In a nutshell, with a −1.6%per decade change in cloud cover during 1954–2005, it becomes a climate forcing. While China is not the world, it bears consideration.
The Hockey Schtick reports:
New paper finds significant, natural decrease in cloudiness over past 50 years
A paper published last week finds that cloud cover over China significantly decreased during the period 1954-2005. This finding is in direct contradiction to the theory of man-made global warming which presumes that warming allegedly from CO2 ‘should’ cause an increase in water vapor and cloudiness. The authors also find the decrease in cloud cover was not related to man-made aerosols, and thus was likely a natural phenomenon, potentially a result of increased solar activity via the Svensmark theory or other mechanisms. As climatologist Dr. Roy Spencer has pointed out his book,
“The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling.”
Ann. Geophys., 30, 573-582, 2012
www.ann-geophys.net/30/573/2012/
doi:10.5194/angeo-30-573-2012
X. Xia
LAGEO, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
================================================================
Abstract:
An updated analysis of cloud cover during 1954–2005 in China was performed using homogeneous cloud cover data from 314 stations. Long-term changes in frequencies of different cloud cover categories and their contributions to long-term changes in cloud cover were assessed. Furthermore, aerosol effects on cloud cover trends were discussed based on comparison of cloud cover trends in polluted and mildly polluted regions. Frequencies of clear sky (cloud cover <20%) and overcast days (cloud cover >80%) were observed to increase by ~2.2 days and decrease by ~3.3 days per decade, respectively, which accounts for ~80% of cloud cover reduction. Larger decreasing trends in cloud cover due to larger increase in clear sky frequency and larger decreases in overcast frequency were observed at stations with lower aerosol optical depth. There is no significant difference in trends regarding cloud cover, clear sky frequency, and overcast frequency between mountain and plain stations. These results are inconsistent with our expectation that larger decreasing trends in cloud cover should have been observed in regions with higher aerosol loading where more aerosols could lead to stronger obscuring effect on ground observation of cloud cover and stronger radiative effect as compared with the mildly polluted regions. Aerosol effect on decreasing cloud cover in China appear not to be supported by this analysis and therefore, further study on this issue is required.
Summary:
A homogeneous cloud cover dataset in China was used to study long-term changes in cloud cover and frequencies of cloud cover categories. A simple yet effective statistical method was applied to study quantitative contributions of graded cloud cover frequency to the overall trend in cloud cover. The relationship between AOD and cloud cover trend was analyzed to discuss aerosol effects on decadal trend of cloud cover. Major conclusions follow.
Significant decline in cloud cover with trend of −1.6%per decade during 1954–2005 was derived. Occurrences of clear sky (cloud cover <20 %) and overcast days (>80 %) were observed to increase and decline by 2.2 days per decade and 3.3 days per decade, respectively. Approximately 80% of overall trend of cloud cover is attributable to an increase in clear-sky days and a decline in overcast days.
Larger decreasing cloud-amount trends have been observed due to larger increasing clear sky frequency and larger decreasing overcast frequency at stations with lower AOD.
There is not significant difference among trends of cloud cover, clear sky frequency, and overcast sky frequency between mountain and plain stations. These analyses do not
support the speculation that the decreasing trend of cloud cover in regions with higher AOD should be larger than that in mildly polluted regions due to stronger aerosol obscuring effect on ground observation of cloud cover and stronger radiative effect in polluted regions. This suggests that causes for significant decreasing trend in cloud cover in China require further study.
Link to the full paper is here: http://www.ann-geophys.net/30/573/2012/angeo-30-573-2012.pdf
Sounds very interesting. As with most climate studies, the error bars are probably huge. -1.6% +/- what?
Solar activity was largest in the middle of the 20th century and has since basically decreased to where it is now down to what it was at the beginning of the 20th century. In spite of this, the cosmic ray intensity has not shown any trend since reliable measurements began in the early 1950s, so it would seem hard to ascribe the decrease in cloud cover to any solar variable.
Bill says:
April 4, 2012 at 2:24 pm
“Sounds very interesting. As with most climate studies, the error bars are probably huge. -1.6% +/- what?”
They use the word “significant” several times; meaning, what they observe is unlikely to happen by chance given the expected error distribution.
Are some of these the weather stations used by Jones in his controversial 1990 and 2008 papers?
http://www.agu.org/pubs/crossref/2008/2008JD009916.shtml
http://www.nature.com/nature/journal/v347/n6289/abs/347169a0.html
http://www.guardian.co.uk/environment/2010/feb/01/dispute-weather-fraud
Hardly surprising: pressures have been steadily rising over the Gobi Desert in China since 1960 and temperatures have been decreasing there during the same period figure 14.47 page 382 Leroux, Dynamic Analysis of Weather and Climate 2010 Springer/Praxis. This confirms once again the insightful analysis by the late French climatologist and of course shows the increase in Mobile Polar Highs reaching deeper southward, hardly a signature of global warming…
Nature can be pretty inconvenient when it wants to.
Just curious, but which measure of “solar activity” are you using to make that statement Leif? And when you state the lack of any cosmic ray trend, which measurement are you referring to? Those aren’t loaded questions, I honestly don’t know the answers and would like to be able to look at the data you are referring to. My reason for asking is because I always thought that cosmic rays were more affected by variations in the strength of the solar wind than by sunspot activity, and I wasn’t sure if there was a good dataset or set of proxies for solar wind going back that far. I also don’t know if the solar wind directly tracks sunspot activity or whether it deviates from direct correlation. With regard to cosmic ray trends, is there a long enough data set from multiple latitudes to determine if there is a difference in trend between higher and lower latitudes?
With regard to the study, I would also want to see if they ruled out large scale vegetation changes due to agricultural use changes. I remember one of the Pielke’s posting a story about the “bunny fence” in Australia and what a difference the vegetation changes made in the cloud cover on each side of the fence.
These analyses do not
support the speculation that the decreasing trend of cloud cover in regions with higher AOD should be larger than that in mildly polluted regions due to stronger aerosol obscuring effect on ground observation of cloud cover and stronger radiative effect in polluted regions.
A peculiar hypothesis. Its well established that aerosols seed clouds (and its a large effect) so one would expect higher cloud cover levels where AOD is high. I’d be surprised if the obscuring ground observation effect of aerosols was larger.
Otherwise its unfortunate that they do not relate cloud cover changes to aerosol changes. I would not make the assumption that high aerosol areas are areas where aerosol levels have increased over the period of the study. Aerosol level changes in China is a complex picture with likely decreasing particulates and black carbon, while SO2/NO2 has increased.
The aerosol picture in most of the rest of the world is very different to China. So I wouldn’t draw any global conclusions from this.
How will China support their indigenous work within the IPCC political circus?
Leif Svalgaard says: April 4, 2012 at 2:40 pm
“Solar activity was largest in the middle of the 20th century and has since basically decreased”
As usually, Leif trys to mislead the readers of this blog.
The truth is that there is a debate about what the sun did during the last 50 years. There is an agreement that the sun dereased its activity from 1940-1950 to 1970. From 1970 to 2000 solar acticity is claimed by PMODto have been remained constant or slighly decreased.
However the ACRIM group claims otherwise and the solar irradiance increased from 1970 to 2000, and now is decreasing.
Everything is clearly explained here
http://acrim.com/TSI%20Monitoring.htm
Leif knows very well that there exists a controversy about this issue, but he is not interested in fairly present the issues. Leif also forget to mention that PMOD composite is based on a manipulation of some satellite records. See here
http://climatechange.thinkaboutit.eu/scripts/tinymce/jscripts/tiny_mce/plugins/imagemanager/files/Kremlik/Hoyt.jpg
The above finding about a cloud cover decreasing from 1970 to 2000 due to a 60-year astronomical/solar during its warming phase is perfectly consistent with the findings of my papers where also the cloud connection is discussed. For example
N. Scafetta, “A shared frequency set between the historical mid-latitude aurora records and the global surface temperature” Journal of Atmospheric and Solar-Terrestrial Physics 74, 145-163 (2011). DOI: 10.1016/j.jastp.2011.10.013.
N. Scafetta, “Multi-scale harmonic model for solar and climate cyclical variation throughout the Holocene based on Jupiter-Saturn tidal frequencies plus the 11-year solar dynamo cycle.” Journal of Atmospheric and Solar-Terrestrial Physics in press (2012).
So, we have more data contraddicting AGW advocates and Leif.
http://members.optusnet.com.au/~gradds55/solar.jpg
Where does this fit in? .. seems to back Nicola’s description of heightened solar activity in the latter part of the 20th century.
Time to revisit this:
http://wattsupwiththat.com/2007/10/17/earths-albedo-tells-a-interesting-story/
This was 2007. It has further increased or remained about the same (from what I’ve found) in the meantime. The figure is key — note the relative forcing compared to the combined GHG forcing (whatever “forcing” ultimately means in a detailed balance equation). Personally, I prefer the variation in the greybody temperature, which takes into account albedo.
To Leif:
IIRC, both the solar magnetic field and the Earth’s magnetic field fluctuate, and both affect cosmic ray counts. Polar stations e.g. Oulu do show significant increases in neutron counts since e.g. the early 80’s (~25%), do they not (which is more likely to be associated with solar fields). But as the Earth’s magnetic pole wanders and the Earth’s field fluctuates, might that not modulate cosmic ray counts as well, quite possibly in tropical regions with a differential impact on climate?
Either way, whatever the cause the Earth’s albedo appears to have significantly increased over the last 15 years. Given a baseline albedo in the ballpark of 0.3, 7% is around 0.02 variation from 1997 to the present. That corresponds to roughly 2 degrees K variation in the baseline greybody temperature before the GHE goes into effect to raise it. Note also that the decrease in albedo from 1985-1986 to 1997 almost precisely corresponds to the timeframe (and, lagged, the magnitude) of the “unexplained” temperature increase of that period, the part that was attributed to climate sensitivity on top of the GHE increase (which by itself is much smaller).
This explains — or “can” explain — why even serious climate scientists might have been mistaken about climate sensitivity. The very period where the IPCC was “stimulated” by Mann’s hockey stick in 1998 on began right at the end of a period where the albedo had dropped by 10 percent! over fifteen or twenty years, a drop that was interpreted (correctly or not) as being due to climate sensitivity — an increase in atmospheric humidity and decrease in cloud cover due to increase greenhouse forcing. According to this, however, this process should continue unabated as long as GHGs increase, leading to egregious estimates of the feedback. Note that 10% corresponds to almost 3K increased forcing all by itself (but we didn’t see all of it because it is lagged by years to decades).
However, the subsequent increase in albedo by 7% (which we can also expect to be lagged by years to decades in its effect on mean temperature) is completely unexplainable in terms of this forcing model. It directly confounds the actual physical basis of the presumed high climate sensitivity, and worse — suggests that by far the majority of the late 20th century warming was due to modulation of albedo, not modulation of CO_2.
Svensmark provides an appealing hypothesis to explain why there appears to be some connection between solar state and global temperature. However, one does not need to engage in this debate to look at the albedo data and connect it to expected global temperature. Whatever the mechanism responsible for the modulation, the modulation exists, behold it. It is not only significant, it is many times larger than the expected effect resulting from anthropogenic modulation of CO_2. It is, in fact, one of the relatively few mechanisms proposed (aside from chaos and self-organization of major heat transport mechanisms) that can explain the observed variability of global temperatures over the Holocene.
In a sane Universe, physicists and climatologists would be busting their butts to understand the 10% variability in albedo, given its primary role in thermoregulation. Instead it happens, and then everybody forgets it. It is the omitted variable — one cannot even argue that it should or shouldn’t be present, and using a constant value over decadal timescales is manifestly a mistake. Garbage in, garbage out.
rgb
Finding an explanation for this 1-2% cloud cover change will only result from application of numerous hypotheses, being tested in parallel, over some goodly periods of time. My best guess, all the likely effects in some non linear and chaotic combination.
Leif says “… In spite of this, the cosmic ray intensity has not shown any trend since reliable measurements began in the early 1950s …”
Any trend is a large and unknown list. Is is just that no one has been able to find a trend so far? Has someone looked for a trend of CRI integrated over solar cycles?
Good for Robert Brown: Whether or not researchers adduce the cause of Earth’s “significantly increased” albedo since about 1997, the fact remains that heightened reflectivity must result in a consistent cooling trend. Cloud cover, sea-ice extent, whatever… odd indeed that legions of data-junkies simply ignore a major influence on near-term global temperature conditions.
Dr. Spencer, if you haven’t seen this, you should check it out. Damped summer warming accompanied with cloud cover increase over Eurasia from 1982 to 2009 It’s a new paper out in Environmental Research Letters……
I just finished reading it and posting on my blog, when I popped my head up and see your conversation. It’s really a pretty lame paper……. they do make a huge finding though…… the areas where clouds are in the summertime correlates well with “dampened warming”. And, it seems things get hotter without them as well!!! This study was only conducted in Eurasia…… no word about how clouds would effect the rest of the world’s summertime temps. …….
Honest question about GCR measurements….
If GCR do catalyse cloud seed formation a la Svensmark, wouldnt they subsequently fail to reach ground based measurement locations?
Put another way, if GCR’s are ‘used up’ making clouds, would that diminnish the signal recieved at ground measurement stations?
Robert Brown says:
April 4, 2012 at 4:36 pm
Time to revisit this:
http://wattsupwiththat.com/2007/10/17/earths-albedo-tells-a-interesting-story/
The Earthshine project continues. This link has a graph up to 2008 which shows the albedo increase from around 1997 continues.
http://www.bbso.njit.edu/Research/EarthShine/
The pre-1997 decline in albedo can be explained by decreasing global anthropogenic aerosol levels (clouds seeded by them), but the post 1997 rise is something of a puzzle. A possible explanation is that while global aerosol levels were steady during this period. They increased over tropical and subtropical Asia, while decreasing at higher latitudes. Resulting in more tropical and subtropical clouds and more reflected sunlight from lower latitudes.
Don’t forget the early spring in the U.S. midwest; the trees, shrubs and plants are nearly in full bloom, one month early.
With all that shade, the ground warms slower.
I think the theory expects a decrease in cloud cover.
The sunlight reflecting nature of cloud cover Albedo (about -53.0 W/m2) outweighs the back-radiation greenhouse effect of clouds (about +32.0 W/m2).
The theory is based on a feedback effect of +1.0 W/m2 per 1.0C increase in temperatures (signalling that cloud cover will decline by up to 5% given its net impact of -21.0 W/m2 even though humidity is expected to increase by 7.0% per 1.0C increase in temperatures and the climate modelers sometimes say they expect a 2.0% increase in cloud cover.
In reality, cloud cover is the make or break feedback effect. Humidity is based on the reasonably solid Classius Clayperon relation while cloud cover is just a guess at best.
If the cloud cover feedback is -1.0 W/m2/1.0C rather than +1.0 W/m2/C, then the CO2 sensitivity falls to 1.5C or so per doubling. The multiplier effect. Technically, I’ve always assumed this feedback effect has been tuned to deliver 3.0C per doubling since the climate models cannot actually determine what feedback clouds will deliver. +/- 1.0 W/m2/1.0C is a make or break factor. They picked 3.0C long ago and they are sticking with it.
(And humidity is not actually increasing according to the Classius Clayperon equations either. It is as flat as a board over the long term with the ENSO running its +/- level apparently).
http://img577.imageshack.us/img577/4600/watervapouripccvsreanal.png
http://img52.imageshack.us/img52/5716/ensotempsvstcwvnov11.png
Lief Svalguard says: …. “Solar activity was largest in the middle of the 20th century and has since basically decreased to where it is now down to what it was at the beginning of the 20th century. In spite of this, the cosmic ray intensity has not shown any trend since reliable measurements began in the early 1950s, so it would seem hard to ascribe the decrease in cloud cover to any solar variable.”
Unless you are dealing with a “threshold” system, wherein solar activity reaches a threshold at which no more significant cosmic ray can penetrate. If such, then you’d probably have to go back further than 1950, as I recall, what was it, .. cylce 19, was the peak. Looking at the Butterfly graph of sunspot area, there appears to be a near constant intensity since cycle 18 up until cycle 24. In fact, it looks pretty flat since 1940, as cycle 18 was looks to be approximately equal in magnitude to cylces 21 and 22, and to some degree, even cycle 23. The only dwarf is cycle 20. .. and of course, cycle 24.
Robert Brown wrote (April 4, 2012 at 4:36 pm): “In a sane Universe, physicists and climatologists would be busting their butts to understand the 10% variability in albedo, given its primary role in thermoregulation. Instead it happens, and then everybody forgets it. It is the omitted variable — one cannot even argue that it should or shouldn’t be present, and using a constant value over decadal timescales is manifestly a mistake. Garbage in, garbage out.”
Piers Corbyn (late 2011 in Germany):
rgb: In a sane Universe, physicists and climatologists would be busting their butts to understand the 10% variability in albedo, given its primary role in thermoregulation. Instead it happens, and then everybody forgets it. It is the omitted variable — one cannot even argue that it should or shouldn’t be present, and using a constant value over decadal timescales is manifestly a mistake.
A good comment.
Bill Illis’ (April 4, 2012 at 6:21 pm) water vapor / ENSO graph:
http://img52.imageshack.us/img52/5716/ensotempsvstcwvnov11.png
Thanks for relentlessly reminding everyone Bill.
“Apart from all other reasons, the parameters of the geoid depend on the distribution of water over the planetary surface.” — N.S. Sidorenkov