I am trying to understand how athmospheric scientists are quantifying effective radiative forcing of different aviation-related warming/cooling effects as a function of total emissions over time.

For instance, a recent publication (Penner et al., 2018, https://doi.org/10.1029/2018JD029204) mentions, that:

Our best estimate for the forcing of aircraft soot in this model is -0.2 ± 0.06 W/m²;

I read the paper, but could not find over what time period this level of absolute warming (mW/m²) is supposed to occur.

On the other hand, the well-known figures by Lee et al. (https://doi.org/10.1016/j.atmosenv.2020.117834, latest version from 2021) always provide the time horizon. In this example, the effective radiative forcing level from different aviation-related effects are all calculated for the time period 1940-2018.

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Am I missing something in the publication by Penner et al.? Is it convention in atmospheric science to implicitly assume some time period (industrial revolution until the present day?)?


1 Answer 1


Soot is like water vapour in that its has a very short atmospheric lifetime, so its forcing is not cumulative that way CO2 is. There is no need to specify a time period for the contribution from soot.

The lifetime of atmospheric CO2 is hundreds of years, so to estimate the current forcing from aviation CO2, you need to know how much CO2 has ever been emitted by aviation. The table in Lee specifies the time period because it includes contributions from CO2 and other long-lived greenhouse gases such as nitrous oxides. (I am not sure why 1940 is the cutoff, but earlier contribution from aviation must be negligible.)

The atmospheric lifetime of soot is days to weeks, so the current forcing from aviation soot only depends on the current production rate of soot, not the production over a long historical period. The forcing estimated by Penner is presumably the amount that would disappear in a few weeks if all aviation was grounded. As the OP notes, it would still have been best if they had specified the base year or level of air traffic.

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    $\begingroup$ Excellent point - although even in this case it would be helpful if the publication mentioned the base year (or the level of air traffic) associated with the ERF? $\endgroup$ Oct 18, 2023 at 14:48
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    $\begingroup$ @Wasserwaage I agree, they should have specified the base year or level of air traffic. It may be buried in the references somewhere, but it is certainly not obvious. $\endgroup$ Oct 18, 2023 at 15:15

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