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.
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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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Could there be a correlation between the amount and type of air travel and aircraft movements and the formation and height of clouds.As more efficient aircraft come into service and the GFC and internet slows the number of flights, could fewer ionised particles formed in jet exhausts reduce the seeding of clouds?
Can anyone give me a clear quotation from the original Eastman & Warren 2012 (EW2012) paper where it is stated that changes in cloudcover has caused global warming? It looks like the authors conclude the opposite: It is climate change which causes cloudcover and cloud properties to change/evolve and not what is being speculated here. So in fact what EW2012 are saying is that cloudcover changes are a feedback of climate warming.
Dr. Spencer is claiming the opposite of what Eastman & Warren are saying.
Who is right and who is wrong is the big question?
– “Cloud cover will continue to evolve in a changing climate while surface reports of visual
observations may continue to decline in number.”
– “Climate observations and models suggest that cloud properties have changed and will continue
to change in a warming climate. Changes are likely to be seen in cloud amount, height, thickness,
geographical distribution, and morphology. Widening tropical belts and warming polar regions may be
causing a poleward displacement of Earth’s jet streams (Bengtsson et al., 2006; Yin, 2005) and cloudcover
distributions are likely to change with a shift in the location of the mean storm track.”
from http://www.atmos.washington.edu/~rmeast/Full_Text_D1.pdf
Conclusion: The title of this blog does not live up to the content of the paper. The paper is no confirmation of Spencer’s cloud hypothesis at all. For that you need to present the correlation between temperature and cloudcover and also proof what changed first Temperature or Cloudcover. According to EW2012 it was increase in temperature that changed cloud properties and not the other way around.
This finding jibes well with the work on sunshine hours and the strong correlation between them and temperature change.
Less cloud – more-sun – warmer surface – no brainer
http://tallbloke.wordpress.com/2012/02/13/doug-proctor-climate-change-is-caused-by-clouds-and-sunshine/
“The higher the heat the more evaporation and cloud especially Cb cloud, due to the energetic cells, forming especially in the tropics.”
That is correct but global cloudiness (and albedo) does not seem to be strongly linked to Cb cloud amounts in the tropics.
To find the reason for global changes we need to look at a global influence.
One possibility would be global temperature (such as from more CO2) but there seems to be doubt as to whether a higher global temperature gives more clouds (more evaporation and condensation) or less clouds (the air able to carry more water in vapour form). Furthermore our contribution was too small to account for pre 1945 climate changes ( the IPCC concedes that) and there were many of those of a comparable scale to those of the late 20th century.
Another would be internal ocean cycling but that seems to be relatively short term and would not give the long rise in temperature from LIA to date nor the long fall in temperatures from MWP to LIA.
Yet another (the most likely in my view) would be the matter of solar effects acting via the polar vortices from the top down so as to change jetstream positioning and / or the degree of jetstream meridionality as compared to zonality.That would change global cloudiness and albedo without any need to invoke Svensmark’s ideas.
To make a decision we need to sort out cause and effect.
In the late 20th century did the temperature rise first to widen the tropical air masses, push the jets poleward and thereby reduce cloudiness or did the polar vortices change first to reduce the size of the polar air masses and allow the jets to shift poleward ?
To get the temperature to rise first is a problem if the rise in temperature requires more solar input to the oceans to cause that temperature rise. That extra input to the oceans cannot occur unless the clouds reduce first.
So I think it has to be the solar top down effect that caused the reduced cloudiness and then the change in energy input to the oceans increased to cause warming.
The test is whether, as I think to be the case, the reverse process has been in train since around 2000.
Evidence is accumulating to that effect.
In the UK, Met Office graphs show a similarity in patterns between temperature and sunshine hours.
http://notalotofpeopleknowthat.wordpress.com/2012/07/19/uk-temperature-trends/
Ian W says:
August 21, 2012 at 3:32 am
There may be other effects such as cloud seeding by neutrons, but if the amount of water in the atmosphere available to form cloud is reduced that effect will be reduced.
Top graph of http://climate4you.com/images/CloudCoverAllLevel%20AndWaterColumnSince1983.gif
shows that Water content has been dropping too.
It looks like the whole climate picture is still to cloudy to draw any conclusions.
But seriously, I can only offer a simple observation from a golfer. There is always a general concern here in Florida at this time of year that the afternoon will bring thunderstorms due to daytime heating. Not good to out on the golf course then. However, I have noticed that when there are cirrus clouds visible in the AM, the PM thunderstorms are less likely to develop, so we plan out golf accordingly.
This has to tie in somehow with Bob Tisdale’s compelling demonstration of ENSO’s role in most or all of the warming over the last half century. So my bet would be on an ENSO link. A key operative parameter must be the ITCZ (inter tropical converence zone) i.e. the width of the conspicuous band of cloud around the earth’s equator – Stephen Wilde any comments on this?
South America looks the worst to me. That’s what chopping down rain forests does for you.
Leif Svalgaard says:
August 21, 2012 at 3:39 am
IIRC, Svensmark has always been clear that he is talking about lowlevel maritime stratus forming in air cleared of condensation nuclei by rain upstream. E.g. the eastern Pacific. Cosmic rays and dimethyl sulfide gas from decaying algae combine, many steps later, to create nuclei in supersaturated air. The regions of the planet affected are neither large nor well defined on that graph.
I haven’t weighed through the paper yet, but the title includes “from Land Stations” so this may not be a relevant paper.
Re Leif
“Svensmark has always been clear that he was talking about low-level clouds and those have decreased”
Svensmark has always been clear that he was talking about low-level clouds OVER THE OCEANS and this study says absolutely nothing about that.
Thanks for engaging though, you´re one of the few warmists I still find it worth listening to 😉
Reduced clouds due to reduced aerosol-nuclei, which consequently reduce the building of droplets in the atmosphere and, hence, reduce the global cloud-cover overall?
IMHO, It would be interesting to superimpose the availlability of droplet-inducing nuclei and the development of cloud-cover and see, if there’s perhaps a causation involved.
Lewis P Buckingham says:
August 21, 2012 at 3:59 am
Could there be a correlation between the amount and type of air travel and aircraft movements and the formation and height of clouds.As more efficient aircraft come into service and the GFC and internet slows the number of flights, could fewer ionised particles formed in jet exhausts reduce the seeding of clouds?
——————————————————————————————————-
Good point.
It is obvious that CO2 is causing a decrease in cloud cover….
Cedarhill said — Harken back to the days of the Indy 500 and the turbine engines of Andy Granatelli in ’67 and ’68. James Garner (the actor who drove the things) told Johnny Carson they had very slow response time and were just plain dangerous. A 1, 2 or 3+ second delay from when you changed the throttle to when you the car responded.
Sorry Cedar, but in the interest of history, we must note that it was Parnelli Jones who drove the turbine cars…and came within 10 miles of winning before they were banned forever.
Leif Svalgaard says:
August 21, 2012 at 4:34 am
Ian W says:
August 21, 2012 at 3:32 am
There may be other effects such as cloud seeding by neutrons, but if the amount of water in the atmosphere available to form cloud is reduced that effect will be reduced.
Top graph of http://climate4you.com/images/CloudCoverAllLevel%20AndWaterColumnSince1983.gif
shows that Water content has been dropping too.
Thanks Leif, that was my point. You can have as many cloud condensation nucleii as you want – but if there is insufficient water vapor for the air to be saturated or supersaturated then they will have minimal effect.
I think that we need to avoid falling into the ‘global average’ traps too. The amount of water vapor in the air varies considerably. Look at http://www.ssd.noaa.gov/goes/east/natl/flash-wv.html and see the swirls of dry air and (at the moment) the convective storms along the ITCZ. If the dry air with little cloud is held by blocking of the Rossby waves and is over ocean, the ocean will warm and vice versa it may cool.
(for those interested also go to http://www.ssd.noaa.gov/goes/east/natl/flash-rb.html and see the amount of infrared being released by the latent heat as the convective storms on the ITCZ lift water high into the atmosphere and it condenses then freezes.)
You’re forgetting one important step: Condensation (the formation of ‘suspended’ liquid water about a seed particle of some sort which then comprises the ‘cloud’ … don’t forget all the physics involved therein)
.
A few things jump out at me
So this only represents continental area, not ocean area. Furthermore, Antarctica seems to be excluded. Since data for 3/4 of the world is missing, it is very difficult to extrapolate this ~1.6% change over land to predict the global change.
Interesting. As Rob JM and others have pointed out, there is much data on Climate4you that bears this out. I mull over the climate4you data here: http://greenerblog.blogspot.co.uk/2011/09/cloud-cover-decreases-in-warming-planet.html.
It is clear from the data that cloud cover is inversely proportional to global temperature.
The essence of the problem lies in the direction of causality. Do increased clouds cause global cooling, or does global warming cause less cloud cover? Or is it a bit of both?
I could find no perceptible lag between the cloud and temperature traces that would give a clue as to causality.
Simple physics teaches us that less cloud is to be expected in a warmer atmosphere.
The data on climate4you also shows that high altitude cloud, which has a warming effect, increases in a warming atmosphere, and that the low altitude cloud, which has a cooling effect, decreases in a warming atmosphere.
This suggests that the net effect on cloud in a warming world will be to have a positive feedback effect, (which is in keeping with Dessler’s findings) but that this effect, fortunately, will diminish with progressive warming.
“Warmer atmosphere” – or warmer conditions as measured at the surface of a sphere at the center of the atmosphere (which is assumed to be ~ 70% liquid covered)?
.
phlogiston asked:
“A key operative parameter must be the ITCZ (inter tropical converence zone) i.e. the width of the conspicuous band of cloud around the earth’s equator – Stephen Wilde any comments on this?”
Yes. The ITCZ is a key operative parameter as per Willis Eschenbach’s Thermostat Hypothesis.
But it needs to be extended globally.
When the tropical air masses expand at a time of active sun due to the polar air masses shrinking the extra solar energy into the oceans energises the ITCZ but the extra upward flow has to come down again which helps to enlarge and extend the subtropical high pressure cells as they expand poleward to take advantage of the contraction of the polar air masses.
As regards ENSO the additional energy into the oceans also increases the power of El Nino events as compared to La Nina events which gives upward temperature stepping from one positive PDO phase to the next as per Bob Tisdale’s findings.
We would see upward stepping every 60 years or so whilst the sun is getting more active such as from LIA to date and downward stepping every 60 years or so from MWP to LIA.
“The data on climate4you also shows that high altitude cloud, which has a warming effect, increases in a warming atmosphere, and that the low altitude cloud, which has a cooling effect, decreases in a warming atmosphere”
Is that the right way round ?
http://climate4you.com/images/CloudCoverAllLevel%20AndWaterColumnSince1983.gif
Leif, do you wish to retract your claim that a paper regarding cloudiness over land can be used to critique Svensmark?
“The essence of the problem lies in the direction of causality. Do increased clouds cause global cooling, or does global warming cause less cloud cover? Or is it a bit of both”
If one ignores CO2 as a signifcant influence one has to find a means of warming the system before the clouds reduce if warming is to be the cause.We can ignore CO2 for the moment because this has all happened before and we want to know the natural mechanism before we put CO2 in its place.
TSI changes are insufficient so ignore that too.
Warming has to be caused by more solar energy getting into the oceans so the clouds must reduce first.
The sun must cause a change in the global air circulation that reduces clouds when the sun is more active.
Hence latitudinally shifting jets with increased zonality and wider tropical air masses at a time of active sun.
If anyone has another way of warming the system without the clouds reducing first then let’s hear it.
“It is obvious that CO2 is causing a decrease in cloud cover….”
Possibly that was sarcasm but I’ll treat it seriously.
CO2 is still increasing but since around 2000 there has been an increase in high and medium clouds and total global albedo.