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.
For those who haven’t seen the documentary on Henrik Svensmark’s finding on aerosols and cosmic rays here is the first of a five part YouTube series.
Leif Svalgaard (17:06:48) :
Leif Svalgaard (16:21:13) :
perhaps a nice moderator would just FIX this…
Ah, well, he didn’t…
[Reply: Please be more specific, Leif. What exactly would you like fixed? ~ dbstealey, moderator]
That Leif Svalgaard (16:17:53) : be changed as shown below
and that
Leif Svalgaard (16:18:43) :
Leif Svalgaard (16:21:13) :
Leif Svalgaard (17:06:48) :
be removed, thanks.
———————————-
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.
[Reply: Done. ~dbs]
I wonder what would happen if the forcing from the brightening/dimming on global temps. was removed from the record, would we have less amount of a warming trend over the 20th century?
Meanwhile we’re just getting over our first extended heatwave here, the amazing part is that out of 5 days here in Wichita they were predicting to hit or pass 100 degrees, we only had one 100 degree day as temps. fell short of the forecast and hit 97-99 degrees instead. In fact total no. of stations with 100 degree readings in Kansas seemed to be a bit less than what was forecast, maybe partly thank the Sun which it seems to be dimming and not because of pollution. 🙂
Leif Svalgaard (17:43:07) :
[Reply: Done. ~dbs]
thanks, and then remove 17:43:07 and this one too.
hot off the press regarding Jim Hansen
http://epw.senate.gov/public/index.cfm?FuseAction=Minority.Blogs&ContentRecord_id=1a5e6e32-802a-23ad-40ed-ecd53cd3d320
Tim (18:03:46) : hot off the press regarding Jim Hansen
I don’t think that an entry from January 27, 2009 is “Hot Off the Press”.
Dr. Theon being a skeptic and his comments about Hansen are old hat by now.
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.”
Except of course we can experimentally test short term correlations say with Forbush decreases.
Pudovkin, M. I. and Veretenenko, S. V.: Cloudiness decreases associated with Forbush decreases of galactic cosmic rays, J. Atmos. Sol.-Terr. Phy., 57, 1349–1355, 1995.
Tim (18:03:46) :
Hot off the press? January 27th?
OT, but being as Adam from Kansas (17:55:41) was not snipped:
June 27, 2009 San Antonio Express-News
The lingering heat wave on Friday obliterated a high temperature record that had stood since 1980.
The 103 reading surpassed the 102 mark set 29 years ago, according to the National Weather Service, which predicts similar readings at least through Sunday.
Authorities said more than 80 people have been treated for heat-related illnesses so far in June around San Antonio, where temperatures have reached 100 degrees nine times this month, but no heat-related deaths have been reported.
maksimovich (18:43:52) :
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.”
Except of course we can experimentally test short term correlations say with Forbush decreases.
Pudovkin, M. I. and Veretenenko, S. V.: Cloudiness decreases associated with Forbush decreases of galactic cosmic rays, J. Atmos. Sol.-Terr. Phy., 57, 1349–1355, 1995.
and when we do [note publication date 2008]:
Cosmic rays, cloud condensation nuclei and clouds – a reassessment using MODIS data
Kristjánsson, J. E. et al.
Atmospheric Chemistry and Physics, Volume 8, Issue 24, 2008, pp.7373-7387
The response of clouds to sudden decreases in the flux of galactic cosmic rays (GCR) – Forbush decrease events – has been investigated using cloud products from the space-borne MODIS instrument, which has been in operation since 2000. By focusing on pristine Southern Hemisphere ocean regions we examine areas where we believe that a cosmic ray signal should be easier to detect than elsewhere. While previous studies have mainly considered cloud cover, the high spatial and spectral resolution of MODIS allows for a more thorough study of microphysical parameters such as cloud droplet size, cloud water content and cloud optical depth, in addition to cloud cover. Averaging the results from the 22 Forbush decrease events that were considered, no statistically significant correlations were found between any of the four cloud parameters and GCR, when autocorrelations were taken into account. […]
Confident as ever Leif. David Stockwell looked into that paper and said that he thinks that the paper is “schizophrenic”:
http://landshape.org/enm/cosmic-rays-cloud-condensation-nuclei-and-clouds-%E2%80%93-a-reassessment-using-modi-data/
Because their claims of “insignificance” appear to be belied by their own tables etc.
But such a limited study can hardly be used to definitively reach such broad conclusions. I know you are skeptical of most solar-climate stuff, but you might want to avoid jumping on papers that reinforce those perceptions!
Does anybody know this: Assuming Svensmark is correct and Cosmic ray burst etc are distributed equally over the hemisphere, there should be a correlation between clouds and cosmic ray count? Maybe the bursts hit some areas more than other? In this case hard to correlate? Hasn’t this been done?
Re Svensmark Sorry just saw previous post question answered. What a coincidence!
Leif,
From my reading not all GCRs are equal. Svensmark does address the issue of Forbush events in his work. He indicates that the events are short lived and often not powerful enough to deflect muons. I do not feel that a study based on Forbush events is sufficient to dismiss the GCR/cloud hypothesis. The CLOUD experiment is designed to look at the interaction of muons, near ocean surface air chemistry and UV radiation. I believe that the controlled experiment at CERN is most appropriate way to investigate this matter. I am wary of attempts to dismiss the hypothesis through computer modelling or observations during Forbush events of limited duration and variable effect. For better answers we will just have to wait on results from the physical experiment.
Having said that, I would not be surprised if the role of muons in cloud nucleation turns out to be just one of Jack Eddy’s “many plugs”.
timetochooseagain (19:50:06) :
Because their claims of “insignificance” appear to be belied by their own tables etc.
What this just shows is that it has not been established that there is a significant correlation. You don’t see papers anymore trying to show that geomagnetic storms come from the Sun. That is because that has been established.
Konrad (20:58:33) :
From my reading not all GCRs are equal. Svensmark does address the issue of Forbush events in his work. He indicates that the events are short lived and often not powerful enough to deflect muons.
maksimovich (18:43:52) was using Forbush events to ‘test’ the stuff. doesn’t this cut both ways? Or maybe not: if something supports a hypothesis it is good, if it does not, then it is ‘not powerful enough’.
Muons are created in the atmosphere and are not ‘deflected’.
I’m not saying that there is no effect. What I’m saying is that it has not been established that there is an effect. Anybody is free to speculate as he/she wants, as long as it is labeled as such. But, the GCR effect has almost become as much dogma as AGW, just with the opposite sign.
Instead of looking for correlations, one can try to use physics to address the efficiency of the process of GCRs:
Can cosmic rays affect cloud condensation nuclei by altering new particle formation rates?
Pierce, J. R.; Adams, P. J.
Geophysical Research Letters, Volume 36, Issue 9, CiteID L09820, 05/2009
“Although controversial, many observations have suggested that low-level cloud cover correlates with the cosmic ray flux. Because galactic cosmic rays have likely decreased in intensity over the last century, this hypothesis, if true, could partly explain 20th century warming, thereby upsetting the consensus view that greenhouse-gas forcing has caused most of the warming. The “ion-aerosol clear-air” hypothesis suggests that increased cosmic rays cause increases in new-particle formation, cloud condensation nuclei concentrations (CCN), and cloud cover. In this paper, we present the first calculations of the magnitude of the ion-aerosol clear-air mechanism using a general circulation model with online aerosol microphysics. In our simulations, changes in CCN from changes in cosmic rays during a solar cycle are two orders of magnitude too small to account for the observed changes in cloud properties; consequently, we conclude that the hypothesized effect is too small to play a significant role in current climate change.”
—————
I know that people will shout MODEL only, thus LIES. But read the paper and see that this is a different [good] kind of model, i.e. not the climate models that pretend to forecast a hundred years ahead the effect of a butterfly beating its wings.
Anyway, I have not seen a convincing demonstration of the GCRs being a significant climate driver. Not that there are not many claims of that. It is almost so that the more claims there are, the less likely it is that they are true. [why keep trying to show that something is true when it has already been established?]
When I grew up in Sacramento, the largest common diurnal range was 45 degrees.
I was a bit shocked to see older records in a rural area topping 60 degrees diurnal range.
The change happened over a period of twenty years or so. Well before WWII.
Leif Svalgaard (19:31:38) :
“and when we do [note publication date 2008]:
Cosmic rays, cloud condensation nuclei and clouds – a reassessment using MODIS data
Kristjánsson, J. E. et al.
Atmospheric Chemistry and Physics, Volume 8, Issue 24, 2008, pp.7373-7387 ”
Yes I thought you would use that argument,hence use of way back machine and how Pudovkin has withstood the test of time eg
SOLAR ACTIVITY, COSMIC RAYS AND CLIMATE CHANGE
(ON THE 75TH ANNIVERSARY AND IN MEMORY OF PROF. M.I. PUDOVKIN )
O.M. Raspopov, S.V. Veretenenko 2009
Abstract. A review of the research activity of M.I.Pudovkin, his co-workers and followers in solving the problem of the solar activity influence on atmospheric processes and climate change is presented, the roles of cosmic ray variations and changes in cloudiness are emphasized. The problems that still remain unresolved in this field are outlined.
Kristjansson um tends to overlook his eastern neighbours hence he is able to use ” average”assumptions eg
‘Averaging the results from the 22 Forbush decrease events that were considered,
no statistically significant correlations were found between any of the four cloud parameters and GCR, when autocorrelations were taken into account.’
Linear approximation in a non-linear world eg
Empirical evidence for a nonlinear effect of galactic cosmic rays on clouds 2006
BY R. GILES HARRISON* AND DAVID B. STEPHENSON
Galactic cosmic ray (GCR) changes have been suggested to affect weather and climate, and new evidence is presented here directly linking GCRs with clouds. Clouds increase the diffuse solar radiation, measured continuously at UK surface meteorological sites since 1947. The ratio of diffuse to total solar radiation—the diffuse fraction (DF)—is used to infer cloud, and is compared with the daily mean neutron count rate measured at Climax, Colorado from 1951–2000, which provides a globally representative indicator of cosmic rays. Across the UK, on days of high cosmic ray flux (above 3600!102 neutron counts hK1, which occur 87% of the time on average) compared with low cosmic ray flux, (i) the chance of an overcast day increases by (19G4) %, and (ii) the diffuse fraction increases by
(2G0.3) %. During sudden transient reductions in cosmic rays (e.g. Forbush events),
simultaneous decreases occur in the diffuse fraction. The diffuse radiation changes are, therefore, unambiguously due to cosmic rays. Although the statistically significant nonlinear cosmic ray effect is small, it will have a considerably larger aggregate effect on longer timescale (e.g. centennial) climate variations when day-to-day variability averages out.
An important aspect of this is the dynamical aspects say in solar eg A. N. Gruzdev et al.: Effect of solar rotational variation on the atmosphere 2009
“In the extratropical latitudes, the responses are, in general,seasonally dependent. The sensitivity is in many cases stronger in winter than in summer. This has also been observed e.g. by Ruzmaikin et al. (2007) and is a hint to a possible
dynamical response to 27-day solar forcing. To clearly identify such a response, further analysis is needed.
Experiments with different forcing amplitudes have shown that the responses of temperature and of the concentrations of chemical species to 27-day forcing are non-linear. Their sensitivities (not amplitudes) generally decrease when the forcing
increases. This conclusion is important to understand the possible differences of observational studies obtained at times of different forcing amplitudes.”
Which allows us to return to FD attenuation(note publication 2009)
The effects of Forbush decreases on Antarctic climate variability: a
re-assessment
B. A. Laken and D. R. Kniveton
Abstract
In an attempt to test the validity of a relationship between Galactic cosmic rays (GCRs) and cloud cover, a range of past studies have performed composite analysis based around Forbush decrease (FD) events. These studies have produced a range of conflicting results, consequently reducing confidence in the existence of a GCR-cloud link.
A potential reason why past FD based studies have failed to identify a consistent relationship may be that the FD events themselves are too poorly defined, and require calibration prior to analysis. Drawing from an initial sample of 48 FD events taken from multiple studies this work attempts to isolate a GCR decrease of greater magnitude and coherence than has been demonstrated by past studies. After this calibration composite analysis revealed increases in high level (10–180 mb) cloud cover (of 20%) occurred over the Antarctic plateau in conjunction with decreases in the rate of GCR flux during austral winter (these results are broadly opposite to those of past studies).The cloud changes occurred in conjunction with locally significant surface level air temperature increases over the Antarctic plateau (4 K) and temperature decreases over the Ross Ice Sheet (8 K). These temperature variations appear to be indirectly linked to cloud via anomalous surface level winds rather than a direct radiative forcing. These results provide good evidence of a relationship between daily timescale GCR variations and Antarctic climate variability.
maksimovich (21:55:35)
(Memo to self include links)
http://www.atmos-chem-phys-discuss.net/9/10575/2009/
The effect of the solar rotational irradiance variation on the middle
and upper atmosphere calculated by a three-dimensional
chemistry-climate model
A. N. Gruzdev1, H. Schmidt2, and G. P. Brasseur3
http://www.atmos-chem-phys.net/9/595/2009/
One important note is the FD and say 27 day rotation allow us to “test” the qualities of the science in shorter time scales,and if we can see various “mechanisms” at work.
maksimovich (21:55:35) :
Yes I thought you would use that argument,hence use of way back machine and how Pudovkin has withstood the test of time eg…
As I said, there is no lack of claims and counterclaims.
Leif,
Yes I stand corrected, muons are created within the atmosphere. Svensmark actually was referring to the limited ability of some Forbush events to deflect muon creating particles (page 206 The Chilling Stars.) The ambiguity and variability of results from studies involving Forbush events seems to confirm Svensmark’s claim that cloud observations during these events are unlikely to prove or disprove the hypothesis.
Like yourself, I would say that I have not yet seen a convincing demonstration of GCR flux driving climate. I do not know if Svensmark is right. I do know he is doing the right thing in conducting physical experiments. Are those dismissing the hypothesis using Forbush studies or computer modeling prior to the results of a high quality physical experiment doing the right thing?
Well, Leif, the summer here in Greece so far reminds me of month October…rain, clouds & cold that were unseen around this area before.
So because solar radiation has been decreasing since about 1945, does this discredit the theory that the sun has had anything to do with earth’s global warming for the last 65 years?
Konrad (22:38:36) :
Are those dismissing the hypothesis using Forbush studies or computer modeling prior to the results of a high quality physical experiment doing the right thing?
Are the ones that use Forbush studies in support of the hypothesis doing the right thing? In both cases I would say “yes”, because the are many facets to this and it pays to look at them. It is not clear to what degree the ‘high quality’ experiment will be even applicable. I’m sure if it turns out negative that the supporters will claim that perhaps this was not a good test after all because of the difference of scale or some such.
the_Butcher (22:43:27) :
Well, Leif, the summer here in Greece so far reminds me of month October…rain, clouds & cold that were unseen around this area before.
Perhaps wearing a tin-hat to protect against cosmic rays may keep your brain from freezing up 🙂