Global dimming and brightening: A review
Martin Wild
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
There is increasing evidence that the amount of solar radiation incident at the Earth’s surface is not stable over the years but undergoes significant decadal variations. Here I review the evidence for these changes, their magnitude, their possible causes, their representation in climate models, and their potential implications for climate change. The various studies analyzing long-term records of surface radiation measurements suggest a widespread decrease in surface solar radiation between the 1950s and 1980s (“global dimming”), with a partial recovery more recently at many locations (“brightening”). There are also some indications for an “early brightening” in the first part of the 20th century. These variations are in line with independent long-term observations of sunshine duration, diurnal temperature range, pan evaporation, and, more recently, satellite-derived estimates, which add credibility to the existence of these changes and their larger-scale significance.
Current climate models, in general, tend to simulate these decadal variations to a much lesser degree. The origins of these variations are internal to the Earth’s atmosphere and not externally forced by the Sun. Variations are not only found under cloudy but also under cloud-free atmospheres, indicative of an anthropogenic contribution through changes in aerosol emissions governed by economic developments and air pollution regulations. The relative importance of aerosols, clouds, and aerosol-cloud interactions may differ depending on region and pollution level. Highlighted are further potential implications of dimming and brightening for climate change, which may affect global warming, the components and intensity of the hydrological cycle, the carbon cycle, and the cryosphere among other climate elements.
Received 14 November 2008; accepted 10 March 2009; published 27 June 2009.
Citation: Wild, M. (2009), Global dimming and brightening: A review,
J. Geophys. Res., 114, D00D16, doi:10.1029/2008JD011470.
I found this passage that parallels a lot of what I’ve been saying about data quality:
The assessment of the magnitude of these SSR (surface solar radiation) variations faces a number of challenges. One is related to data quality. Surface radiation networks with well-calibrated instrumentation and quality standards as those defined in BSRN [Ohmura et al., 1998] need to be maintained on a long-term basis and if possible expanded into underrepresented regions (see Figure 1b).
However in this figure, citing CRU surface temperature, he likely doesn’t understand what data quality issue might have contributed to the trend from 1960-2000
One of the effects of urbanization is the compression of the diurnal temperature variation. I recently was able to demonstrate this between two stations in Honolulu. One is in the middle of the Airport and had a sensor problem, the other was in a more “rural” setting about 4 miles away. Note how the ASOS station at the airport has an elevated temperature overall, but that the biggest difference occurs in the overnight lows, even when the ASOS sensor giving new record highs was “fixed”:
Urbanization affects Tmin more than Tmax. For example, here’s the nighttime UHI signature of Reno, NV that I drove as a measurement transect using a temperature datalogger:
Click for larger image
Even several hours after sunset, at 11:15PM, the UHI signature remained. The net result of urbanization is that it increases Tmin more than Tmax, and thus minimizes the diurnal range, which we see in Wild’s diurnal range graph.
Even the IPCC misses it:
Wild probably has no idea of this type of issue in the CRU data, but again it speaks to data quality which he seems to be keen on. He’s looking for a global solar signature in temperature data, something Basil Copeland and I have done, to the tune of much criticism. The signature is there, but small. But, when diurnal temperature variation is looked at, any solar signature is likely swamped by the urbanization signal. I’m not saying there is no solar component to what Wild is looking at, but it seems fairly clear that UHI/urbanization/land use change plays a significant role also.
Even rural stations can be affected by our modern society, as Dr. John Christy demonstrated in California’s central valley:
A two-year study of San Joaquin Valley nights found that summer nighttime low temperatures in six counties of California’s Central Valley climbed about 5.5 degrees Fahrenheit (approximately 3.0 C) between 1910 and 2003. The study’s results will be published in the “Journal of Climate.”
The study area included six California counties: Kings, Tulare, Fresno, Madera, Merced and Mariposa.
While nighttime temperatures have risen, there has been no change in summer nighttime temperatures in the adjacent Sierra Nevada mountains. Summer daytime temperatures in the six county area have actually cooled slightly since 1910. Those discrepancies, says Christy, might best be explained by looking at the effects of widespread irrigation.
Wild’s study is a very interesting and informative paper, I highly recommend reading the entire paper here (PDF 1.4 mb)
h/t and sincere thanks to Leif Svalgaard for bringing this paper to my attention.
General suggestion about site:
Have the most recent comment posted at the top rather than the bottom of the list. Will provide a much better flow.
Regards
I remember seeing a BBC documentary years ago on global dimming and how it was masking global warming and how global warming was much worse than anyone taught. It suggested jet contrails were causing cooling but quick bit of research says the opposite.
“Jet Contrails Alter Average Daily Temperature Range”
http://www.sciencedaily.com/releases/2002/08/020808075457.htm
“NASA scientists have found that cirrus clouds, formed by contrails from aircraft engine exhaust, are capable of increasing average surface temperatures enough to account for a warming trend in the United States that occurred between 1975 and 1994.”
ttp://www.sciencedaily.com/releases/2004/04/040428061056.htm
While i am here a bit off topic but interesing also:
http://www.newscientist.com/article/mg20227144.700-sun-leaves-earth-wide-open-to-cosmic-rays.html
The “dimming” hypothesis is central to the claim that models properly simulate the 20th century climate, and thus the attribution of warming to CO2. Aerosols are chosen to have time histories and magnitudes as needed to match the temps in models. Now it likely seems that this alleged canceling factor which “explains” why the warming has been less than models would predict with their high sensitivities, appears to be disappearing…but not accompanied by a ramp up in warming.
Good points about the Diurnal temperature range. The failure of models in this regard is strong evidence that they are failing to account for the influence of land use changes. More over, mean temps that models are supposed to get right are just the average of max and min. If you get the mean right but the max and min wrong, then the “match” is nothing but a COINCIDENCE. Case closed.
Oh my God! That solar irradiance at the surface is out of control, someone call Congress and tell them to turn down the sun!!! (sarcasm off)
If you have the time to waste here is the documentary i refered to in my last comment
There is much that can vary the total amount of solar radiation reaching the ground. Things such as cloud cover and even prevailing winds can locally impact total solar energy reaching the surface.
It shouldn’t be all that difficult to build a sensor array that is responsive to a wide range of wavelengths and simply measure the amount of radiation reaching the sensor. But I would hesitate to extrapolate a local reading into a global proxy. Changes in dust and other particulates, changes in oxides of sulphur, and changes in cloud cover can influence local readings at a specific place but may have no relation to things happening on a global scale.
Now, having finished jabbering, I will go and actually read the paper 🙂
A 20% change in surface radiation from the sun seems significant to me (because I’m no solar scientist). I hope Leif has a few comments on surface radiation.
Two comments:
1. Figure 4 in the paper begs for oceanic and trade wind oscillation analysis. I would bet that correlations can be found. Notice where the trends lay. The paper makes the mistake of averaging surface brightness along arbitrary lines without considering natural weather pattern variation dictated by local and regional trade wind and oceanic oscillations. It would have been better to separate out each area based on the affects of nearby trade wind and oceanic oscillations to sensor location. For example, while the PDO was up and the SOI was down, brightness would be more instructive if separated out into two graphs, that is, measures taken by sensors in and around surface areas affected by the PDO, and surface areas affected by the SOI. Averaging them together potentially covers up important regional weather pattern variation drivers, thus surface radiation, leading to potential false positive or false negative conclusions by the author.
2. Aerosols may be more related to drought and precipitation cycles causing natural atmospheric dust to wax and wane on a decadal scale as a result of oceanic oscillation affects, and less by pollution.
Some here are confusing irradiation with radiance. One is surface solar irradiance of the Sun’s surface as measured by instruments outside Earth’s atmosphere and pointed at the Sun, and demonstrates only tiny variation. The other is surface solar radiance reflected from Earth’s surface through its lower atmosphere as measured by instruments inside Earth’s atmosphere as well as by satellites, pointed at Earth, and thus demonstrates quite a bit of variation. In other words, surface solar irradiance is an exogenous source of variation which is so tiny as to be buried in Earth’s data noise. Surface solar radiance is an endogenous source of variation with a signal that is easily extrapolated from Earth’s data noise.
RE Global dimming on the BBC:
This is an example of how AGW and its obsession on CO2 is killing us.
Treating CO2 as a pollutant, which it is not, has been coming at the expense of reducing real pollutants and toxins.
Mark (11:58:47) :
A 20% change in surface radiation from the sun seems significant to me (because I’m no solar scientist). I hope Leif has a few comments on surface radiation.
What the Sun puts out varies only one in a thousand. What reaches the ground varies a hundred times as much and that variation is thus hardly due to the Sun, which I think is a central point of the paper.
Does anyone know where we can read the actual text of the bill as it was adopted by congress yesterday? Thanks.
Is Doug Hoyt out there? Please comment.
http://www.climateaudit.org/?p=755
Douglas Hoyt:
July 22nd, 2006 at 5:37 am
Measurements of aerosols did not begin in the 1970s. There were measurements before then, but not so well organized. However, there were a number of pyrheliometric measurements made and it is possible to extract aerosol information from them by the method described in:
Hoyt, D. V., 1979. The apparent atmospheric transmission using the pyrheliometric ratioing techniques. Appl. Optics, 18, 2530-2531.
The pyrheliometric ratioing technique is very insensitive to any changes in calibration of the instruments and very sensitive to aerosol changes.
Here are three papers using the technique:
Hoyt, D. V. and C. Frohlich, 1983. Atmospheric transmission at Davos, Switzerland, 1909-1979. Climatic Change, 5, 61-72.
Hoyt, D. V., C. P. Turner, and R. D. Evans, 1980. Trends in atmospheric transmission at three locations in the United States from 1940 to 1977. Mon. Wea. Rev., 108, 1430-1439.
Hoyt, D. V., 1979. Pyrheliometric and circumsolar sky radiation measurements by the Smithsonian Astrophysical Observatory from 1923 to 1954. Tellus, 31, 217-229.
In none of these studies were any long-term trends found in aerosols, although volcanic events show up quite clearly. There are other studies from Belgium, Ireland, and Hawaii that reach the same conclusions. It is significant that Davos shows no trend whereas the IPCC models show it in the area where the greatest changes in aerosols were occurring.
There are earlier aerosol studies by Hand and in other in Monthly Weather Review going back to the 1880s and these studies also show no trends.
So when MacRae (#321) says: “I suspect that both the climate computer models and the input assumptions are not only inadequate, but in some cases key data is completely fabricated – for example, the alleged aerosol data that forces models to show cooling from ~1940 to ~1975. Isn’t it true that there was little or no quality aerosol data collected during 1940-1975, and the modelers simply invented data to force their models to history-match; then they claimed that their models actually reproduced past climate change quite well; and then they claimed they could therefore understand climate systems well enough to confidently predict future catastrophic warming?”, he close to the truth.
_____________________________________________________________________
Douglas Hoyt:
July 22nd, 2006 at 10:37 am
Re #328
“Are you the same D.V. Hoyt who wrote the three referenced papers?” Yes.
“Can you please briefly describe the pyrheliometric technique, and how the historic data samples are obtained?”
The technique uses pyrheliometers to look at the sun on clear days. Measurements are made at air mass 5, 4, 3, and 2. The ratios 4/5, 3/4, and 2/3 are found and averaged. The number gives a relative measure of atmospheric transmission and is insensitive to water vapor amount, ozone, solar extraterrestrial irradiance changes, etc. It is also insensitive to any changes in the calibration of the instruments. The ratioing minimizes the spurious responses leaving only the responses to aerosols.
I have data for about 30 locations worldwide going back to the turn of the century.
Preliminary analysis shows no trend anywhere, except maybe Japan.
There is no funding to do complete checks.
__________________________________________
Leif, thanks for the link to the paper.
Figure 7 in the Wild (2009) paper is telling. It illustrates how well(?) current climate models simulate surface solar radiation. Wild could have saved a lot of time typing Section 5 of his report by answering the question in the section title (How Do Current Climate Models Simulate Global Dimming/Brightening?) with one word: Poorly.
Poorly is also the single-word description of how GCMs model ENSO.
In the concluding remarks, I also found the wording of the first few sentences in paragraph 127 (page 27/31) interesting.
“The origin of dimming/brightening has shown to be
internal to the climate system and not externally forced by
the Sun. The main causes appear to be changes in cloud and
aerosol characteristics and abundance, which MAY OR MAY NOT be microphysically linked. EVIDENCE for an anthropogenic
contribution through emission changes and associated
modification of atmospheric aerosol loads HAS BEEN PRESENTED.” [My caps.]
Not very definite.
A two-year study of San Joaquin Valley nights found that summer nighttime low temperatures in six counties of California’s Central Valley climbed about 5.5 degrees Fahrenheit (approximately 3.0 C) between 1910 and 2003.
It’s a general misconception that Tmin occurs at night. It doesn’t. It typically occurs some time after dawn that varies with season and lattitude.
Jonathan at the blog, a Gust of Hot Air, did detailed analysis of Australian time based temperature data (available for many locations) and found something interesting.
He found that, at most locations, increasing Tmin wasn’t due to increasing nighttime temperatures, but was due to an earlier (in the morning) Tmin.
Something was causing a trend to more early morning warming and it was hard to avoid the conclusion it was less low cloud (near the horizon in the early morning) or less near ground haze, dust or mist.
Which is consistent with the global brightening/dimming analysis above. And points to decreasing industrial and vehicle particulate pollution causing increasing Tmin, and as increasing Tmin is most of the warming in global warming, the phenomena of global warming itself.
Leif:”What the Sun puts out varies only one in a thousand. What reaches the ground varies a hundred times as much and that variation is thus hardly due to the Sun, which I think is a central point of the paper.”
Except of course if it is the sun’s magnetic field’s effect on cosmic rays which cause changes in low level cloudiness. This would put a large gain on the effects of the sun.
I saw that BBC documentary on global dimming as well. There was this climate scientist, Dr Cox (can’t remember from which university) telling viewers that because global dimming was masking the warming effects of CO2, then the AGW temperature sensitivity is actually twice as great as previously thought. No evidence was given for this statement, which went unchallenged by the makers of the film. Dr Cox then produced the current curve of temperature increases as prophesied by the GCM, showing the anomaly of +5 C by 2100, and drew the new corrected line by doubling the original gradient. Result: +10c. Incredibly, this was then followed by a computer generated film showing London rendered under a sub saharan climate, complete with orange dust storms, like a scene from Herbert Spencer;s Dune. Incredibly, the narator then proceeded to warn, in a sombre voice that “this will happen – unless . . .” Note the use of the phrase ‘Will’, not ‘could’, or ‘may’ happen.
Remembering how Global Warming Swindle was attacked for far less, the hypocricy on this stinks.
Allan M R MacRae (13:38:13) :
“So when MacRae (#321) says: “I suspect that both the climate computer models and the input assumptions are not only inadequate, but in some cases key data is completely fabricated – for example, the alleged aerosol data that forces models to show cooling from ~1940 to ~1975. Isn’t it true that there was little or no quality aerosol data collected during 1940-1975, and the modelers simply invented data to force their models to history-match; then they claimed that their models actually reproduced past climate change quite well; and then they claimed they could therefore understand climate systems well enough to confidently predict future catastrophic warming?”, he close to the truth.”
Would you provide proof of your “the modelers simply invented data” claim? For example, show that the sulfate aerosol forcing data that the IPCC AR4 models used was “invented”, by whom, and how.
Extraordinary claims demand extraordinary evidence; please provide some.
I was casually comparing the first chart in the article with this one: click, to see what I could see. Maybe notice a little correlation.
Not a lot of correlation, but the more I looked at the raw data, the more it looks like global warming since the 1950’s is mostly an artifact of data adjustments.
Looking at the illustration for diurnal temperature range (DTR), I am struck by the reduction in the DTR since the 60’s. It suggests to me that the UHI effect is overwhelming data from more pristine rural stations as the number of such rural locations have dramatically dropped off over the years. It says less about the climate and more about the data quality. It seems that this point is also echoed in Dr. Christy’s land use study, which was reported on in 2007, and cited in the article above.
This reminded me of the article of a good station in Tucumcari, NM (rated CRN2) where a warming bias was discovered in the Tmin after 2000, a result of land use change – irrigation.
http://wattsupwiththat.com/2008/06/30/whos-adjusting-the-climate-in-tucumcari-cows-canals-or-hansen/
As the surfacestations project has demonstrated so many times, there’s more to the study of climate than massaging data on a computer; you need lots of field work to validate the data (protesting at a coal-fired electricity generating facility does not constitute field work).
Tom, the bill HR 2454 is available at LOC – http://thomas.loc.gov/cgi-bin/bdquery/D?d111:24:./temp/~bdwaHD:: Click on “Text of Legislation” for the whole monster. Also has related bills, amendments, etc.
Gary Strand (14:48:17) : That aerosol forcings are “pulled out of a hat” to use Hansen’s words is well known. Kiehl (2007) showed that the choice of aerosols forcings to use in 20th century model runs depends on the climate sensitivity… IOW, The data are MADE UP-whatever it takes to get the models to match. Fraud? Value judgment. Fudging? Yes.
http://www.climateaudit.org/?p=2475
http://www.columbia.edu/~jeh1/2009/Copenhagen_20090311.pdf
Leif Svalgaard (16:17:53) :
Mike Borgelt (14:10:16) :
Except of course if it is the sun’s magnetic field’s effect on cosmic rays which cause changes in low level cloudiness. This would put a large gain on the effects of the sun.
Except of course that the cosmic rays and the albedo as measured do not show any significant correlation, and also that cosmic rays to within one percent have been the same at all solar minima we have good data for [since 1951 or so] while the temperature [and presumably the low clouds and the albedo] has not.
The Aerosols forcing data that GISS uses is entirely artificial.
Here it is. [This is the annual data. The monthly Aerosols forcing varies a little bit but since the annual data is so linear, it is clear the monthly data is artificial as well.]
http://img58.imageshack.us/img58/855/modelaerosolsforcingp.png
And this is how Aerosols impacts temperatures (-0.6C as of 2003) compared to the other “forcings” [interesting that forcing and artificial have similar meanings in certain cases].
http://img509.imageshack.us/img509/8388/modeletempimpactst.png
RE first graph (“Fig. 2”), how can a 5-year MA extend beyond the first and last annual observation plotted? There appears to be no annual data before 1923 or after 2000.
A strict 5-year MA would begin and end 2 years inside the end points, though some might reasonably truncate the filter at the ends to give the average of the first and last 3 annual observations. (Michael Mann’s double-flip method would effectively end-peg to the last observation, but even he would not project beyond the last point, I hope.)