Malte Meinshausen

1. Estimating warming levels from
emission pathways
08 NOVEMBER 2022
IPCC.CH
A/Prof. Malte Meinshausen
Thanks especially to: Zebedee R.J. Nicholls (Australia), Piers Forster (United Kingdom), Kyle Armour
(United States of America), Terje Berntsen (Norway), William Collins (United Kingdom), Christopher
Jones (United Kingdom), Jared Lewis (Australia/New Zealand), Jochem Marotzke (Germany), Sebastian
Milinski (Germany), Joeri Rogelj (United Kingdom/Belgium), Chris Smith (United Kingdom)
Making Sense of the IPCC Mitigation Scenarios
COP 27, Sharm El-Sheikh
Science for Climate Action Pavilion

2. WG1 climate system
assessment →
represented by climate
emulators
Comparison
between AR6
and SR1.5
1.5 °C and
other insights
WG3 scenario
classification

3. WG1 climate
system
assessment →
represented by
climate emulators
WG1 CCB7.1 Fig 1a

4. WG1 climate
system
assessment →
represented by
climate emulators
WG1 CCB7.1 Fig 1a

5. WG1 climate
system
assessment →
represented by
climate emulators
WG1 CCB7.1 Fig 1a

6. WG1 climate
system
assessment →
represented by
climate emulators
WG1 CCB7.1 Fig 1a

7. WG1 climate
system
assessment →
represented by
climate emulators
WG1 CCB7.1 Fig 1a

8. WG1 climate
system
assessment →
represented by
climate emulators
WG1 CCB7.1 Fig 1a

9. WG1 climate
system
assessment →
represented by
climate emulators
WG1 CCB7.1 Fig 1a

10. WG1 climate
system
assessment →
represented by
climate emulators
WG1 CCB7.1 Fig 1a

11. WG1 climate
system
assessment →
represented by
climate emulators
WG1 CCB7.1 Fig 1a

12. WG1 climate
system
assessment →
represented by
climate emulators
WG1 CCB7.1 Fig 1a

13. The climate emulators (i.e. calibrated reduced-
complexity models) represent historical warming
rather well.
→ What about the future?

14. WG1 CCB7.1 Fig 1cd

15. WG1 CCB7.1 Fig 1cd

16. WG1 CCB7.1 Fig 1cd

17. WG1 CCB7.1 Fig 1cd

18. WG1 CCB7.1 Fig 1cd

19. WG1 CCB7.1 Fig 1cd

20. WG1 CCB7.1 Fig 1cd
WG1 climate system assessment
taking into account equilibrium
climate sensitivity (ECS) and
transient climate response (TCR)
evidence

21. WG1 CCB7.1 Fig 1cd

22. WG1 CCB7.1 Fig 1cd

23. WG1 CCB7.1 Fig 1cd

24. WG1 CCB7.1 Fig 1cd

25. WG1 CCB7.1 Fig 1cd
WG1 climate emulators also
take into account carbon
cycle uncertainties

26. Detailed diagnostics of
climate emulator skills.
→ Successful vetting to
enable assessment of
>1000 WG3 scenarios
WG1 CCB7.1, Table 2

27. WG3
scenario
classification
WG3 Box SPM.1, Fig1

28. WG3 Box SPM.1, Fig1

29. WG3 Box SPM.1, Fig1
Lowest class of
scenarios around
1.5°C by 2030,
then decreasing
below 1.5°C in 2nd
half of the century

30. WG3 Box SPM.1, Fig1

31. WG3 Box SPM.1, Fig1

32. WG3 Box SPM.1, Fig1
Second lowest
scenario class has
higher 1.5°C overshoot,
then more negative
CO2 emissions to get
below 1.5°C before
2100
This evening:
separate IPCC
side event on
overshoot

33. WG3 Box SPM.1, Fig1
Climate system
uncertainties not
negligible. Even if
best-estimate
<1.5°C, we might
want to be prepared
for >2°C.

34. WG3 Box SPM.1, Fig1
Filled bar:
peak warming.
Open: 2100
warming.

35. WG3 Box SPM.1, Fig1
C3: Likely
(>67%)
below 2°C

36. WG3 Box SPM.1, Fig1

37. WG3 Box SPM.1, Fig1

38. WG3 Box SPM.1, Fig1
Between 2-3°C:
Range of most recent
NDC-up-to-2030-then-
continue or
“implemented policies”
analyses by IEA, UNEP
Gap or UNFCCC

39. WG3 Box SPM.1, Fig1

40. WG3 Box SPM.1, Fig1

41. WG3 Box SPM.1, Fig1

42. WG3 Box SPM.1, Fig1

43. WG3 Box SPM.1, Fig1

44. WG3 Box SPM.1, Fig1

45. WG3 Box SPM.1, Fig1

46. Close WG1-WG3 cooperation enables a consistent
scenario database and classification for further
analysis.
→ Putting the scenarios into context: A brief look at
GHG emissions.

47. WG3 SPM.4

48. Trend from
current
policies as
of end 2020
WG3 SPM.4

49. WG3 SPM.4

50. ~ NDCs
by 2030
WG3 SPM.4

51. 1.5°C with
no or
limited
overshoot
WG3 SPM.4

52. Likely
(>67%)
below 2°C
WG3 SPM.4

53. The steep
route to:
likely (>67%)
below 2°C
WG3 SPM.4

54. WG3 SPM.4

55. All “gap” analyses (IPCC, UNFCCC, UNEP Gap, …)
pretty similar:
Steep reductions BEFORE 2030 necessary to avoid
either:
● even steeper reductions after 2030 and still high
overshoot of 1.5°C or…
● warming in excess of 2°C

56. Has the warming assessment changed from IPCC
SR1.5 to AR6.
→ Yes, but offsetting effects kept classification very
similar.
(new assessment slightly higher peak and lower
long-term warming to be precise)

57. SR1.5
setup
Comparing
the ‘very low’
SSP1-1.9
scenario
Nicholls et al., 2022, GRL,https://doi.org/10.1029/2022GL099788

58. Comparing
the ‘very low’
SSP1-1.9
scenario
SR1.5
setup
AR6
setup
Nicholls et al., 2022, GRL,https://doi.org/10.1029/2022GL099788

59. SR1.5
setup
Comparing
the ‘very low’
SSP1-1.9
scenario
Nicholls et al., 2022, GRL,https://doi.org/10.1029/2022GL099788

60. AR6
setup
Comparing
the ‘very low’
SSP1-1.9
scenario
Nicholls et al., 2022, GRL,https://doi.org/10.1029/2022GL099788

61. Comparing
the SR1.5
1.5°C low
overshoot
scenarios
Nicholls et al., 2022, GRL,https://doi.org/10.1029/2022GL099788

62. Comparing
the SR1.5
1.5°C low
overshoot
scenarios
SR1.5
setup
Nicholls et al., 2022, GRL,https://doi.org/10.1029/2022GL099788

63. Comparing
the SR1.5
1.5°C low
overshoot
scenarios
AR6
setup
SR1.5
setup
Nicholls et al., 2022, GRL,https://doi.org/10.1029/2022GL099788

64. Has the warming assessment changed from IPCC
SR1.5 to AR6.
→ Yes, but offsetting effects kept classification very
similar.
(new assessment slightly high peak and lower long-
term warming to be precise)

65. @IPCC_CH
#IPCReport
For more information:
IPCC Secretariat: ipcc-sec@wmo.int
IPCC Press Office: ipcc-media@wmo.int
Visit ipcc.ch
@IPCC
@IPCC
linkedin.com/
company/ipcc
Thank you.
Malte Meinshausen
Professor at the University of Melbourne, Australia

66. Backup slides

69. Kikstra et al., 2022, EGUsphere, https://doi.org/10.5194/egusphere-2022-471

70. Kikstra et al., 2022, EGUsphere, https://doi.org/10.5194/egusphere-2022-471

71. IPCC AR6 WG3 Box 3.4, Figure 1

72. IPCC AR6 WG3 Box 3.4, Figure 2