# Talk:Global dimming

I can't find any publication by Ohmura in 1989, but he has four in 1990:

Ohmura, A., 1990: Reevaluation and monitoring of the global energy balance.  Sanderson, M. (Ed.): UNESCO Source Book in Climatology, 35-42.
Chen, J. and Ohmura, A., 1990: On the influence of Alpine glaciers on runoff. Lang, H. and Musy, A. (Eds.): Hydrology in Mountainous Regions I, IAHS Publ., 193, 117-125.
Chen, J. and Ohmura, A., 1990: Estimation of Alpine glacier water resources and their change since 1870s. Lang, H. and Musy, A. (Eds): Hydrology in Mountainous Regions I, IAHS Publ., 193, 127-135.
Enomoto, J. and Ohmura, A., 1990: The influence of atmospheric half-year cycle on the sea ice extent in the Antarctic. J.Geophys.Res, 95, 9497-9511.
I'd guess that the first one is the most likely to be the relevant paper. -- John Fader 20:09, 15 Jan 2005 (UTC)

(William M. Connolley 21:02, 15 Jan 2005 (UTC)) Thanks. Now all we need is for someone to check the UNESCO book... incidentally, there is something by Ohmura in 1989 (O, Gilgen and Wild, but it looks like a tech rep not in a journal and may well be in German):  Ohmura, A., H. Gilgen, and M. Wild (1989), Global Energy Balance Archive GEBA, World Climate Program—Water Project A7, Report 1: Introduction, Zuercher Geografische Schriften Nr. 34, Verlag der Fach-vereine, Zuerich, 62 pp.

(Ferdinand Engelbeen 20:20, 16 Jan 2005 (UTC)) 
The theory behind the Horizon program, that more sunlight is reflected due to (sulphate) aerosols is at odds with measurements from space.
For the (sub)tropics, in the period 1985-2001 the amount of sunlight reflected by clouds reduced with ~2 W/m2 in the tropics (20N-20S). (see: http://www.atmos.ucla.edu/csrl/publications/pub_exchange/Wielicki_et_al_2002.pdf, confirmed for the 30N-30S (sub)tropics in http://pubs.giss.nasa.gov/docs/2002/2002_ChenCarlsonD.pdf) 
In the 1985-1994 period, there was a loss of cloud cover, both in the tropics and subtropics (and even up to 60N-60S) of 0.33% and 1.7% respectively.
If there is global dimming at the surface and no more reflection, the only explanation possible is that more sunlight is retained in the atmosphere itself. Which is possible with (dark brown and black) soot particulate. 
If soot particulate is to blame, then a reduction of it would have a cooling effect, not a warming effect.
Another hint is the amount of reflected sunlight from earth on the moon ("earthshine"), which parallels the "global dimming" trend, while it should have an opposite trend, at: http://www.bbso.njit.edu/science_may28.html (main page at http://www.bbso.njit.edu/ )

(William M. Connolley 09:23, 27 Apr 2005 (UTC)) Somewhat in a hurry, I removed "This cooling effect may have led scientists to underestimate the effect of greenhouse gases on global warming." from the intro. I'm not really sure it *is* a cooling effect. Certainly a 5% reduction in solar would produce huge cooling, which would be obvious; since that isn't there, the (observed) solar reduction at the sfc is balanced by other effects - the same solar abs at higher levels; or diffuse.

I wonder if that might be better as more readable? Chidgk1 (talk) 07:39, 17 December 2023 (UTC)

How about now? InformationToKnowledge (talk) 11:40, 17 December 2023 (UTC)

I see this article is currently undergoing a GA review. That's great. I came to this article as I am currently looking at improving radiative forcing. I wonder if the term "global dimming" is just an "easier to understand term" for something that is already covered in some other articles as well. Namely in the article on particulates. From the main climate change article I get sent to Particulates#Climate effects and now I am wondering if that section doesn't already cover the same content as what is at global dimming? If not then how do the two articles interact, is one the parent article of the other? Might be worth looking at so ensure we don't repeat the same content in two places or at least to ensure that the two articles interlink well. 
My suggestion would be to include in the global dimming article a bit more on the political/historical aspects, i.e. how the global dimming phenomenon was used by climate change deniers/skeptics for a long time (although I now see that the climate change denial article doesn't even mention global dimming once). But see e.g. History of climate change science#Discredited theories and reconciled apparent discrepancies. The article Scientific consensus on climate change mentions "global dimming" just once in the section about the 1970s. So I guess this is about interlinking this article with the other ones. EMsmile (talk) 12:30, 16 January 2024 (UTC)

Yes, there have been issues with article overlap regarding this general subject for a very long time. I noted exactly that on the WikiProject talk page (now archived) when I started work on this set of articles from about March to May last year. One reason why there is overlap in the Particulates article is because  pulled much of the salvageable content from very low-quality Stratospheric sulfur aerosols there (in addition to this article and solar geoengineering) before merging that into stratospheric aerosol injection. SAI now has the most daily pageviews of the three, which is a little unfortunate, since it was the one I worked on the least - in part because it used to be well behind this article and SG back then.
Anyway, Particulates was never meant to be a long-term destination for that information. Back then, it was an overlong article that struggled with proportionality in section size, layout, etc. and had an lots of overlap with air pollution (which itself suffers from many of the same issues) - and it is basically the same now, still. I believe you suggested making that article about all forms of particulate matter, including in water, and that might work if the article is covering types of particulate matter and the details about health effects, etc. are moved to Air pollution - but that would be a  really complex merge, painful cuts may need to be made to combine two already large articles, and the merge discussion there might make the climate apocalypse one (recently closed with no consensus) look easy by comparison.
I think you had also suggested sometime last year that the climate-related material in Particulates should really be in Aerosol, and strictly speaking, that would be absolutely right, as the IPCC and effectively all the research papers use the term aerosol in the climate context, while particulate is generally limited to health context. The issue is that the Aerosol article is itself an unholy mess, with relatively few paragraphs and only a couple dozen unique references (some of which are cited 10-20 times as separate references - usually the ones that are from 1990s and 1980s), but with lots of protracted equations. (Somehow, it still consistently gets >500 daily views month after month, suggesting readers don't mind?) It also has relatively little detail on climate but some paragraphs that go into health effects - these should probably be exchanged with particulates' climate effects paragraphs before anything else is done.
From the main climate change article I get sent to Particulates#Climate effects and now I am wondering if that section doesn't already cover the same content as what is at global dimming?
Firstly, I would say that while Particulates#Climate effects is not as bad as Aerosol is right now, everything it says before the "Sulfate" heading is also not great, with too many over-long sentences and citations from 2000s like AR4. Hopefully, we can be fixed after we move it to aerosols, but it might take some time. For now, I have just removed your "See also" link heading there for that reason. That and because the Aerosols section in Climate change (your other "See also" link) is effectively just a very short summary of that exact section, so linking it is completely counterproductive. You have done the same thing earlier on Greenland ice sheet - linking to the section in sea level rise which only provides a brief overview of that exact article. Please try to be more careful with that next time!
Secondly, that section is only about the impact on temperatures, and does not really say anything about either, well, the visual dimming itself, or, more importantly, the hydrological impact - which had been credibly linked to an major famine, as this article now describes. In theory, a revised version of Aerosol might be able to fit all that information, but I suspect it would look very awkward and bloated and worse than what we have now.
i.e. how the global dimming phenomenon was used by climate change deniers/skeptics for a long time
The thing is, I am not sure it was really used in that way in any meaningful sense. One of the references that's been here for a very long time is a 2003 article from The Guardian, which claims that it was largely obscure as recently as 20 years ago. (Though, since even the 1990 IPCC report talked about it at length, I suspect a lot of that is The Guardian's typical exaggeration -  that article did not age well at all in many respects.) As stated in scientific consensus on climate change, the scientists who disagreed with the consensus also seemed to incorrectly attribute the cooling from dimming to volcanoes - at least in that one survey I found.
If there is one article where there really is an overlap in that regard, it's global cooling - but that article also looks like it could benefit from substantial clean-up, with a lot of poorly structured direct quotes and other issues like that. Still, two or three references look usable, so I'll have to think about it. InformationToKnowledge (talk) 14:17, 16 January 2024 (UTC)
Just wondering: if there is overlap with global cooling shouldn't we at least mention global cooling once or twice? For now, I have added it to the See also section. Even if the article is not great, I think it does deserve a mention as it's certainly related, isn't it? EMsmile (talk) 22:54, 16 April 2024 (UTC)

Hi InformationToKnowledge: you put this graph back in which I have just removed (see on the right): 
The reason why I had removed it was because I don't think it was specific enough for this article. Also the caption looked out of date for me and without a reference?
On the article radiative forcing I have given it a different caption and the exact source, see on the right the second graph.

Could we at least agree to improve the caption with a source here as well? Making it clear and understandable to lay persons?
The same graph appears in quite a few articles by the way, and I think in each case the caption should be looked at (and adapted if necessary) and the source given, with page number:

Attribution of recent climate change
Cloud feedback
Sulfur dioxide
Global dimming
Radiative forcing
Climate change
Carbon dioxide in Earth's atmosphere
Greenhouse gas
Atmospheric methane
Gas venting
P.S. I know that the source can be found by readers when they click on the image but I think it's good practice to add the source also to the caption itself, just to be sure.

 EMsmile (talk) 13:45, 16 January 2024 (UTC)
I mean, that graph is used on a lot of articles because it really is very useful. It might need to be removed from some of those, but certainly not this one. As for the source, yes, the first sentence should be sourced to SPM, while references 76-78 in the article all make the case that there is unfortunately still a lot of uncertainty about the exact amount of cooling, which is why that large error bar is needed (It is not "outdated" at all!) I simply overlooked adding one or all of them to the caption that time. InformationToKnowledge (talk) 14:26, 16 January 2024 (UTC)
OK, but this wording in the caption is unclear to me: "including the cooling provided by sulfate aerosols and the dimming they cause". Is cooling and dimming now two different things here? Also this sentence could be made clearer by adding the words in bold: "The large error bar for the contribution of sulphur dioxide in particular shows that there are still substantial unresolved uncertainties." And what are "substantial unresolved uncertainties", surely there could be simpler wording for that? Is that source on page 7 saying it in those exact words? Does that uncertainty get explained in the main text? I only see it mentioned twice in the Wikipedia article text. Perhaps it deserves a separate sub-heading?  EMsmile (talk) 15:34, 16 January 2024 (UTC)
I still find the caption for that bar chart image rather unclear and layperson-unfriendly. Marked in bold where I stumble over the wording The extent to which physical factors in the atmosphere or on land affect climate change. This includes sulfur dioxide, which reacts to form a variety of sunlight-reflecting sulfates. The large error bar shows that there are still substantial unresolved uncertainties about the strength of cooling caused by their dimming. EMsmile (talk) 22:43, 16 April 2024 (UTC)
OK, so here's my proposal for a caption that is easier to understand: This chart shows how much various physical factors affect climate change. For example, sulfur dioxide causes cooling because it reacts to form a variety of sunlight-reflecting sulfates. Its large error bar shows that there is a lot of uncertainty regarding the strength of cooling caused by sulphur dioxide in the atmosphere. EMsmile (talk) 22:48, 16 April 2024 (UTC)

Could we come up with a better section heading for the section that is currently titled "solar geoengineering"? All the other section headings are clear and generic, except for this one. Here is the table of content's structure to date:

History
Causes
Relationship to climate change
Past and present
Future
Relationship to hydrological cycle
Solar geoengineering

Maybe change it to: "Relationship with xxx" or "Applications" or "Interactions with xx"? EMsmile (talk) 13:49, 16 January 2024 (UTC)

I've changed it to "Possible role in solar geoengineering". Good? EMsmile (talk) 10:34, 16 April 2024 (UTC)
"Possible role" implies that solar geoengineering could work without the existence of global dimming, which is really not the case. I changed it to "Relevance for solar geoengineering" instead. Also changed Clayoquot's subheading for contrails to hopefully clarify that altogether, they just have very little relevance next to the others. InformationToKnowledge (talk) 14:50, 16 April 2024 (UTC)
Thanks, that's better. - I wish some of the long paragraphs were still broken into two. They make for difficult reading when they are so long... like walls of text. Would you be able to break some of the really long paragraphs into two at logical points in the flow of text? I think that would be helpful. EMsmile (talk) 22:38, 16 April 2024 (UTC)

@PSA: All three issues should be addressed by now.

For [25], the reference to those two countries appeared left over from an earlier version of the page, so I removed it and provided additional verification for the rest through a review paper mentioning those studies.
For [50], I decided to instead replace the neighbouring offline source, [51], with two online references specifically addressing those points about role of wet-bed combustion and developed country policies.
With [120], it was not cited correctly in the pre-GA version of the page, and the issue was not fully addressed during the review. I found it easier to rewrite the paragraph and use a different, live reference.
Thank you for paying attention to these details. InformationToKnowledge (talk) 22:35, 5 May 2024 (UTC)