Scientists: Only 10% Of The 1984-2017 Greenhouse Gas (Longwave) Forcing Was From CO2

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A late 2021 study finds water vapor and temperature changes accounted for 90% of the changes in clear-sky downwelling longwave or greenhouse effect forcing since the mid-1980s. CO2 forcing assumed a mere bit-player role.

The seminal Feldman et al. (2015) study concluded it takes 10 years and a 22 ppm increase in CO2 to account for just one-tenth of the total longwave or greenhouse effect forcing in recent (2000-2010) climate change trends. The remaining longwave forcing contribution is from water vapor and clouds.

Image Source: Berkeley Lab (press release) and Feldman et al., 2015

Other scientists (Clark et al., 2021) report CO2’s 10% contribution to greenhouse effect forcing can be applied to the period when CO2 rose from 344 to 405 ppm, or 1984 to 2017.

Image Source: Clark et al., 2021

Cloud-radiative forcing dominates in longwave

It should be noted that this proportionately small CO2 effect only applies in a hypothetical or non-real-world atmosphere that has no clouds in it.

In the real-world atmosphere “less than 10 percent of the sky is completely clear of clouds at any one time.”

And when clouds are present they dominate as the driver of greenhouse effect forcing. Quantitatively, the greenhouse effect of clouds is larger than a 100-fold increase in the CO2 concentration (~40,000 ppm).

Image Source: Ramanathan et al., 1989

So if CO2 has one-tenth of the total greenhouse effect forcing impact in an imaginary-world atmosphere that is perpetually cloud-free, and if the real-world atmosphere is cloud-free only about one-tenth of the time, we could conclude that CO2 has a 10% of 10% (1%) total impact in total greenhouse effect forcing.

Water vapor forcing dominates in cloud-free atmospheres

Other scientists have suggested the bit-player role for CO2 in clear-sky-only atmospheres is well less than the 10% outlined above.

In the real-world atmosphere water vapor concentrations can range from 35,000 to 40,000 ppm in the tropics to less than 500 ppm at the poles. Averaged over the globe, there are about 29 water vapor molecules for every 1 CO2 molecule in the atmosphere (Lightfoot and Mamer, 2017).

Image Source: Lightfoot and Mamer, 2017

But we also must consider “water molecules are 1.6 times more effective at warming than CO2 molecules” (Lightfoot and Mamer, 2014).

Image Source: Lightfoot and Mamer, 2014

So, putting it all together, the radiative forcing (RF) effect for CO2 molecules in a clear-sky-only atmosphere is “approximately 2.7% of the total RF of all the GHG [greenhouse gases]” (Lightfoot and Mamer, 2014).

How is it possible climate activists could get away with persuading the public CO2 is Earth’s temperature “control knob” all these years?

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5 responses to “Scientists: Only 105 Of The 1984-2017 Greenhouse Gas (Longwave) Forcing Was From CO2”

  1. Tom Anderson

    After all these years how can anyone believe “forcing” has any claim to reality? The alarmist conjecture is completely contrived smoke and mirrors, and “skepticism” made a Vichy-style armistice with it years ago.

  2. Yonason

    There are problems with a simplistic analysis of the effects of water vapor.

    It appears to yield negative feedback, not positive.

    That simple but elegant experiment, worthy (IMO) of Robert Wood, is supported by an in depth analysis of existing data bases.

    ”….Clive Best, who examined 5600 weather stations in the global CRUTEM4 temperature and humidity database, …[found]… that water vapor acts as a strong negative feedback rather than a positive feedback as alleged by the IPCC.”

    Caution – Theoretical deriving conditions subject to physical constraints.


    […] Fonte : notrickszone […]

  4. Wolfgang Richter

    What does this mean, that 10% of the global warming 1984-1917 is caused by CO2 and 90% by water vapor?
    Is this the water-vapor-amplification that is the base of the hypothesis of the issue, that the climate sensivity of CO2, measured in laboratory as about 1 °C is amplified by water vapor in the atmosphere so that the IPCC means the the “real” climate sensivity of CO2 is about 3 °C?
    Or is there no amplification and CO2 and water vapor ar acting separetly?

    1. E. Schaffer

      Well, all of this is a bit confused. “Back radiation” (BR) increases because temperatures increase. The direct effect of doubling CO2 on BR is relatively small, and irrelevant. Also BR is irrelevant and has nothing to do with the GHE.

      Regrettably a good of the papers presented above build on this fundamental misunderstanding. And they add a lot of mistakes on top of it.

      It is true however that CO2 only plays a minor role in global warming, but that is for different reasons as those named here.

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