, 4.3} (Figure

SPM.2, Box SPM.1)

B.1.1 Global warming 28 will continue to increase in the near term (2021-2040) mainly due to increased 6

cumulative CO 2 emissions in nearly all considered scenarios and modelled pathways. In the near term, global 7

warming is more likely than not to reach 1.5°C even under the very low GHG emission scenario (SSP1-1.9) and 8

likely or very likely to exceed 1.5°C under higher emissions scenarios. In the considered scenarios and modelled 9

pathways, the best estimates of the time when the level of global warming of 1.5°C is reached lie in the near 10

term 29 . Global warming declines back to below 1.5°C by the end of the 21st century in some scenarios and 11

modelled pathways (see B.7). The assessed climate response to GHG emissions scenarios results in a best 12

estimate of warming for 2081–2100 that spans a range from 1.4°C for a very low GHG emissions scenario 13

(SSP1-1.9) to 2.7°C for an intermediate GHG emissions scenario (SSP2-4.5) and 4.4°C for a very high GHG 14

emissions scenario (SSP5-8.5) 30 , with narrower uncertainty ranges 31 than for corresponding scenarios in AR5. 15

{Cross-Section Boxes 1 and 2, 3.1.1, 3.3.4, Table 3.1, 4.3} (Box SPM.1)

B.5.2 For every 1000 GtCO 2 emitted by human activity, global surface temperature rises by 0.45°C (best 43

estimate, with a likely range from 0.27 to 0.63°C). The best estimates of the remaining carbon budgetsfrom the 44

39 Net zero GHG emissions defined by the 100-year global warming potential. See footnote 9.

Approved Summary for Policymakers IPCC AR6 SYR

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beginning of 2020 are 500 GtCO 2 for a 50% likelihood of limiting global warming to 1.5°C and 1150 GtCO 2 1

for a 67% likelihood of limiting warming to 2°C 40 . The stronger the reductions in non-CO 2 emissions the lower 2

the resulting temperatures are for a given remaining carbon budget or the larger remaining carbon budget for 3

the same level of temperature change 41 . {3.3.1} 4

B.5.3 If the annual CO 2 emissions between 2020–2030 stayed, on average, at the same level as 2019, the 6

resulting cumulative emissions would almost exhaust the remaining carbon budget for 1.5°C (50%), and deplete 7

more than a third of the remaining carbon budget for 2°C (67%). Estimates of future CO 2 emissions from 8

existing fossil fuel infrastructures without additional abatement 42 already exceed the remaining carbon budget 9

for limiting warming to 1.5°C (50%) (high confidence). Projected cumulative future CO 2 emissions over the 10

lifetime of existing and planned fossil fuel infrastructure, if historical operating patterns are maintained and 11

without additional abatement 43 , are approximately equal to the remaining carbon budget for limiting warming 12

to 2°C with a likelihood of 83% 44 (high confidence). {2.3.1, 3.3.1, Figure 3.5}

B.5.4 Based on central estimates only, historical cumulative net CO 2 emissions between 1850 and 2019 amount 15

to about four-fifths 45 of the total carbon budget for a 50% probability of limiting global warming to 1.5°C 16

(central estimate about 2900 GtCO 2 ), and to about two thirds 46 of the total carbon budget for a 67% probability 17

to limit global warming to 2°C (central estimate about 3550 GtCO 2 ). {3.3.1, Figure 3.5}