The formula for estimating radiative forcing (RF or ΔF) from a change in atmospheric CO2 concentration is usually given as:
C/C₀ is the ratio of new to old CO2 concentrations
Myhre 1998 and the IPCC
(TAR & later) estimate:
𝞪 = 5.35 ±0.58
(which is
3.7 ±0.4 W/m² per doubling of CO2)
Happer 2013[2]
(and 2015) reports calculating, based on corrected modeling of
CO2 lineshapes, that that's ≈40% too high, which makes:
𝞪 ≈ 3.8 ±0.5 (which is 2.6 ±0.5 W/m² per doubling)
van Wijngaarden & Happer 2021 (preprint) (see also 2020
& 2022)
report calculating ERF at the mesopause (similar to TOA) from doubling CO2 to be:
𝞪 = 4.28 (which is 2.97 W/m² per doubling)
Prof. Joshua Halpern reports:
𝞪 = 4.35 (https://twitter.com/EthonRaptor/status/1254176110507626499)
Feldman et al 2015 measured downwelling longwave IR “back radiation” from CO2,
at ground level, under clear sky conditions, for a decade. They reported that a 22 ppmv (= +5.946%)
increase in atmospheric CO2 level (+8.333% forcing) resulted in a 0.2 ±0.06 W/m² increase in downwelling LW IR from CO2,
which is +2.40 ±0.72 W/m² per CO2 doubling.
𝞪 ≈ 4.47 ±1.34 (which is 3.10 ±0.93 W/m² per doubling)
Rentsch 2020 (draft), analyzed AIRS satellite spectroscopy, and found that under nighttime, cloud-clear conditions, a 37 ppmv CO2 increase
caused +0.358 ±0.067 W/m² radiative forcing increase at TOA, which is:
𝞪 = 3.79 ±0.71 (which is 2.62 ±0.49 W/m² per doubling)
NEW: Kramer, RJ et al. 2021. Observational evidence of increasing global radiative forcing. Geophysical Research Letters, 48, e2020GL091585. doi:10.1029/2020GL091585. (See discussion.)
For full details see: https://sealevel.info/Radiative_Forcing.html
For effect on temperatures see: https://sealevel.info/sensitivity.html
For similar calculations for CH4 see: https://sealevel.info/methane.html
For graphs of atmospheric CO2 concentration see: https://sealevel.info/co2.html
For CO2 emissions data see: https://sealevel.info/carbon/
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