A new paper just published in the Journal of Climate finds that global cloudiness has decreased over the past 39 years from between 0.9 to 2.8% by continent as shown in the figure below:
DJF. Continental seasonal anomalies are based on seasonal station anomalies averaged within 10˚ grid
boxes, which are then averaged over the continent weighted by land fraction and box size. Interannual
variation (IAV) is the standard deviation of the time series. Trends are determined using the median of
pairwise slopes method.
The period of the study is from 1971 to 2009. The authors say that:
“Global average trends of cloud cover suggest a small decline in total cloud cover, on the order of 0.4% per decade.”
Taken together, global cloud cover decreased and average of 1.56% over this 39 year period. WUWT readers may recall that Dr. Roy Spencer points out the issue of a slight change in cloud cover in his 2010 book intro of The Great Global Warming Blunder: How Mother Nature Fooled the World’s Top Climate Scientists. He writes:
“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.”
So there you have it, by the work of independent scientists, it is suggested that Dr. Spencer’s hypothesis of just a small change (1-2%) of cloud cover has been observed in their study. This can account for the global warming changes observed. Cloud cover has decreased over the past 39 years globally, and temperatures have risen during that time. This global decrease in cloud cover alone could account for all surface warming observed since the 1970’s. Interestingly, some types of clouds have been on the increase, while others have been on the decrease. Figure 2 shows this:
40˚-80˚N, and 20˚-180˚ E. Anomalies are calculated for individual stations, then averaged within 10˚
equal-area grid boxes, box values are averaged over the entire area, weighted by box size and land
fraction in each box.
Now, a cause needs to be identified as to why some clouds increase and others decrease. One of the obvious ones to examine is Svensmark’s cosmic ray hypothesis, which says that as solar (magnetic) activity decreases, cosmic ray insolation intensity increases, and cloud cover increases due to more cosmic ray seeding. Aerosols and ENSO may also figure greatly in cloud formation changes. It will be a tough puzzle to fully disentangle given that there have been a number of stations lost that record cloud cover type and the move has been towards automated systems (like ASOS) which only record cloud height and not type. The data in this study is mostly from human observers noting cloud type and height for aviation purposes. Perhaps there will be a way to get this information as the number of observers decrease from satellite image processing.
Here’s the paper:
Ryan Eastman and Stephen G. Warren
Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195 Journal of Climate 2012: http://dx.doi.org/10.1175/JCLI-D-12-00280.1
Abstract
An archive of land-based, surface-observed cloud reports has been updated and now spans 39 years from 1971 through 2009. Cloud-type information at weather stations is available in individual reports or in long-term, seasonal, and monthly averages. A shift to a new data source and the automation of cloud reporting in some countries has reduced the number of available stations; however this dataset still represents most of the global land area.
Global average trends of cloud cover suggest a small decline in total cloud cover, on the order of 0.4% per decade. Declining clouds in middle latitudes at high and middle levels appear responsible for this trend. An analysis of zonal cloud cover changes suggests poleward shifts of the jet streams in both hemispheres. The observed displacement agrees with other studies.
Changes seen in cloud types associated with the Indian monsoon are consistent with previous work suggesting that increased pollution (black carbon) may be affecting monsoonal precipitation, causing drought in North India. A similar analysis over northern China does not show an obvious aerosol connection.
Past reports claiming a shift from stratiform to cumuliform cloud types over Russia were apparently partially based on spurious data. When the faulty stations are removed, a tradeoff of stratiform and cumuliform cloud cover is still observed, but muted, over much of northern Eurasia.
====================================
The full paper is available on the author’s website:
http://www.atmos.washington.edu/~rmeast/Full_Text_D1.pdf
Dr. Spencer’s book is available from Amazon:
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Cloud cover has decreased over the past 39 years globally, and temperatures have risen during that time. This global decrease in cloud cover alone could account for all surface warming observed since the 1970′s. Now, a cause needs to be identified. One of the obvious ones to examine is Svensmark’s cosmic ray hypothesis.
Except that as solar activity has generally decreased [hence cosmic ray intensity increased], Svensmark’s hypothesis would predict an increase in cloud cover. So, no need to look there.
REPLY: I know you would like to dismiss Svensmark out of hand, and I should have been clearer. There are some indications in the paper that certain types of clouds have in fact been on the increase while others are on the decrease. See figure 2 for example. Cumulonimbus has been on the increase while Nimbostratus has been on the decrease. I’ll add that figure. Like I said disentangling it all will be a challenge. – Anthony
Interesting. Correct me if I mis-remember, but doesn’t one of the foundations of CAGW suggest that as it warms there will be less cloud and thus less rain? No references, just a hazy recollection.
What I think now becomes important is what comes first – less cloud due to natural variation forcing temperature rise; or temperature rise due to the dastardly CO2 forcing less cloud. And at what point do the feedbacks (from either side of the argument) kick in?
” Now, a cause needs to be identified. ”
Let me think what the warming crowd will come up with as the definitive answer ?
Positive cloud feedback
Everyone knows that it’s the tons of evil CO2 that humans release that is actually crowding out the clouds. Duh!
/sarc
Its reduced anthropogenic aerosol cloud seeding.
All we need to do to fix the climate is get rid of pollution controls on motor vehicles and coal fired power stations, and stop trying to put out forest fires.
The Greenies aint going to be happy.
On a more serious note, I just posted this link on geo-engineering thread, which indicates biomass burning is the main cause of anthropogenic cloud seeding.
http://www.agu.org/pubs/crossref/2007/2006JD008269.shtml
I would be very careful about drawing conclusions as to the directions of causality here. There have been many observations that warmer temperatures correlate with reduced cloud cover. The mainstream models basically assume that temperatures cause cloud cover changes, and I think Spencer is correct to say that this assumption has not been properly verified.
I say this as someone whose academic and professional specialty for the last 30 years has been feedback control systems. As such I am astounded that there has been virtually no attention paid in mainstream climate science as to the direction of causality in this relationship.
That said, I don’t see anything here that demonstrates in any conclusive sense that the direction of causality goes that other way — that is, we don’t yet have the information to say that cloud cover changes (of whatever origin) cause temperature changes.
“Cumulonimbus has been on the increase while Nimbostratus has been on the decrease. I’ll add that figure. Like I said disentangling it all will be a challenge. – Anthony”
This is perfectly consistent with the basics from Leroux. His seminal work from 1993 explains why.
http://ddata.over-blog.com/xxxyyy/2/32/25/79/Leroux-Global-and-Planetary-Change-1993.pdf
His final book was published in 2010. Dynamic Analysis of Weather and Climate, Springer/Praxis, 2nd English Edition.
I find it curiously hilarious that Google ads decided to display an ad for Cloud Computing. That particular cloud has definitely been on the increase. Hahaha.
With all this science going on you’d think it would be warmer than it is, but I still have spring moss in my grass and summer is winding down in the PNWet. Cooler is the missing news everywhere I look. Sure we had some warm days, but the cooler times have been more frequent. The arctic is warming meaning it is losing heat to space at the greatest rate in recent times, and all the indicators are we are, as a planet, shedding heat to the uncaring blackness of space at unprecedented rates. That heat is coming from the lower latitudes. This can’t be good in the long term. Will there be enough CO2 next year for my sweet corn and red potatoes? Should I plant my watermelons or roast the seeds? Do I put in winter wheat in the spring? Where is the heat going?
Leif: “Except that as solar activity has generally decreased [hence cosmic ray intensity increased], Svensmark’s hypothesis would predict an increase in cloud cover. So, no need to look there.”
Tropical cloud cover seems to be increasing and also seems to (inverse) correlate quite well with cosmic ray intensity.
REPLY: Right, and much of the tropical cloud cover is Cumulonimbus. While there may be a correlation, I don’t know that cosmic rays help in tropical Cb formation more than say, increased aerosols. There are many factors to disentangle. – Anthony
Great
Perhaps the author will send some of this ‘less cloudiness’ to the UK for the rest of our ‘summer’. That will make up for the poor overall weather we’ve had so far.
Also note the changes in low level clouds versus middle and high level clouds is an order of magnitude greater than the change in total clouds. The former decreasing and the latter increasing.
This for me is persuasive that the changes are due to reduced anthropogenic/biomass burning aerosols.
http://climate4you.com/images/CloudCoverAllLevel%20AndWaterColumnSince1983.gif
The size of the change in South America is interesting. The Amazon basin has the largest forest fires in the world.
Studies show a declining trend in biomass burning in S America.
http://www.atmos-chem-phys.net/12/7543/2012/acp-12-7543-2012.html
Interesting, though, the high altitude clouds being in decline and low altitude increasing, that would mean cooling actually, or at least compensating the overall effect of cloud reduction. Also, it would represent a positive feedback. This will be interesting to follow.
The climate4you site shows the same thing with the satellite obs of cloud cover. Approximately a 4% decrease centred around the mid 90s prior to the jump in global temps.
Everyone has missed the obvious boom and bust in stratospheric water vapour caused by the mt Pinatubo eruption that continues to this day (effectively multidecadal volcanic warming) . SO2 from eruptions combines with H2O before being rained out leaving the stratosphere H2O diminished. This results in stratospheric Cooling and probably alters the meridional/zonal patterns in weather via the polar vortexes.
I also suspect that if Solar has a climate effect it would be through a similar mechanism with the UV/ozone system.
A also wonder if solar climate changes are related to the change in solar energy rather than the level. Increase in activity (unstable spring weather in stratosphere) =cooling. Decreases in activity (stable fall weather) =warming. This would help explain such paradoxes as the large solar cycle in the 70s corresponding with a period of global cooling.
In another thread Leif produced evidence for the changes in cloud quantities at different levels which appeared to show that high and medium clouds decreased until around 2000 but have been increasing since.
Perhaps he should reproduce it here again.
In the meantime the Earthshine project suggests declining global cloudiness and albedo until around 2000 and a recovery since:
http://wattsupwiththat.com/2007/10/17/earths-albedo-tells-a-interesting-story/
The most likely reason for changing cloud amounts globally is not the Svensmark hypothesis but the changing jetstream behaviour towards increasing zonality with less clouds up to about 2000 then increasing meridionalityafter 2000 with more clouds.
Svensmark deals with lower level cloud as explained in the documentary “The Cloud Mystery” which I strongly urge everyone to watch:
[ http://www.youtube.com/watch?v=ANMTPF1blpQ ]
I note that this paper refers to cloudiness overland only but that is only 30% of the Earth’s surface and heavily influenced by topography.
The topographical influences may well be obscuring the detail of the global trends.
Interesting paper by Eastman and Warren. They do make the observation:
“This global decrease in cloud cover alone could account for all surface warming observed since the 1970′s.”
A sustained decrease in global cloud cover MUST cause an increase in surface warming. Dr Spencer apparently calculates that a 1-2% decrease would result in a warming trend of about 0.8°C/century. If there have been other contributing factors in the past 40 years, they must have balanced out.
That begs the question whether this cloud decrease could have been driven (in some mysterious way) by greenhouse gases. If not, the IPCC will need to re-write its drafts for next year’s assessment report.
Interesting that the largest increase in sunshine has occurred in Oceania.
I know Pinker stated their Pinker et al 2005 paper (cited in AR4) should not be construed as meaning less clouds were allowing more sunlight to reach the earth, but isn’t this paper effectively saying something similar?
“ Clouds, which cover about 60% of the Earth’s surface, are responsible for up to two thirds of the planetary albedo, which is about 30%. An albedo decrease of only 1%, bringing the Earth’s albedo from 30% to 29%, would cause an increase in the black-body radiative equilibrium temperature of about 1°C, a highly significant value, roughly equivalent to the direct radiative effect of a doubling of the atmospheric CO2 concentration.”
from the IPCC report AR4 1.5.2 p.114
http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter1.pdf
What was that about cloud- producing ships, again?
If temperature rises, relative humidity drops and you get less clouds. So what comes first, higher temperatures or less clouds?
Judging from NASA’s Spaceweather.com sunspot numbers so far this month, we are due for a downtick on their graph of monthly sunspot number progression.
Not that that short-term variation is significant in itself, but I would have thought that Svensmark’s hypothesis could have been easily tested by plotting such short term variations in solar activity against satellite observations of global cloud cover over a similar time period and looking for any correlation.
In fact it’s such an obvious test of his hypothesis that I must have missed reporting either of this having been done or an impediment to such a test.
“… doesn’t one of the foundations of CAGW suggest that as it warms there will be less cloud and thus less rain? No references, just a hazy recollection” – Andrew Girle
No, the expectation was imperceptibly more rain overall, but increased rainfall poleward of 50°N and monsoonal regions. The slight overall increase in rainfall corresponds to the ~0.1% decrease in specific enthalpy of water on evaporation per 1°C of temperature rise.