This is in the discussion on the radiative forcing implications: *The Twomey effect estimates are much better constrained for the calculations using Re, but those using Acld show consistent results. The IMO 2020 regulations led to an ~2 W m-2 IRFACI within the shipping corridor during austral spring and an ~0.5 W m-2 IRFACI in the annual mean. Taking the ~70% decline in IRFACI from the austral spring revalues an upper bound and applying it to the -0.1 to -0.6 W m-2 range of forcing due to shipping emissions from global models (Capaldo et al., 1999; Lauer et al., 2007; Peters et al., 2013; Righi et al., 2011; Sofiev et al., 2018), global forcing values of O(0.1 W m-2) and up to +0.4W m-2 due to the IMO 2020 regulations are plausible.*
(Re = effective radius, Acld = top of atmosphere albedo with clouds present, IRFACI = instantaneous radiative forcing from aerosol-cloud interactions) So it sounds like within the shipping corridor itself, it's putatively -2W/m2 instantaneous forcing when ship tracks are present. However, the probability density plot for the estimated Twomey effect in Figure 5 shows quite a spread, particularly for Austral spring. That, along with the uncertainty range for global forcing due to shipping emissions used to extrapolate to the global effect, it sounds like there's a fair bit of uncertainty on the ~1W/m2 estimate. On Friday, 26 May 2023 at 12:22:30 am UTC+10 Stephen Salter wrote: > Hi All > > What a useful paper! > > I am a bit surprised that the instantaneous change is only 1 watt per > square metre. The 20 bar grey scale at the bottom of the image below shows > that we need at least three bars, 15% change, to detect the direction of a > contrast gradient. Ship track images often show much more than this. Is it > because somebody has tweaked the gamma range or that we do not see ship > tracks that often? Maybe I misunderstand instantaneous. > > > > > > > > Stephen > > > > *From:* [email protected] <[email protected]> *On > Behalf Of *Geoengineering News > *Sent:* 25 May 2023 13:37 > *To:* [email protected] > *Subject:* [geo] Detection of large-scale cloud microphysical changes and > evidence for decreasing cloud brightness within a major shipping corridor > after implementation of the International Maritime Organization 2020 fuel > sulfur regulations (Preprint) > > > > *This email was sent to you by someone outside the University.* > > You should only click on links or attachments if you are certain that the > email is genuine and the content is safe. > > https://egusphere.copernicus.org/preprints/2023/egusphere-2023-971/ > > > > *Author* > > Michael Steven Diamond > > Received: 11 May 2023 – *Discussion started: 22 May 2023* > > *Abstract.* New regulations from the International Maritime Organization > (IMO) limiting sulfur emissions from the shipping industry are expected to > have large benefits in terms of public health but come with an undesired > side effect: an acceleration of global warming as the climate-cooling > effects of ship pollution on marine clouds is diminished. Previous work has > found a substantial decrease in the detection of ship tracks in clouds > after the IMO 2020 regulations went into effect but changes in large-scale > cloud properties have been more equivocal. Using a statistical technique > that estimates counterfactual fields of what large-scale cloud and > radiative properties within an isolated shipping corridor in the > southeastern Atlantic would have been in the absence of shipping, we > confidently detect a reduction in the magnitude of cloud droplet effective > radius decreases within the shipping corridor and find evidence for a > reduction in the magnitude of cloud brightening as well. The instantaneous > radiative forcing due to aerosol–cloud interactions from the IMO 2020 > regulations is estimated as *O*(1 W m-2) within the shipping corridor, > lending credence to global estimates of *O*(0.1 W m-2). In addition to > their geophysical significance, our results also provide independent > evidence for general compliance with the IMO 2020 regulations. > > *How to cite. *Diamond, M. S.: Detection of large-scale cloud > microphysical changes and evidence for decreasing cloud brightness within a > major shipping corridor after implementation of the International Maritime > Organization 2020 fuel sulfur regulations, EGUsphere [preprint], > https://doi.org/10.5194/egusphere-2023-971, 2023. > > > > *Source: EGU Sphere* > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/geoengineering/CAHJsh9-zkOcRCXOqTnNmHeXk06asVwg-K7C7p%2BDDr%2B%3D6xEhuRw%40mail.gmail.com > > <https://groups.google.com/d/msgid/geoengineering/CAHJsh9-zkOcRCXOqTnNmHeXk06asVwg-K7C7p%2BDDr%2B%3D6xEhuRw%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > The University of Edinburgh is a charitable body, registered in Scotland, > with registration number SC005336. Is e buidheann carthannais a th’ ann an > Oilthigh Dhùn Èideann, clàraichte an Alba, àireamh clàraidh SC005336. > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/14472647-2249-4d13-aa52-12287e60fb55n%40googlegroups.com.
