This is an archive of past discussions about Global dimming. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.
I have no fondness, but at least one Reference mentions "possible agricultural consequences", which suggests there may be some effects in references. (SEWilco18:13, 16 May 2005 (UTC))
The 9/11 plane groundings
When Horizon showed the graph before during and after the plane groundings the before and after (not during) had a noticeable difference so the difference in temperature was neglibleShiney 06:35, 14 Jan 2005 (UTC)
My guess is that they show very simplified graphics (i.e. three values on a bar graph) but that the analysis behind these results is somewhat more thorough and we are not given that in the programme. The researcher said that it had not been observed in 30 years so it can't be negligable - the point being the way it 'jumped' then returned to what was presumably a smooth curve if we had seen the whole month for example.
Travis, D.J., Carleton, A.M., and R. Lauritsen (2002). "Jet Contrails and Climate: Anomalous Increases in U.S. Diurnal Temperature Range for September 11-14, 2001." Nature, Vol. 418, p. 601. This is just a short communication . For 11–14 September 2001 the diurnal temperature range is 1.1 degrees C over normal 1971–2000 values whereas the three-day periods either sidehad temperature ranges near or below the mean. On average the diurnal temperature range for the post 9/11 period is 1.8 degrees C higher than the two three day periods before and after.
Regional variations in US diurnal temperature range for the 11-14 September 2001 aircraft groundings: Evidence of jet contrail influence on climate, Travis DJ, Carleton AM, Lauritsen RG, JOURNAL OF CLIMATE 17 (5): 1123-1134 MAR 2004. Abstract:"During the 11-14 September 2001 grounding period natural clouds and contrails were noticeably absent on high-resolution satellite imagery", "the regionalization of the DTR anomalies during the September 2001 'control' period implies that contrails have been helping to decrease DTR in areas where they are most abundant".--NHSavage22:06, 23 February 2006 (UTC)
Effect on Plants
I have noticed that wherever global dimming is mentioned, it is coupled along with the "we're all gonna die" theory that many scientists seem to have adopted.
Imagine that the Earth is a glass box with a small tree inside, and above there is a light bulb.
The rate the plant will photosynthesize depends on the concentration of CO2 in the surrounding atmosphere, and the light intensity.
So if you try and increase the concentration of CO2 in the box, the plant will start growing more quickly, and CO2 levels will drop.
But if we introduced the global dimming effect (by turning down the light) then (surprise, surprise) the plant cannot photosynthesize as much as previously and is limited by the low levels of light. Therefore the CO2 level rises.
Is this worth mentioning?
Plants might even shed more CO2 than they split if they don't get enough light. Plants must burn caleries to live just as we do. I think I read somewhere that many types of plants will not grow as well if the CO2 levels get much higher. Marksda00:30, 29 May 2006 (UTC)
I added links to two articles on www.realclimate.org on the issue. I don't have the time to work their content in, but they might serve as a good starting point for anyone who is going to dig in deeper.--84.151.204.4 12:19, 24 Mar 2005 (UTC)
realclimate.org is a blog. However, I found Journal references for many of the links you provided. Thanks for your help.Kgrr21:11, 11 March 2007 (UTC)
Are Irradiance and Insolation complete synonyms? There are two words, so what is the difference? Should the article refer to both, or just leave it as a See also? William, can you fill me in on this?? Kgrr13:17, 13 March 2007 (UTC)
Insolation (now commonly referred as irradation) differs from irradiance because of the inclusion of time. Insolation is the amount of solar energy received on a given area over time measured in kilowatt-hours per square meter (kwh/m2) Irradiance is the amount of solar energy received on a given area measured in kilowatts per square meter (kw/m2)[1].Kgrr14:47, 14 March 2007 (UTC)
Early Reports
I would like to propose a change in the Research section. Budyko's work attracted interest, but was overlooked because they thought that clouds would blanket the earth and warm it. It's only later in the 1990's when the Global warming / Global dimming paradox was discovered.
From:
The Wikipedia article states: "Early reports of "global dimming" attracted little interest, perhaps because the term itself had not yet been coined.[citation needed] The earliest reports seem to be by M. Budyko: "The effect of solar radiation variations on the climate of the Earth" in 1969, published in Tellus.[1]"
To:
One of the early reports to quantify the effects on clouds on the earth's radiation budget is described in a Technical Report by London [London 1957]. He found that clouds have a net cooling effect on the climate system. Mikhail Budyko worked with simple two-dimensional energy-balance climate models to investigate the reflectivity of ice [Budyko 1969]. He found that the ice-albedo feedback created a positive feedback loop in the Earth's climate system. The more snow and ice, the more solar radiation is reflected back into space and hence the colder Earth grows and the more it snows. Other studies confirmed that pollution or a volcano eruption could snap us into an ice age.
[Rasool and Schneider (1971)][Lockwood (1979)]
London, J. (1957) A study of the atmospheric heat balance. Final report AFC-TR-57-287 OTSPB129551 99pp, College of Engineering, New York University.
Rasool, S. Ichtiaque, and Stephen H. Schneider (1971). "Atmospheric Carbon Dioxide and Aerosols: Effects of Large Increases on Global Climate." Science 173: 138-141.
Lockwood, John G. (1979). Causes of Climate. New York: John Wiley., p. 162.
I would like to propose another change in the Research section. The Paradox between the sunlight dimming and yet the ground temperatures rising is not adequately described in this article. Atsumu Ohmura is pretty much the one that discovered Global dimming.
From: From the late 1980s onwards, scientists independently began working on solar radiation datasets and discovered declining trends worldwide; Atsumo Ohmura Secular variation of global radiation in Europe in 1989[5]; Vivii Russak in 1990 "Trends of solar radiation, cloudiness and atmospheric transparency during recent decades in Estonia"[6], and Beate Liepert in 1994 "Solar radiation in Germany - Observed trends and an assessment of their causes"[7]. Dimming has been observed in sites all over the Former Soviet Union [8]. Gerry Stanhill who studied these declines worldwide in many papers (see references) coined the term "dimming"[9].
To: In the mid-1980's Atsumu Ohmura, a geography researcher at the Swiss Federal Institute of Technology, found something that left him in a shock. He found that solar radiation striking the Earth's surface had declined by more than 10% over the three previous decades. His findings are in apparent contradiction to global warming - the global temperature has steadily been going up. Less light reaching the earth would mean that it would have to cool as London had predicted. Atsumu Ohmura published his findings "Secular variation of global radiation in Europe" in 1989[5]. This was soon followed by others. Vivii Russak in 1990 "Trends of solar radiation, cloudiness and atmospheric transparency during recent decades in Estonia"[6], and Beate Liepert in 1994 "Solar radiation in Germany - Observed trends and an assessment of their causes"[7]. Dimming has also been observed in sites all over the Former Soviet Union [8]. Gerry Stanhill who studied these declines worldwide in many papers (see references) coined the term "Global dimming"[9].
This should leave the reader with a couple of questions 1) Why is the ground getting hotter when it's getting less sunlight? 2) What happened to energy from the sun? Is it warming the upper atmosphere, or getting reflected? Instead of presenting a bunch of facts, we need to urge the reader to read on.
Where does "as London had predicted" come from? There is only one mention of London in the article and thats not relevant to this point (in fact its not clear why L is in there at all) William M. Connolley21:08, 19 March 2007 (UTC)
Ok Should I remove the reference to London altogether, or change it to Budyko's climate model? Kgrr22:58, 19 March 2007 (UTC)
I will go without it then and integrate this new paragraph. Except how the Bay Bridge picture lays across the text, I'm starting to like the article. Considering the Global warming article defers the relationship with Global dimming to the Global dimming article, we should probably bolster that section too. After that, we should consider re-submitting soon in time for Earth Day Kgrr14:55, 20 March 2007 (UTC)
Relationship to Hydrological Cycle
Do we need a section relating Global dimming to the hydrological cycle? Or should this get included in the Effects on rainfall pattern section?
Pollution produced by humans may be seriously weakening the Earth's water cycle - reducing rainfall and threatening fresh water supplies. A new study by researchers at the Scripps Institution of Oceanography suggests that tiny particles of soot and other pollutants are having a far greater effect on the planet's hydrological cycle than previously realized.Cat Lazaroff (2007-12-07). "Aerosol Pollution Could Drain Earth's Water Cycle". Environment News Service.
"Through INDOEX we found that aerosols are cutting down sunlight going into the ocean," added Ramanathan. "The energy for the hydrological cycle comes from sunlight. As sunlight heats the ocean, water escapes into the atmosphere and falls out as rain. So as aerosols cut down sunlight by large amounts, they may be spinning down the hydrological cycle of the planet."
In the new "Science" article, Ramanathan, Crutzen, J.T. Kiehl of the National Center for Atmospheric Research, and Rosenfeld of the Hebrew University of Jerusalem, say the aerosol issues raised by INDOEX are a "major environmental concern." I need to find this reference.
I had a look at the article. It reads quite well and the links at the end
should allow people to follow it up.
A few suggestions.
(1) In the research section, 5 lines down. "Other studies confirmed that
pollution...". How about, speculated instead of confirmed.
(2) Last para. in Research section where you list the numbers. Note that
these numbers are for the terrestrial surface and not really a global
average. Whether dimming (or brightening) occurred over the ocean has been a
bit of an unknown.
(3) Typo on the second last line of Pan Evaporation Section. i.e. "fills in
the gaps in the paps in the data."
(4) Recent Reversal of the Trend. I did not understand the first para. I
agree that Wild et al. claimed brightening since 1990. They did this using
measurements over land. The method used in Pinker et al. 2005 gives
continued (but small) dimming over land and brightening over the ocean.
Hence, over the land surface, Wild et al and Pinker et al disagree. There
is as yet no resolution of this that I am aware of. It is a matter of
intense research.
I agree with this comment, in the context of an overall thumbs u as regards the informativeness of the article without it assuming some "pro/con" stance on the information contained therein. In particular, the graphic provided regarding the Pinker data is in direct contradiction to the (verbal) claims of Wild et al.Chas zzz brown02:39, 25 March 2007 (UTC)
Some questions.
You may not believe it but this is the first time I have ever looked at
Wikipedia. How does it work? Did they commission you to write the article or
did you decide to contribute?
Point (4) seems to be correct. I don't have access to Science now, but the RC post agrees. I've rewritten this bit since (a) it read like Pinker had reconfirmed but Wild had; I've added the P/W diff William M. Connolley16:08, 24 March 2007 (UTC)
Relationship to global warming
We really need to add more information into this one section. The Global warming article defers answering this relationship to Global dimming and here is the grand total of what explains the relationship:
Further information: Global warming
Some scientists now consider that the effects of global dimming have masked the effect of global warming to some extent and that resolving global dimming may therefore lead to increases in predictions of future temperature rise.[15]
In a paper published March 8 in the American Geophysical Union's Geophysical Research Letters, a research team led by Anastasia Romanou of Columbia University's Department of Applied Physics and Mathematics, New York, also showed that the apparently opposing forces of global warming and global dimming can occur at the same time.Kgrr14:53, 21 March 2007 (UTC)
"Masking of Global Warming
The surface dimming due to ABCs has a surface cooling effect, which
should have masked some of the surface warming due to greenhouse gases.
The magnitude of this masking effect is one of the central problems in climate
change with significant implications for future climate changes and
policy responses to global warming (Andreae et al., 2005). The extent of
global warming is not fully reflected in the Earth’s observed surface temperatures.
The additional heat trapped by the increase in greenhouse gases
from the late nineteenth century to the present time should have committed
the planet to a global warming in the range of 1ºC to 3ºC (see
Ramanathan, 1988 for an explanation of the term committed warming). The
observed global surface warming is only about 0.6 K, i.e., only about 20%
to 60% of the committed warming (depending on whether we use 3 K or 1
K for the committed warming). Some of this warming has been masked by
the dimming due to brown clouds and the remaining heat is stored in the
depths of the ocean to be released in the coming decades to centuries.
Through the process of convective overturning, oceans transfer infrared
energy to their deepest layers and hold the heat, delaying the impact of
global warming. Whether this stored heat will warm the atmosphere in a
few decades or a few centuries is unknown.
Current estimates of the ABC masking effect range from 30% to as high
as 75% (Crutzen and Ramanathan, 2003; also see Andreae et al. in this issue
for a more detailed consideration of the aerosols’ masking effect). The fundamental
issue with this large range of uncertainty of the masking effect is
that, policies to reduce ABCs (due to their effects on health, acid rain and
agriculture) will unmask the cooling effect of ABCs quickly and have a
potentially large effect in the acceleration of global warming. This is
because the lifetime of ABCs is a few weeks and hence their masking effect
will diminish as soon as their emissions are curtailed, whereas GHGs will
respond to emission reduction policies on decadal to century time scales.
Without a better quantification of the masking effect of ABCs, we would not
know whether warming in the coming decades (if it were to occur) is due
to the unmasking effect of ABCs (by efforts of cleaning up in Asia for example),
or due to release of stored greenhouse heating in the oceans, or continued
increase in emission of greenhouse gases. In the meantime, every
decade we delay in taking action, we are committing the planet to additional
warming that future generations have to deal with."
V. Ramanathan http://www-ramanathan.ucsd.edu/PASScriptaVaria106.pdf
Ramanathan, V., 2006: “Atmospheric Brown Clouds: Health, Climate and Agriculture Impacts” in the Pontifical Academy of Sciences Scripta Varia 106 Interactions Between Global Change and Human Health, (Pontifica Academia Scientiarvm 2006), pp. 47-60.
Kgrr03:01, 28 March 2007 (UTC)
"But perhaps the most alarming aspect of global dimming is that it may have led scientists to underestimate the true power of the greenhouse effect.
They know how much extra energy is being trapped in the Earth's atmosphere by the extra carbon dioxide we have placed there.
What has been surprising is that this extra energy has so far resulted in a temperature rise of just 0.6 degree Celsius.
This has led many scientists to conclude that the present-day climate is less sensitive to the effects of carbon dioxide than it was, say, during the ice age, when a similar rise in CO2 led to a temperature rise of six degrees Celsius.
But it now appears the warming from greenhouse gases has been offset by a strong cooling effect from dimming - in effect two of our pollutants have been cancelling each other out.
This means that the climate may in fact be more sensitive to the greenhouse effect than previously thought.
If so, then this is bad news, according to Dr Peter Cox, one of the world's leading climate modellers.
As things stand, CO2 levels are projected to rise strongly over coming decades, whereas there are encouraging signs that particle pollution is at last being brought under control.
"We're going to be in a situation unless we act where the cooling pollutant is dropping off while the warming pollutant is going up.
"That means we'll get reducing cooling and increased heating at the same time and that's a problem for us," says Dr Cox.
Even the most pessimistic forecasts of global warming may now have to be drastically revised upwards.
That means a temperature rise of 10 degrees Celsius by 2100 could be on the cards, giving the UK a climate like that of North Africa, and rendering many parts of the world uninhabitable.
That is unless we act urgently to curb our emissions of greenhouse gases."
"Could Reducing Global Dimming Mean a Hotter, Dryer World?
Despite concerns over global warming, scientists have discovered something that may have actually limited the impact of greenhouse gases in the atmosphere in recent years by reducing the amount of sunlight reaching the surface of the Earth.
In research they published last year in the journal Geophysical Research Letters, a team led by Beate Liepert at the Lamont-Doherty Earth Observatory reported that they found a measurable decline between 1950 and 1990 in the amount of sun reaching the Earth's surface. The team concluded that solar radiation is being reduced by growing quantities of man-made particles in the atmosphere—in particular those produced by burning fossil fuels. This increase in small particles of ash, soot and sulfates has also caused the cloud cover to thicken in recent decades, further reducing solar irradiance. Only recently have climate models begun to include them in predictions of future global warming.
(Global dimming was the subject of a recent special on the PBS science series NOVA featuring Beate Liepert.)
"Aerosols are highly variable in space and time, which is why aerosol forcing of climate is generally very difficult to include in climate studies," said Liepert. "Furthermore, aerosols are found near the Earth's surface and affect mainly the fluxes of energy and water at the surface. These new ideas on the affects of aerosols might open up many avenues and solve more discrepancies in the climate change debate."
It is widely agreed that greenhouse gasses in the atmosphere are causing temperatures to rise around the world. What has not been considered until recently is how temperatures would respond if the aerosol layer and cloud cover were not reflecting some of the suns radiation away from the planet. Liepert and her co-authors also concluded that the imbalance between a decline in solar radiation and warming surface temperatures will lead to weaker turbulent heat fluxes and reduced evaporation and precipitation, which could ultimately lead to a more humid atmosphere in which it rains less.
Although rising temperatures should increase the amount of moisture in the atmosphere, the research shows that human-produced airborne aerosols can cause water to condense to form more, but smaller, cloud droplets. This process is likely contributing to the observed thickening of the Earth's cloud cover. However, smaller droplets are not heavy enough to sink through the air as rain. As a result, the cloud cover lasts longer and there is less rain.
"Water has a characteristic residence time in the atmosphere before it gets rained out. In a warmer world, this residence time is longer because a warmer atmosphere can hold more water," said Liepert. "Aerosols affect clouds by suppressing rain and increasing its residence time."
Examples of data supporting this new hypothesis include studies indicating a steady decline of water evaporation in the Northern Hemisphere over the past 50 years. Over the last 60 years, large regions of Eurasia have seen soil moisture increase by more than one centimeter per decade, yet no significant changes in precipitation are being seen.
Global dimming also resulted in an observable difference in the brightness of sunlight. Even in remote areas, the atmosphere was more polluted and therefore darker. In the end, successful efforts to reduce emissions and clean up air pollution around the world could cause the full effect of global warming to become more noticeable in the near future.
"We thought we live in a global warming world, but this is actually not right," Liepert said in a BBC interview last year. "We lived in a global warming plus a global dimming world and now we are taking out global dimming. So we end up with the global warming world, which will be much worse than we thought it will be, much hotter." "
Could Reducing Global Dimming Mean a Hotter, Dryer World?
Earth Institute News
posted 04/14/06
Contact: Ken Kostel
212-854-9729 or kkostel@ei.columbia.edu
The "relation to GW" should be dealt with here rather than in GW, cos thts too big already. Note that what this article doesn't really explain very well at the moment is that although direct radiation decreased by 4%-ish, the actual energy into the climate system didn't by anything like that, or we'd have seen massive cooling. So although GD has masked GW somewhat, it hasn't stopped it, and there has been a fairly fine balance William M. Connolley08:27, 2 April 2007 (UTC)
pan evaporation data as the most convincing evidence of global dimming ?
k insists on adding:
Scientists regard the pan evaporation data as the most convincing evidence of global dimming due to the simplicity and repeatability of the experiment.
to this and the GW article. I don't believe it. As the article says:
From the late 1980s onwards, scientists independently began working on solar radiation datasets and discovered declining trends worldwide
ie, its radiation measurements that are evidence for dimming. The article continues:
Atsumo Ohmura Secular variation of global radiation in Europe in 1989; Vivii Russak in 1990 "Trends of solar radiation, cloudiness and atmospheric transparency during recent decades in Estonia", and Beate Liepert in 1994 "Solar radiation in Germany - Observed trends and an assessment of their causes"
Again: the evidence is *radiation* measurements. Against these scientific papers, k sets a Tv programme which doesn't cite any source for its claim.
My understanding is that the various researchers were causing confusion and consternation and it was the pan studies - which were far more world ranging, and relied on for so long, that convinced people it wasn't some temporary local phenomena or weird affect. Now finding a citation that says the pan studies were so important. So I agree with the stance, but it should be based on citation --Smkolins03:24, 11 March 2007 (UTC)
It was mentioned in the BBC program, but that's just a TV program. So I have for now added the statement that the pan data corroborates the radiometer findings. As mentioned in the program, the pans don't have calibration problems and it's an easy experiment that anyone can repeat. Kgrr16:29, 11 March 2007 (UTC)
I have no problem with that. As Raymond A said, yes the data is simple but interpreting it isn't, since it depends on far more tahn just radiation. But that is another matter William M. Connolley16:49, 11 March 2007 (UTC)
Could you consider an interview of some of the notable authors that are cited in this piece?
BBC program and transcript
<quote>DR BEATE LIEPERT: My friends' reaction actually to Gerry's and to my work at the same time too was, oh my God this is really extreme, you are um contradicting global warming. Er do you know how many billions of dollars was spent on global warming research and you and this old guy er are contradicting er us.
NARRATOR: So Liepert and Stanhill's work was widely dismissed. But Global Dimming was not the only phenomenon that didn't seem to fit with Global Warming. In Australia two more biologists, Michael Roderick and Graham Farquhar were intrigued by another paradoxical result - the world-wide decline in something called the pan evaporation rate.
PROF GRAHAM FARQUHAR (Australian National University): It's called pan evaporation rate because it's evaporation rate from a pan. Every day all over the world people come out in the morning and see how much water they've got to add to a pan to bring it back to the level it was the same time the morning before. It's that simple.
NARRATOR: In some places agricultural scientists have been performing this rather dull daily task for more than a hundred years. PROF GRAHAM FARQUHAR: The long-term measurements of pan evaporation are what gives it its real value.</quote>
They are saying that they were not taken seriously on the radiometer data until the pan evaporation data was presented. Pan evaporation is taken as prima facie evidence of global dimming. The radiometer data was dismissed due to possible calibration errors.
Ok .. a television interview of the experts is not good enough for you. Please remember NPOV before you respond with your OPINION Kgrr22:19, 11 March 2007 (UTC)
Sigh. You are doing your best to personalise this. Take out the narrators words and consider what the scientists are saying. B+L say nothing about PE. GF describes how to do it, and then says its valuable because it has long term records. Neither says its the best/prima-facie/whatever evidence for GD. (Note that if the evidence goes back 100y, why don't we have GD evidence back 100y from this stuff? Answer: because you can't turn PE into GD; you can only interpret the PE once you know about GD already) William M. Connolley22:41, 11 March 2007 (UTC)
Sighhhhhh You really argue for the sake of argueing, don't you? You never even read the initial link I gave. Do a Google Scholar search on "pan evaporation" and "global dimming". It's all over the literature. Both methods are seen as evidence of global dimming.
Why is it that farmers would complain about needing less water for their fields? They never complained that it takes slightly less and less water, decade after decade. Scientists overlooked the source of data as they explain in both the BBC and NOVA pieces. It happens. But now that they have found the data, they see it as very reliable data to prove their hypothesis. There are loads of examples where scientists have a hypothesis and stumble over data that they themselved did not collect. Core samples are another example of this.
Unfortunately, I think the BBC narrator sums it up pretty well:
NARRATOR: It was the same with Europe and the USA. The drop in evaporation rate matched exactly the drop in sunlight reported by Beate Liepert and Gerry Stanhill. Two completely independent sets of observations had come to the same conclusion. Though it seemed incredible, there was no doubting Global Dimming now.
Both pan evaporation and radiometry are prima facie evidence of global dimming. You just refuse to want to acknowledge this fact. Note that I never said that radiometry was not prima facie either. Kgrr05:43, 12 March 2007 (UTC)
I wonder if you even bother to read the text you insert. Why did you put it in? It doesn't prove your point, as I said above, and you haven't contested that William M. Connolley09:32, 12 March 2007 (UTC)
of course I do. YOU WIN - Since you believe that David Sington is just one of just a few isolated fools, let's just go with "BBC Horizon producer David Sington believes that many climate scientists regard the pan-evaporation data as the most convincing evidence of solar dimming."Kgrr10:21, 12 March 2007 (UTC)
I believe that television documentaries often have a tendency to use over-dramatic words. I don't see why you aren't happy to stick to the science. Find some nice published refs William M. Connolley10:34, 12 March 2007 (UTC)
I could not agree more. Some TV sources here in the US like Fox News are sources of disinformation. A tabloid would be a better source. Believe me, I'm working on it.Kgrr13:17, 13 March 2007 (UTC)
From the FAQ-
Is there a possibility that the pan-evaporation method is too crude to be reliable?
Rather the reverse. It is the very simplicity of the pan-evaporation experiments that makes them reliable and comparable between different locales and over long periods of time. That is why many climate scientists regard the pan-evaporation data as the most convincing evidence of solar dimming.
Horizon producer David Sington answers questions about global dimming.] Science and Nature - TV & Radio Follow-up--Smkolins21:01, 2 April 2007 (UTC)
confused by language
several places it refers to the amount of dimming but it seems to me to be inconsistent in how - and implying widely different values.... "of the order of a 4% reduction over the three decades from 1960–1990", "declined by more than 10% over the three previous decades", "average estimated at around 2–3% per decade", 5.3% (9 W/m²); over 1958–85 (Stanhill and Moreshet, 1992), 2%/decade over 1964–93 (Gilgen et al, 1998), 2.7%/decade (total 20 W/m²); up to 2000 (Stanhill and Cohen, 2001), 4% over 1961–90 (Liepert 2002)[13][14]" - mainly there are two forms reported - x% "over" decades, and x% "per" decade. Those two seem widely different to me - if I hear something changed over some decades I hear it took those decades to cover that stated change, not that it changed that amount each decade. Am I the only one? Can we adjust the phrasing or is it being driven by the sources? Or has this been some kind of huge issue trying to figure out what's going on? I mean a 4% change is a hugely different value than 75% change if they are to be over the same period of time.--Smkolins20:04, 2 April 2007 (UTC)
The phrasing of the findings is driven by the way the journal articles present their findings. It would be nice if they all reported the same units over the same time period. I imagine the difficulty of saying something is significant if the change is only 0.2% per year. So, the scientists express the results in x% per decade or x% over the course of their study. Even if all the data were normalized to say x% der decade, which dates covered and where the samples were taken makes these studies even more difficult to compare. Kgrr17:33, 5 April 2007 (UTC)
Relation to Agriculture
Acid rain -> Reduced crop yeilds
Reduction of photosynthesis -> Reduced crop yeilds
ATMOSPHERIC BROWN CLOUDS:
HEALTH, CLIMATE AND AGRICULTURE IMPACTS
VEERABHADRAN RAMANATHAN
http://www-ramanathan.ucsd.edu/PASScriptaVaria106.pdf
Ramanathan, V., 2006: “Atmospheric Brown Clouds: Health, Climate and Agriculture Impacts” in the Pontifical Academy of Sciences Scripta Varia 106 Interactions Between Global Change and Human Health, (Pontifica Academia Scientiarvm 2006), pp. 47-60.
Interesting summary on global dimming [2] My concern here is the reference. It's readable to everyone through Common Dreams, a progressive news agency, but one needs to register to see it on the New York Times site. Kgrr13:27, 13 March 2007 (UTC)
I am researching this and finding news articles. I will hope to uncover a few good Journal articles as well. For now, I am collecting the references in the external references section.Kgrr15:36, 13 March 2007 (UTC)
Note that the effect (2–3%, as above) is due to changes within the Earth's atmosphere; the value of the solar radiation at the top of the atmosphere has not changed by more than a fraction of this amount.[citation needed]
The largest reductions are found in the northern hemisphere mid-latitudes [citation needed]
This claim is not universally accepted and is very difficult to test.[citation needed]
Independent research in Israel and the Netherlands in the late 1980s showed an apparent reduction in the amount of sunlight was fixed by SEWilco while I was working on it. I had deleted the reference because the URL was no longer vaid. Thanks!Kgrr21:34, 11 March 2007 (UTC)
I've re-written most sections and added materials to all sections except one - relationship to Global Warming. (see below) Kgrr15:38, 24 March 2007 (UTC)
A good article has the following attributes.
1. It is well written.
2. It is factually accurate and verifiable.
3. It is broad in its coverage.
4. It follows the neutral point of view policy.
5. It is stable
6. It contains images, where possible, to illustrate the topic.
Not just plants - how about astronomy? Could global dimming relate to recent "discoveries" like distant supernova being "too dim" and thus provide evidence for "Dark Energy"? No reference yet that i know of. —The preceding unsigned comment was added by Smkolins (talk • contribs) on 20:42, 20 April 2006.
This is completely unrelated to observations of distant light sources, including supernovae. Earth's surface is receiving varying amounts of light due to its atmosphere's composition changing. When observing sources outside the atmosphere, telescopes are calibrated against outside sources of known brightness. Also, at least some of the observations of distant objects were performed with space-based telescopes that aren't affected by Earth's atmosphere. --Christopher Thomas21:00, 20 April 2006 (UTC)
I can think of two components affecting the depth of light into the ocean
First- as the light coming through the skies have dimmed the depth to which light could penetrate must decrease.
Second- as some of this dust must wash out into the oceans over time I suppose the ocean is more cloudy than before (I can't say whether it would be more reflective or not - maybe?)
From the above I wonder about life dependent on light near the surface....
And another affect - I wonder if the muds of the ocean bottom would show signs of these smaller dust particles being included - are mud slides easier with these additions?
This is all in addition to the prior known, if debated, effects of global warming on the oceans (volume increases from heating to being added by melt water.) --Smkolins18:46, 7 May 2006 (UTC)
GD is (probably) mostly occurring over land (due to pollution being there). Further, light doesn't penetrate far into the oceans anyway. Also, the aerosol is largely soluble William M. Connolley18:55, 7 May 2006 (UTC)
This seems to be against several statements, for example the Global_dimming#Probable_causes section measures issues near Maldives - 435 miles south of India. Now the southern Islands weren't affected while the nothern ones were by this specific measurement. I presume the northern islands were affected by a airflow but that airflow hadn't evenly spread out around the Indian ocean basin air region. I wonder how far it reached? Africa?--Smkolins20:12, 2 April 2007 (UTC)
I read through the article twice and I was impressed by the article's depth and breadth. It passes all the good article criteria. It was very well written, neutral, well-sourced, pictures do illustrate the topic, and seems to be fairly stable as of this moment. Congratulations.
Cronholm14423:17, 12 April 2007 (UTC)
Past tense?
Recent edits (in particular this edit and this one) have changed the introduction to imply that global dimming is completely a thing of the past. But is it truly a thing of the past or is it merely somewhat less pronounced than it was previously? (My understanding is that although there is a reversal in progress, the earth's surface still gets less solar energy now than it did previously-- say, before the industrial revolution. So I would argue that global dimming should still be referred to in the present tense.)
To clear up this confusion, someone more knowledgeable than I needs to present evidence to answer the following two questions. (1) Has the amount of solar energy reaching the earth returned to the levels of past millenia? (2) Does the word "dimming" in global dimming mean "it continues to get dimmer" or does it instead mean "it's dimmer than it was". (Since I do not have full access to the journal articles cited, I cannot easily research this on my own.)
Riick06:46, 29 April 2007 (UTC)
Measurements do not exist from former time to fully answer that. Dimming - as in getting dimmer - is definitely over. Brightening - as in getting brighter, at least in direct radiation - is in progress. I don't know about absolute values though William M. Connolley09:54, 29 April 2007 (UTC)
Caption to the Golden Gate bridge picture
I made this edit changing the caption of the picture from "Golden Gate Bridge with California's characteristic brown cloud in the background -- the most likely cause of global dimming." to "Golden Gate Bridge with California's characteristic brown cloud in the background -- a likely contributor to global dimming."
Since then, User:Kgrr left the following message on my Talk Page:
Your edit: the most likely cause of global dimming. -> a likely contributor to global dimming.
The primary cause of Global Dimming IS thought to be global brown clouds - moreso now in places like China and India. Did you read the papers? Perhaps you can re-word your edit. Kgrr13:24, 15 May 2007 (UTC)
So... one of my concerns with the caption is that the poor juxtaposition of phrases suggests that "California's characteristic brown cloud" is the most likely cause of global dimming. That is assuredly not what is meant. I believe that Kgrr intends the caption to say that "brown clouds are the most likely cause of global dimming". If that assertion is true, we should rephrase the caption to make that clear. Something like "A picture of California's characteristic brown cloud. Brown clouds are thought to be the most likely cause of global dimming."
However, I am not convinced that low-lying brown clouds like the one in the image are the most likely cause of global dimming.
First of all, I admit to being fairly ignorant of the subject matter and more than willing to be corrected if I am wrong. I will tell you what I understand from reading this article. I admit to not having read any of the references.
The article states that aerosols, particularly black soot, are responsible for global dimming by reflecting sunlight back into space and by forming the nuclei of clouds which also reflect sunlight back into space. The article doesn't say "brown clouds". Now, it may be obvious to everybody else that "black soot = brown clouds" but it isn't obvious to me.
I also note that the article says "Though black carbon, most of which is soot, is an extremely small component of air pollution at land surface levels, the phenomenon has a significant heating effect on the atmosphere at altitudes above two kilometers (6,562 feet)." I'm not sure what to make of this sentence. Global dimming asserts a cooling effect due to reduced sunlight. Are we saying that black carbon heats up the atmosphere above 2km altitude and thereby cools the atmosphere below 2km altitude?
In any event, it's not clear that the brown clouds in the Golden Gate picture represent black carbon above 2km altitude. I am under the impression that the effect of aerosols on global dimming occurs at higher altitudes than the low-lying smog shown in the Golden Gate picture. My reasoning is that, by the time sunlight, reaches the lower altitudes, the energy is already in the atmosphere and it's too late to reflect it back into space. This is supported by the fact that jet contrails are generally left at high altitudes (30,000 to 40,000 feet). It is also supported by Budyko's proposal to burn "sulfur in the stratosphere" where presumably it would have a greater effect than in the lower atmosphere.
Once again, I admit to being a naïf in this area so please correct any misconceptions or errors in reasoning.
China and India are major contributor to the brown clouds of smog — mostly black carbon, organic carbon and other aerosols such as sulphates and nitrates — formed by wildfires and by burning fossil fuels and biofuels."Box1. Brown clouds cast a dark shadow".
The brown cloud "NASA Eyes Effects of a Giant 'Brown Cloud' Worldwide". routinely climbs high enough into the atmosphere to hitch a ride on the fast-moving jet stream heading east to North America. In April and May, when seasonal winds are strongest, the high-altitude pollution can cross the Pacific in as little as four days. Since it's being carried by the jet stream, it's as high as 10km.
From the ground, it looks just like the brown cloud you see over San Francisco. The picture is deceiving. Look how high it is above the ridge behind Berkely. You are looking at an aggregate for about 20-25 miles. The smog you see in the picture reaches 10-15,000 feet. I fly from Seattle to SFO regularly.
I guess you need to see a space shuttle launch before you can appreciate how thin our atmosphere really is. When I lived in Boca Raton, FL, we used to watch space shuttle launches. At first it really surprised me as to how low an 80 mile orbit looks from the ground.
Perhaps the pictures caption and the connection between global dimming and atmospheric brown clouds should be made clearer. Kgrr14:37, 17 May 2007 (UTC)
Edward Teller's Work
It would also be worth mentioning Edward Teller's work, which can be found here:
Teller's new idea seems to be the use of metallic resonant scatterers, which are much more effective than soot or rock dust. He also suggested that a cloud of these particles could be placed at the interior Lagrange point of the Earth/Sun. DonPMitchell01:17, 15 November 2007 (UTC)
As part of the WikiProject Good Articles, we're doing sweeps to go over all of the current GAs and see if they still meet the GA criteria. I'm specifically going over all of the "Meteorology and atmospheric sciences" articles. I believe the article currently meets the majority of the criteria and should remain listed as a Good article. However, in reviewing the article, I have found there are some issues that need to be addressed. I have made minor corrections and have included several points below that need to be addressed for the article to remain a GA. Please address them within seven days and the article will maintain its GA status. If progress is being made and issues are addressed, the article will remain listed as a Good article. Otherwise, it may be delisted. If improved after it has been delisted, it may be nominated at WP:GAN. This article covers the topic well and if the above issues are addressed, I believe the article can remain a GA.
Needs inline citations:
"It is thought that global dimming was probably due to the increased presence of aerosol particles in the atmosphere caused by human action."
"It is also thought that the water droplets in clouds coalesce around the particles."
"Global dimming has interfered with the hydrological cycle by reducing evaporation and may have caused droughts in some areas"
The lead needs to be expanded to two or three paragraphs to better summarize the article. See WP:LEAD for guidelines.
"In essence, the sources of both greenhouse gases and air particulates must be addressed." This last sentence in the article does sound like a good idea, but it appears to be POV. It should either be reworded or removed completely for readers to make their own conclusions.
I will leave the article on hold for seven days, but if progress is being made and an extension is needed, one may be given. I will leave messages on the talk pages of the main contributors to the article along with related WikiProjects so that the workload can be shared. If you have any questions, let me know on my talk page and I'll get back to you as soon as I can. Happy editing! --Nehrams2020 (talk) 05:46, 3 April 2008 (UTC)
Progress so far
Issue #1: "It is thought that global dimming was probably due to the increased presence of aerosol particles in the atmosphere caused by human action."
Issue #3: "The lead needs to be expanded to two or three paragraphs to better summarize the article. See WP:LEAD for guidelines.
"In essence, the sources of both greenhouse gases and air particulates must be addressed." This last sentence in the article does sound like a good idea, but it appears to be POV. It should either be reworded or removed completely for readers to make their own conclusions."
Issue #4: "In essence, the sources of both greenhouse gases and air particulates must be addressed." This last sentence in the article does sound like a good idea, but it appears to be POV. It should either be reworded or removed completely for readers to make their own conclusions."
Good job so far. The lead still needs to be expanded and the new inline citation needed request needs to be fixed. I'll continue to leave the article on hold for those two issues to be fixed. I struck through the ones that have already been corrected. If you have any questions, let me know on my talk page and I'll get back to you as soon as I can. --Nehrams2020 (talk) 01:42, 12 April 2008 (UTC)
GA Sweeps Review: Pass
Good job on addressing the above issues. I believe the article continues to meet the GA criteria and the article will keep its status. I would recommend continuing to add more information to the lead that has more information within the article. As it stands now, it is sufficient, but it could always improve. Continue to expand the article with any available information, ensuring that it is properly sourced and neutral. If you have any questions, let me know on my talk page and I'll get back to you as soon as I can. I have updated the article history to reflect this review. Keep up the good work and happy editing! --Nehrams2020 (talk) 06:51, 14 April 2008 (UTC)
BBC Horizon
(William M. Connolley 23:40, 13 Jan 2005 (UTC)) All this surge of editing presumably comes from the BBC horizon documentary. Which is all very well, but basing your science on a TV programme may not be a good idea.
Unqualified and unattributed editing would indeed be unwise. Checking all the sources used by the BBC would be a very good move, especially for such a potentially important topic; hopefully someone will have the time to do that. Wikipedia is, however a "work in progress" and should be treated as such. 80.42.86.119 23:53, 13 Jan 2005 (UTC)
(William M. Connolley 00:04, 14 Jan 2005 (UTC)) Yeeeessss... but perhaps checking them *before* putting them in would make some sense too?
Agreed, a practice I follow given the time to do so, especially if the source is less reputable than the BBC. Though I know even they are capable of getting basic facts wrong too...
It's not so much that popular science media like the BBC aren't reputable or honest, but simply by dint of their programming priorites they produce material of a rather lower grade of factuality than that demanded by an encyclopedia. In particular, they're prone to:
picking the most exciting scenario from the range possible and concomitantly discounting the more prosaic.
downplaying controversy and dissent (except where the controversy is the subject of the piece, in which case they tend to overplay it)
willful conflation of correlation and causation
The Sept 11th thing is a case in point of this last issue. It's true that there's a correlation between this particular cessation of contrails and a change in temperature; but this doesn't by any means prove a causal link. Worse, as we have but a single datapoint, the correlation is very weak. The article said "with a consequent sudden drop in global dimming", but that's a far stronger statement that the evidence supports. I reworded that paragraph to be much less conclusory. -- John Fader 01:34, 14 Jan 2005 (UTC)
The question of checking sources is one I grapple with every time I want to edit the encyclopedia. To research everything to the level acceptable to, say, a degree level dissertation would simply mean I would never actually write anything given the time I have available.
It's important, in my opinion, to judge whether the inexact and uncoroborated information will be of more value than nothing at all. Or that the good will outweigh the bad. Or something. The fact that anything written will be ruthlessly weighed and edited by others is reassuring in this context. Like the proverbial fountain pen, many articles on which I write soon contain little of my original prose - but are nevertheless shaped by all contributions to them.
I would like to add a link to the section on Global Dimming on the Climate Change and Global Warming web site. It discusses the main points illustrated by the BBC's January 15, 2005 broadcast of the "Horizon" documentary. I found it a very thorough and useful source of information on the problem of Global Dimming. Here is the link: http://www.globalissues.org/EnvIssues/GlobalWarming/globaldimming.asp
Someone should review and reference useful additions from this - [3] though the included links don't work. Looks like a collections of regional studies and also one model review.Smkolins (talk) 13:08, 26 August 2009 (UTC)
Maldives "experiment"
Shouldn't this be called a study, or research, or perhaps natural experiment rather than simply an experiment? Experiment usually implies that variables are changed by the researchers. I refer to:
"Experiments in the Maldives (comparing the atmosphere over the northern and southern islands) in the 1990s showed that the effect of macroscopic pollutants in the atmosphere at that time (blown south from India)..."
It's unclear from the article whether the brightening/dimming percentages nominated are relative to the precedent planetary albedo or absolute percentages, and whether the decadal dimming percentages given are absolute or relative to the prior decade. I will abstain from making any modifications as I am not a climatologist. Eutactic (talk) 07:54, 14 May 2010 (UTC)
It's my understanding that the measurements are relative (as they are all compared to some measurement of the past) but the physical process represents an absolute decrease and I believe most or all entries report the differences as compared to some date. It's like saying "relative to the fixed stars" in that the presumption was the number from long ago (whether 50 years or 10) were constant but it turns out they are not (stars do actually move too.) There may have to be some adjustment and consistency in reporting but so far I've not seen any in the literature, though I'm not an expert in the field by any means. Smkolins (talk) 16:34, 14 May 2010 (UTC)
Do you mean stuff like Global dimming is the gradual reduction in the amount of global direct irradiance at the Earth's surface that was observed for several decades after the start of systematic measurements in the 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4% reduction? That 4% is relative to the insolation at the Earth's surface, not to the TOA radiation. That seems fairly clear to me from context.
Or "The effect varies greatly over the planet, but estimates of the terrestrial surface average value are: 5.3% (9 W/m²)...". So TOA is 1366 ish, its not that.
Apologies, the way I phrased the original topic was a bit illucid. Yes, I meant whether the reduction is expressed as a percentage of the total top-of-atmosphere insolation (which I treat as approximately invariant, or at least predictably periodic) or as a percentage change with respect to a historical surface insolation. Thanks for clearing this up. And wow, I didn't realise the surface and TOA insolations were so different. Regards - Eutactic (talk) 11:45, 17 May 2010 (UTC)
Atmosphere's not nearly as transparent as many think (plus the reflection off the surface of what is transparent). Just think of how bright Earth would be from Venus in the night sky (though not as bright as Venus is in Earth's morning/evening sky because Venus has a much higher albedo because of clouds.) Smkolins (talk) 15:40, 17 May 2010 (UTC)
THis is one of many books, written by those researching the potential effects of aerosol spraying for GeoEngineering purposes.
http://www.nap.edu/catalog.php?record_id=1605
Global warming continues to gain importance on the international agenda and calls for action are heightening. Yet, there is still controversy over what must be done and what is needed to proceed.
Policy Implications of Greenhouse Warming describes the information necessary to make decisions about global warming resulting from atmospheric releases of radiatively active trace gases. The conclusions and recommendations include some unexpected results. The distinguished authoring committee provides specific advice for U.S. policy and addresses the need for an international response to potential greenhouse warming.
It offers a realistic view of gaps in the scientific understanding of greenhouse warming and how much effort and expense might be required to produce definitive answers.
The book presents methods for assessing options to reduce emissions of greenhouse gases into the atmosphere, offset emissions, and assist humans and unmanaged systems of plants and animals to adjust to the consequences of global warming.
It appears that some people also call it solar dimming.[5]
The article is pretty interesting and has more material for the relationship between global warming and global dimming. It looks like by exporting manufacturing to China and India, Europe and the US has been cleaning up its skies and making global warming worse by removing the blanket of pollution. And of course, global is probably getting worse in India and China as they have little or no environmental regulations.
Also, should there be a section on the data deficit brought up in this reference?
Solar dimming requires the Sun to dim. Global dimming only requires that less sunlight reach the surface, and there are several possible reasons for that. Not all cases of dimming on the surface are due to dimming of the Sun. (SEWilco06:40, 14 March 2007 (UTC))
Currently Solar dimming is redirected to Global dimming. People in the past have used Solar dimming as a synonym with Global dimming. But since satellites have verified that it's not the sun that is changing, but the atmosphere, it appears that Global dimming is the culprit. Is Solar constant the correct article? Kgrr16:34, 11 April 2007 (UTC)
Indeed. Solar emmission has been neglected in publicly available NASA studies. What is emmitted from the sun is a First Order Parameter and should not be neglected in any study of earth climate. Global Warming enthusiasts seem to be quick to blame human activity which could actually result from natural phenomena. Show the evidence. --71.245.164.83 (talk) 02:57, 17 February 2011 (UTC)
Global Warming May Have Accelerated
A new NASA study has found that an important counter-balance to the warming of our planet by greenhouse gases – sunlight blocked by dust, pollution and other aerosol particles – appears to have lost ground.
Is this latest study something we want to include in the Recent reversal of the trend section? Does this graph also prompt a section or material on aerosols from volcanoes? Kgrr15:06, 21 March 2007 (UTC)
Response to this graphical evidence is lacking. The article referenced cites a question - e.g. not definitive by itself. This is a bit manipulative. "Need more data" is assumed. X-axis assumed to be Calendar year, but Y-axis is not labeled. --71.245.164.83 (talk) 03:01, 17 February 2011 (UTC)
* brown haze extends over South, Southeast and East Asia
* haze is concentrated 3 kilometers above the surface and can travel halfway around the globe in less than a week
* large surface cooling due to reduced sunlight perturbs the hydrological cycle
Brown haze composition
* black carbon and ash
* sulfates
* nitrates
* mineral dust
* 75% of the cloud is man-made
Cause
* forest fires
* inefficient cooking fuels
* factories
* motor vehicle use
Effects
* significant reduction of solar radiation to the surface by as much as 15%
* altered regional monsoon patterns (less sea evaporation from sunlight means less rain)
* less rain in northwest India, Pakistan, Afganistan, and western PRC by as much as 40%
* more rain and flooding in other areas
* reduction of photosythesis (drop in agricultural productivity)
* acid deposition and plant damage
* respiratory ailments
Extensive air pollution over Asia has drawn considerable attention from the global atmospheric science community. In India, as in other Asian countries, the government as well as scientists are wary of motivated criticism, but still have much to do to put the environment in order.
The Atmospheric Brown Cloud (ABC) or the Asian Brown Cloud — as it was known earlier — controversy is once again in the news with the Nobel Laureate, Paul Crutzen, and his team of scientists all set to establish two monitoring stations at the Maldives and North Korea to study the `ABC phenomenon'. The two centres will measure the levels and ascertain the exact cause of aerosol and carbon in the atmosphere in the Asian region. They will be set up by October this year.
There are two redirects from atmospheric brown cloud, one leads to this global dimming article and the other one to asian brown cloud. The first redirect should be deleted as the second one is much more specific. --Emil Bild (talk) 14:40, 9 January 2014 (UTC)
Probable causes
We pretty much know the root cause seems to be pollution/aerosols/particulate. We should probably find a picture of a smokestack to move up towards the top. The contrails picture should be towards the bottom since that effect is only secondary.Kgrr16:25, 15 March 2007 (UTC)
The article should get to the point with an image like this one.
The article lacks the explanation that the water droplets are condensing on particulates. As a result, there is an increased amount of reflection of solar radiation back into space, leaving less light to reach the earth. This section still needs to be expandedKgrr21:01, 19 March 2007 (UTC)
Included the new picture of the Golden Gate with the brown cloud in the background. I think it serves the purpose. Expanded the section to include the thoughts on what the root cause is.Kgrr16:24, 11 April 2007 (UTC)
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This article appears to have been substantially written and drawing on evidence from 2005 -2007. There is a significant need to review and re-write this article based in more recent evidence eg
Daniel Rosenfeld, Yannian Zhu, Minghuai Wang, Youtong Zheng, Tom Goren, Shaocai Yu. Aerosol-driven droplet concentrations dominate coverage and water of oceanic low level clouds. Science, 2019; eaav0566 DOI: 10.1126/science.aav0566
This paper for example suggests that Global dimming is increasing, rather than being replaced with ‘global brightening’ as the Wikipedia GD article suggests. Crit scientist (talk) 10:49, 28 December 2019 (UTC)
Quantifying the global cooling effect
The intro says that the effect of global dimming is 0.3-0.7 degrees but it doesn't give a source for the figure. Where is it taken from? --Johannes Rohr (talk) 15:02, 17 January 2020 (UTC)
The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.
Hi InformationToKnowledge. Thanks for nominating this article! I saw on the GAN page that you have been inactive for a few weeks, so I hope all is well with you. I will be reviewing this bit-by-bit. So far I have read the lead and find it nice and clear. I see that there are comments from a previous Good Article Reassessment and will assess whether those issues have been addressed, in addition to the usual checking against GA criteria. Take care, Clayoquot (talk | contribs) 21:50, 23 November 2023 (UTC)
Courtesy notification to GAR reviewers Femke and Chidgk1 that this review is underway. I intend to check whether all of your comments have been addressed and will re-notify you when I've finished checking. Clayoquot (talk | contribs) 20:02, 1 December 2023 (UTC)
Hi InformationToKnowledge, Do you have any thoughts on my comments so far? Everything has been quiet so I am wondering if this review has been helpful so far. If someone intends to work on this in the near future, I will finish my review and will support you to the best of my ability. If not, just let me know. Clayoquot (talk | contribs) 00:18, 15 December 2023 (UTC)
Sorry, I actually didn't realize that you left those comments on the 1st in the first place! I received a ping when you had volunteered to do this review, and I assumed that since the article itself and its talk page are on my watchlist, the GA review would show up in my watchlist as well. Turns out it hasn't, and I have been too preoccupied with Greenland ice sheet this month (most likely my next GA nominee) to check on this page.
This review has certainly been helpful, and now that I am aware of these points, I'll try to address them in the very near future! I just have to get a certain page merge (discussed here) out of the way first, if you don't mind. InformationToKnowledge (talk) 17:53, 15 December 2023 (UTC)
Thank you, and yeah, it seems like we are all slowing down our activity here to celebrate! For now, I acted on one of your suggestions (too much detail regarding cloud interactions) by moving that information to cloud feedback. The rest will have to wait until 2024. InformationToKnowledge (talk) 13:42, 29 December 2023 (UTC)
A. The prose is clear and concise, and the spelling and grammar are correct:
Spelling and grammar are fine, with some exceptions that I'll either describe later or fix myself. I have some concerns about jargon and unclear sentences but before I get into the details of those issues it would be best to address the issues around excessive detail described below. Some unclear content should just be removed.
I have added comments for Criterion 1a in a separate section below.
Unfortunately the lead section is quite far off from the conventions of WP:LEAD. The first sentence should start with "Global dimming is....". There are exceptions to this convention but I think following it here would greatly help the reader.
The first sentence now starts with "Global dimming is...", which is a major improvement. See Femke's comments below regarding readability and lead length.
For layout, the "See also" section needs a deep cleanup.
For words to watch, the weasel words issue raised by Femke seems to have been resolved.
A. It contains a list of all references (sources of information), presented in accordance with the layout style guideline:
B. Reliable sources are cited inline. All content that could reasonably be challenged, except for plot summaries and that which summarizes cited content elsewhere in the article, must be cited no later than the end of the paragraph (or line if the content is not in prose):
Two of the main issues in the 2020 Good Article Reassessment were outdatedness and uncited text. There has been tremendous improvement in these areas. It's good to see a lot of the article being based on the latest IPCC report.
In the Good Article Reassessment, Femke said, "I don't think the geoengineering section is relevant to this article; I've never seen it in that context." The section has since been improved but I don't think the issue of relevance has been addressed. Solar geongineering is a related topic so it deserves a mention. It's currently positioned as if it's an aspect of the topic of global dimming.
The reference you're referring to that relates these concepts is this one, right? I agree the source helps to show the relevance. I'm still concerned about giving wp:undue weight to solar geoengineering - I can get my head around having one paragraph to talk about the relationship between global dimming and solar geoengineering but four paragraphs feels excessive. As Femke raised this issue in the Good Article Review, I'd like to know what she thinks before I sign off on this one.
I think we can find a compromise with the geo-engineering. I believe the last paragraph is a too long for comfortable reading at 170 words (easy-to-read is between 50-100 words, and up to 150 is okay for a majority of readers). That is the paragraph that goes in much too much detail about SRM, way past the "global dimming inspired / gives lessons to" SRM. Can we omit that one, or at least halve it? —Femke 🐦 (talk) 19:54, 11 January 2024 (UTC)
The section on Aircraft contrails has been greatly improved and made more NPOV. Some of this content would be a good addition to Environmental effects of aviation. However, when reading this section I struggle to relate much of what it's saying to the issue of how much sunlight hits the Earth's surface. I would recommend replacing the entire section with one or a few sentences along the lines of "Aircraft contrails contribute to global dimming but they also trap heat emitted by the Earth. Overall, their warming effect is much greater than their cooling effect."
Thanks for condensing this. I'm sorry, I'm really struggling to understand this section.
What is the significance of diurnal temperature variation? When diurnal temperature variation increases as it did in 2001, what does that tell us?
In the sentence However, follow-up studies found that a natural change in cloud cover can more than explain these findings, what findings are explained? Does this sentence mean that all of story from the Sept 11 shutdown is explained by natural causes? If that is the case, why is this story included at all? If it's not the case, what did we learn from the Sept 11 shutdown?
What does "no significant response of diurnal surface air temperature range" mean?
The last paragraph does not seem to be about aircraft contrails at all. It seems to be a list of points in support of the hypothesis that sulfate air pollution has a cooling effect. I'm not sure if this level of detail is important enough to include. If it must be included, it should go with other pieces of evidence that sulfate air pollution has a cooling effect. It should not go in the section about contrails.
The reader should be able to quickly identify what the main scientific claims are and the level of scientific agreement for each of those claims. Throughout the article, I've been struggling to pick out this information, as it's intermixed with details about individual pieces of evidence. To give one example, in the "Relationship to climate change" section, there is a paragraph that gives the range of estimated temperature decreases caused by aerosol cooling, and says While these values are based on combining model estimates with observational constraints, including those on ocean heat content,[47] the matter is not yet fully settled. The difference between model estimates mainly stems from disagreements over the indirect effects of aerosols on clouds.[71][72] This is great. At that point, the article has described a claim and succinctly explained what kind of controversy there is over the claim. The problem (IMHO) is that instead of stopping at that point, the article gives another 343 words about individual studies that have informed the debate. If this article were anywhere other than Wikipedia there would be nothing objectively wrong with those 343 words, but here I feel they are inappropriate uses of primary sources, are distracting from the main points, and should be removed.
Super. The issue of key facts being buried amidst experimental methods and data points is a problem in many places in the article. Can you look for and address as many cases as you can find, and let me know when you're done? Clayoquot (talk | contribs) 20:12, 12 January 2024 (UTC)
File:Xie et al 2022 Asian aerosols.png should be moved to Wikimedia Commons and author information should be stated there as required by the CC-BY license.
FYI I have nominated File:Bomber stream.jpg for deletion on Commons, but it won't affect this GA review. If it gets deleted there, a bot will remove it from all articles.
Thanks for putting a definition in the first sentence of the lead. I think I've gotten my head around the topic but it took me a few reads of this article and some of its sources, plus reading some other sources. To meet Criterion #1a (understandable to an appropriately broad audience), here are some ideas for making things easier to understand:
Use terms consistently
The article seems to use two definitions of "global dimming". In the first definition, global dimming is/was a trend over time. It existed only when each decade was dimmer than the previous, then it ceased to exist in the 1990s. The first definition is used in the lead, "Global dimming was the name given to a decline in the amount of sunlight reaching the Earth's surface, a measure also known as global direct solar irradiance.
In the second definition, global dimming is something that happens whenever there is stuff in the atmosphere that blocks sunlight. Statements such as It is generally believed that the cooling provided by global dimming is similar to the warming derived from atmospheric methane use the second definition.
It is very difficult to make an article understandable when two definitions are in use. What do you think of using the second definition consistently throughout? If I Google "define:global dimming" without quotes most search results seem to use the second definition. The second definition makes much more sense given that stuff continues to be in the atmosphere blocking sunlight.
Here is what the first paragraph of the lead would look like if written to use the second definition consistently:
Global dimming is a decline in the amount of sunlight reaching the Earth's surface, a measure also known as global direct solar irradiance. A dimming trend was observed soon after the first systematic measurements of solar irradiance began in the 1950s, and continued until 1980s, with an observed reduction of 4–5% per decade,[1] even though solar activity did not vary more than the usual at the time.[2][3]
Global dimming is caused by atmospheric particulate matter, predominantly sulfate aerosols. It intensified until around 1990 as a result of rapidly growing air pollution due to post-war industrialization. After 1990, global dimming declined alongside reductions in particulate emissions. This partial reversal of the dimming trend is known as global brightening. Dimming remains more intense than in pre-industrial times.[1] The brightening trend has been globally uneven, as some of the brightening over the developed countries in the 1980s and 1990s had been counteracted by the increased dimming from the industrialization of the developing countries and the expansion of the global shipping industry,[4] although they have also been making rapid progress in cleaning up air pollution in the recent years.[5][6]
Much better. There are still a few places that suggest global dimming no longer exists, e.g. It was observed soon after the first systematic measurements of solar irradiance began in the 1950s, and continued until 1980s and Global dimming had been widely attributed to...Clayoquot (talk | contribs) 23:10, 11 January 2024 (UTC)
When reading a reference work, the reader wants to be able to quickly find facts. The History and Causes sections contain a mixture of facts and myths, which reflects a chronological writing style. Separate the myths about the causes of dimming (solar variability, natural dust, etc.) into a subsection of the "Causes" section. This could be called something like "Alternative hypotheses".
Clayoquot (talk | contribs) 23:28, 23 December 2023 (UTC)
I think such a subheading might backfire by giving an impression of an ongoing debate where there is none. I have rewritten those sections to a fair extent to help address some of the issues. I suppose that the part describing Asian brown cloud and the Maldives might still be problematic - it was one of the few parts left over from the original article that I didn't really touch. InformationToKnowledge (talk) 16:54, 6 January 2024 (UTC)
It's going in the right direction. I moved some of the Maldives stuff to the History section. I see your point about an "Alternative hypotheses" section backfiring; maybe a section like this could be called "Discovery" or "Evidence"? In a reference work where we're trying to make science understandable, what is known about a topic often needs to be presented separately from the tortuous path that humanity took to develop that knowledge. A good example of this is the GA Pneumonia, where there is a Causes section with an overview of causes and sub-sections for each type of cause. The Causes section has almost no descriptions of specific studies or pieces of evidence. The story of how we all learned what we know about pneumonia is told in a History section. Clayoquot (talk | contribs) 23:50, 11 January 2024 (UTC)
Or, instead of having a separate section for Evidence, you could add subsections for individual causes as described below. Then there will be a "Natural emissions" section where you can explain how we know natural emissions are a minor contributor. Clayoquot (talk | contribs) 00:21, 12 January 2024 (UTC)
Minimize duplication / Keep discussion of each cause together
The section called "Past and present", under "Relationship to climate change", is largely repetitive with the Hitory and Causes sections. Duplication needs to be eliminated as much as possible. I suggest moving any points that aren't in the History and Causes section to those sections, and deleting the "Past and present" section altogether.
Before merging these sections, I think it would help to split up the "Causes" section into subheadings such as "Sulfate emissions from humans", "Natural emissions", "Black carbon" and "Aircraft contrails". Clayoquot (talk | contribs) 00:21, 12 January 2024 (UTC)
I don't think splitting sulfate emissions into two is a good idea at all (change in anthropogenic emissions can only be appreciated next to natural emissions staying stable) but I did separate out sulfates and black carbon. The section on contrails had been reorganized entirely. InformationToKnowledge (talk) 19:49, 5 April 2024 (UTC)
Criterion 2c No original research
Here is an example of a statement that seems to be original research: Starting from 2005, scientific papers began to report that after 1990, the global dimming trend had clearly switched to global brightening.[28][39][40][41][42]. If you want to include this kind of statement, you need a secondary or tertiary source that states this directly, i.e. a source that has surveyed the literature from that time period. Quite a few statements in the article are about the history of science around global dimming, rather than being about the science itself. The history of science in this topic area is interesting, but it needs to be written by non-Wikipedians and then summarized by Wikipedians. And there should probably be a lot less of it - in a reference work the reader wants the conclusions of the scientific journey, they don't want the journey. Clayoquot (talk | contribs) 23:42, 23 December 2023 (UTC)
I don't see how to following passage is relevant: In the late 1960s, Mikhail Ivanovich Budyko worked with simple two-dimensional energy-balance climate models to investigate the reflectivity of ice.[25] He found that the ice–albedo feedback created a positive feedback loop in the Earth's climate system. The more snow and ice, the more solar radiation is reflected back into space and hence the colder Earth grows and the more it snows.Clayoquot (talk | contribs) 04:49, 23 December 2023 (UTC)
Thanks for the ping Clayoquot. I think the key improvement still needed is around readability, related to 1a (WP:make technical articles understandable) and 1b (WP:LEADLENGTH). Hemingway says the lead is now written for a post-graduate audience, and I agree. Even though I've studied this as part of my PhD, I struggle with the text (with minor long covid brain fog tbf). Can we reduce the lead length by 1/3 or at a minimun 1/4? Then we'd be on the upper end of a typical lead. And reduce length mostly by reducing sentence length? A few examples of copy-editing for comprehension. ItK, I can strongly recommend the use of large language models in improving readability. The prompt that often works for me is "Can you say X more concisely and simple". :
Instead, global dimming had been attributed to an increase in atmospheric particulate matter, predominantly sulfate aerosols, as the result of rapidly growing air pollution due to post-war industrialization --> Instead, global dimming was due to
After 1980s, reductions in particulate emissions have also caused a "partial" reversal of the dimming trend, which has sometimes been described as a global brightening --> Since the 1980s, a decrease in air pollution has led to a partial reversal of the dimming trend, sometimes referred to as global brightening.
The last superlong sentence of the lead --> The dimming reversal is not complete and varies worldwide. Brightening in developed countries during the 1980s and 1990s was offset by increased dimming in developing countries and by the expansion of the global shipping industry. In recent years, air pollution in developing countries has improved rapidly. (The "they" feels a bit odd here, as if we're assuming the reader is from the global north..)
Thank you for this detailed input and for the link to the Hemingway app. I agree understandability is a problem and these suggestions would help. Clayoquot (talk | contribs) 21:44, 11 January 2024 (UTC)
I did a round of detail-trimming and copyediting of the lead. Got it down to 418 words, which was more than a 1/3 reduction. @InformationToKnowledge: could you please check that I did not make anything inaccurate?
The Hemingway app now says it's at a Grade 13 reading level. @Femke:, when using the Hemingway app I noticed it said there were 11 sentences in the lead. I double-checked and there were 20 sentences. I figured it might be confused by the footnotes so I removed the footnotes, re-ran Hemingway, and it correctly counted 20 sentences. I think the Hemingway app is useful but I don't put a lot of faith in an app that cannot even count sentences. Clayoquot (talk | contribs) 18:45, 13 April 2024 (UTC)
@Clayoquot Thanks! I could never sacrifice those details myself, but I can see how it's better this way. I even removed the sentence about developed/developing countries + shipping, since that detail isn't really any more important than many of the others removed already. With that unwieldy sentence gone, I was able to reorient some sentences to keep the lead back within four paragraphs, which I think is important. InformationToKnowledge (talk) 19:52, 13 April 2024 (UTC)
If you use Wikiwand and copy the lead, Hemingway is not confused. It's annoying that it gets tripped up by the citations for sure. —Femke 🐦 (talk) 19:52, 13 April 2024 (UTC)
See MOS:WEASEL regarding phrases such as Global dimming has primarily been attributed to.... I don't see a reason not to say "Global dimming is primarily caused by...". State facts as if they are facts. Clayoquot (talk | contribs) 19:18, 12 January 2024 (UTC)
In the first image of the "Causes" section, does As it moves through the atmosphere with prevailing winds, weather patterns and seasonality alter these distributions from day-to-day. need to be in the caption? Clayoquot (talk | contribs) 19:38, 12 January 2024 (UTC)
For the first image in the "Relationship to climate change" section, the image says "sulphur dioxide" but the caption says "sulfate aerosols". The caption needs to explain what the relationship is between them. Also "including the cooling provided by sulfate aerosols and the dimming they cause" suggests (erroneously?) that sulfate aerosols provide cooling by another mechanism in addition to dimming. Clayoquot (talk | contribs) 19:44, 12 January 2024 (UTC)
For File:Glantz 2022 Europe aerosols.jpg, after reading the caption several times and looking at the full-size image file, I still cannot figure out what this image is saying. Can you explain in other words 1) what data the image shows, and 2) what the image tells us about global dimming? Clayoquot (talk | contribs) 19:54, 12 January 2024 (UTC)
For File:Smith 2020 SAI RCP scenarios.jpg, I cannot understand this at all. It might help to split the caption into smaller sentences, but it's probably best to formulate a one-paragraph plain-language takeaway and include that instead of the image. If you use the term "Representative Concentration Pathway" you will need to explain what that means. Also spell out SAI. Clayoquot (talk | contribs) 20:00, 12 January 2024 (UTC)
Hi InformationtoKnowledge. I've finally finished a first pass of my review. I will never use GA review templates again - what a pain. To summarize where we are:
The article is scientifically very strong. We are lucky to have someone as knowledgeable as you in our community.
Regarding the GAR, I believe the issues raised there have been either addressed, or were partly addressed and have come up again in this review. Regarding @Chidgk1:'s point that "variation in the radiation emitted by the sun needs to be clearly distinguished from variations in how much is absorbed by the atmosphere", I think the article now does this well.
The main issue is understandability for non-experts. Problems with understandability arise from issues at several levels: Curation (choosing what to leave out), using summary statements, article structure, use of plain language versus jargon, word length, and sentence/length and structure. It is generally easiest to start by removing and summarizing excessive detail, and then moving towards refining the sentences. Let me know how I can help.
Fantastic. When you've addressed as many issues as you can, let me know and I'll give the article a top-to-bottom re-read. I'm aiming to not to re-read individual changes or sections until then, both to save myself time and to avoid becoming too familiar with the content. Cheers, Clayoquot (talk | contribs) 21:45, 15 January 2024 (UTC)
Thanks for the reminder. InformationToKnowledge, do you want to continue with this review? If not, I'll mark it as failed for now but you can re-nominate it at any time if you choose. Clayoquot (talk | contribs) 04:34, 4 March 2024 (UTC)
Yes, for sure! We seem to be really close now: it's just that splitting and reorganizing much of the current article layout into subsections, as you suggested, is a bit of a chore, and a range of higher-view and/or far more problematic articles have blotted out my radar over the past month and a half. (i.e. see the work on Climate change itself, or on Southern Ocean overturning circulation and the other Antarctica-related articles.) I am certainly not abandoning this GA outright, though, and I should be able to set aside enough time for it very soon. InformationToKnowledge (talk) 14:09, 4 March 2024 (UTC)
So, I started to implement some of your suggestions in regards to reorganizing the article (i.e. splitting up the section on causes and moving contrails.) It is still not close to done (i.e. the section on black carbon clearly needs expansion, and I have not yet settled on the best way to address your questions about certain graphics), but it's been an important step forward. InformationToKnowledge (talk) 14:15, 10 March 2024 (UTC)
Apologies, I haven't had time to look at this yet and will need a while longer to dig myself out of my RL to-do list. Thanks for your patience. Clayoquot (talk | contribs) 17:03, 10 April 2024 (UTC)
Ready to pass
This article has come a HUGE way. If there are no objections, I intend to give it a GA rating in the next few days. I did some significant restructuring to the "Relationship to climate change" section so please take a look and make sure I haven't screwed anything up. Thanks InformationToKnowledge for your hard work on this difficult topic! Best, Clayoquot (talk | contribs) 04:31, 14 April 2024 (UTC)
Excellent! I did have to make more than a few changes to your edits, though - mainly to address MOS:SANDWICH which occurred in that section after you moved so many images down and left upper sections without images. I don't quite understand why you did that, but please, don't do it again!
I also added references to the "summary sentences" you made, since any free-standing sentences without references are a magnet for "Citation needed" tags, and with good reason. However, I understand that you wouldn't have had the time to read through the references to select the appropriate ones for those, and fixing it wasn't difficult anyway. I am so ready to finally have this nomination done and to see this article on DYK! (assuming it hasn't been there already, which is unlikely.) InformationToKnowledge (talk) 19:49, 14 April 2024 (UTC)
There are still come open questions in my mind about this article. Nothing major, so not holding up your GA review but it would still be great if someone could take a look and address them. See below on the normal talk page (i.e. not the talk page of the GA review): Overlap with the particulates article, question about image and its caption, better section heading for the solar geoengineering section. EMsmile (talk) 16:09, 15 April 2024 (UTC)
Thanks for catching these issues, InformationToKnowledge, and congratulations on a fine GA! EMsmile, thanks for the reminder of the concerns you brought up earlier, which I trust will be dealt with through the normal editorial process. Clayoquot (talk | contribs) 01:39, 16 April 2024 (UTC)
The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.
^ abCite error: The named reference IPCC_WGI_Ch11 was invoked but never defined (see the help page).
^Cite error: The named reference Eddy et al. 1982 was invoked but never defined (see the help page).
^Cite error: The named reference AGU2021 was invoked but never defined (see the help page).
^Cite error: The named reference Wild2009 was invoked but never defined (see the help page).
^Cite error: The named reference XuRamanathanVictor2018 was invoked but never defined (see the help page).
^Cite error: The named reference Quaas2022 was invoked but never defined (see the help page).
