Table 2 GWPs for methane in IPCC assessment reports (ARs)

AR1

10

63

21

Determined GWP of CH₄ by including indirect effects on stratospheric water vapor, CO₂ and tropospheric ozone

SAR

12

56

21

Updated estimates of atmospheric lifetimes, molecular RF factors, and representation of the carbon cycle

TAR

12

62

23

Decreased RF per kg of CO₂ by 12%

AR4

12

72

25

Included climate-carbon feedbacks for calculating AGWP of CO₂ based on Plattner et al. (2008). Increased the direct RF of CH₄ by 25% (due to tropospheric ozone) and 15% (due to stratospheric H₂O vapor)

AR5

12.4

84 (85)^a

28 (30)

Included climate-carbon feedbacks for calculating the AGWP of CO₂ based on Joos et al. (2013)

86 (87)

34 (36)

Included climate-carbon feedbacks for calculating the AGWPs of both CO₂ and CH₄