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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Thank you for the link to Richard St. Barbe Baker’s re-forestation efforts.
Clearly, he was a great conservationist.
My reflection on trees has two components. [ Again, I am NOT a climatologist]
1. The CO2 graph has appeared to me to be a linear function.
2. De-forestation and agricultural growth along with population growth over the past 150 years are the best matches I’ve seen with the CO2 graph.
However the loss of trees, at massive scale isn’t just the recent Palm Oil / Rain Forest situation.
The start of trade following the 1880 “Gilded Era” gave us:
1 Gypsy Moth – Imported for to strengthen silkworms. Some escaped. Now, vast stretches of forest defoliate from Maine to Virginia and West to Ohio.
2. Dutch elm disease – Came in two waves. It was the second in the late 1920s where the virus was lethal. This strain also bounced back to Europe. The numbers are staggering. 25 million in the U.K., 80 to 100 million in the U.S. and still spreading. Canada is next.
3. The worst is the pine beetle. The following New York Times article focuses on the Western USA and Canada. However, these bad guys have moved South as well.
The net rule of thumb is: 50 acres of trees cleans 1 SUV/yr. The cloud formation potential is a possible second benefit.
http://www.nytimes.com/2008/11/18/science/18trees.html?_r=1&pagewanted=all
Well Gail, and others who question that less cloud is to be expected in a warmer atmosphere, Please click on this link : http://climate4you.com/ . This is a not a warmist site, it is a sceptic site.
Click on “Climate and Clouds”, then on “Cloud clover effects on climate”.
There you will find, under a diagram of the effects of clouds (High warming, low cooling, sorry) which graphically displays the observation that cloud cover is inversely proportional to global surface air temperature. As temperature goes up, so cloud cover goes down.
A cooler earth has more cloud.
A warmer atmosphere has less cloud.
Observation based.
Which in fact is nothing but confirmation of what Anthony says right at the top of this page
“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:”
That is, cloud cover has decreased as the planet has warmed over the past 40 years.
So whatever theoretical explanations anyone may advance to the contrary, the fact remains that cloud cover decreases as the planet warms. As we should expect, since water vapour tends to condense into clouds less easily in warm air.
I hope this is helpful.
Robert Doyle says:
August 22, 2012 at 11:34 am
You are assuming cause in the cloud – surface temperature relationship.
Assume a static climate and then reduce the level of aerosols. This decreases cloud persistence and generally cloud reflectivity. Surface temperatures rise.
If as you claim, increase surface temperatures cause decreased clouds, Decreased aerosols, as has happened across much of the world over the last 40 years, would cause a positive feedback loop and runaway warming. This hasn’t happened. Therefore, increased surface temperatures do not cause decreased clouds.
“””””…..docrichard says:
August 22, 2012 at 3:47 pm
Well Gail, and others who question that less cloud is to be expected in a warmer atmosphere, Please click on this link : http://climate4you.com/ . This is a not a warmist site, it is a sceptic site.
Click on “Climate and Clouds”, then on “Cloud clover effects on climate”.
There you will find, under a diagram of the effects of clouds (High warming, low cooling, sorry) which graphically displays the observation that cloud cover is inversely proportional to global surface air temperature. As temperature goes up, so cloud cover goes down……”””””
Well doc, I much prefer actual real world experimental observation and measurement to blog pots, rgeardless of the point of view (bias if yoy will) of the blogger.
So if you check out the peer reviewed scientific paper I cited, wherein Frank Wentz et al of RSS, a somewhat well known weather/climate data sensing outfit; actually measured total global evaporation rates, total global atmospheric water content, and total global precipitation, as a function of mean global surface Temperature, and then they compared their actual observed real results to those seat of the pants machinations of the terraflop computer so called GCMs. The results are in their SCIENCE paper “How much more rain will global warming bring ? ” July-7 2007
Briefly they found the INCREASE rate for a one deg C mean global Temperature increase, was 7% for ALL THREE of those variables.
Not surprising that total global precipitation always equals total global evaporation; tends to keep the oceans from being overhead.
The GCMs also agreed on those two rates. Not so surprising, since the evap is little more than the Clausius Clapeyron equation in action.
But the super models claimed only a 1-3% increase in total atmospheric water content, globally. That is an error of as much as a factor of seven from actual real physical experimental observations and measurements.
Now, I don’t recall Wentz et al, actually mentioning the amount, density or persistence of cloud cover; nor the locations where clouds tended to form.
If a one degree rise in global mean Temperature observationally results in a 7% increase in total global precipitation; just take a wild arse hip shoot guess as to what might be the amount of INCREASE in total global PRECIPITABLE CLOUD COVER / AREA / DENSITY / PERSISTENCE TIME ??
I don’t know about your local climate / weather, but everywhere I have ever been, it has been customary to have precipitable clouds associated with precipitation. I would tend to put my money on about a 7% increase in precipitable cloud cover; but that is not any peer reviewed observation; or even a terracomputerflop computation; really just a WAG !
@george E. Smith:
Or they can just watch the “movies” here:
http://earthobservatory.nasa.gov/GlobalMaps/
“net radiation”
http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=CERES_NETFLUX_M
sea surface temperature:
http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MYD28M
Water vapor:
http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MYDAL2_M_SKY_WV
Clouds:
http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=MODAL2_M_CLD_FR
Precipitation:
http://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=TRMM_3B43M
As the year progresses, you can see that they “all go together when they go” smoothly moving up and down the globe. More sun, surface temp, more water vaporizing, more clouds, more precipitation, more …
docrichard
High and medium clouds decreased whilst the globe was warming and are now increasing as the globe cools.
Low clouds increased with warming and are now decreasing with cooling.
What we see is a shift in the balance between insulation from low clouds and reflection by high clouds.
For temperature to be causing the cloud changes you somehow have to change temperature first without any change in solar input to the oceans. It is proposed that CO2 was the cause but that has been falsified by the changes in trend of both cloudiness and temperature since the late 90s whilst CO2 continues to rise.
Thus the change in cloudiness has to come first in order to allow more energy into the oceans and warm up the globe.
A decrease in high and medium reduces reflection to allow more energy in and an increase in low clouds at the same time holds the energy in the oceans longer via increased insulation. Thus warming as per the late 20th century.
We now have an increase in high and medium for more reflection and a decrease in low for less insulation. A cooling setup which is now affecting ocean heat content but has yet to fully impact on the troposphere.
If one were able to increase temperature first, with cloudiness following, then that extra warmth would produce more clouds and precipitation and not less clouds and precipitation.
AGW theory proposes that increased warmth from more CO2 produces more water vapour from increased evaporation but then proposes that somehow the extra water vapour fails to condense to form clouds and precipitation.
We can discount that because global humidity shows either no change or a change in the wrong direction and anyway the link is already falsified as I pointed out above.
In practice what happens is that the sun changes the circulation to reduce high and medium clouds but low clouds increase somewhat leaving humidity much the same. Cloud totals fall because high and medium clouds are deeper than low clouds and so have a greater effect on total cloud quantities if they change volume.
Warming then occurs which energises the convective processes in the tropics and in due course also the mid latitude depressions. As energy is pushed poleward faster.In the process clouds and precipitation do increase but that is not the primary driver. That is simply the negative system response responding to the original solar effect from above which was to cause a global cloud reduction.The faster processes are offsetting the increase in energy to the oceans by increasing the rate of loss to space.
The whole thing reverses when the sun changes the circulation in the other direction.
Then, the solar effect is to increase high and medium but reduce low. Cooling then occurs which reduces the convective processes in the tropics and the mid latitude depressions are able to wander about more freely but again that is not the primary driver. That is simply the negative system response to the original solar effect which was to cause a global cloud increase.The slower processes are trying to offset the decrease in energy to the oceans by reducing the rate of loss to space.
The secret behind all this is that whatever happens to the energy budget the air circulation will always respond in a negative fashion so as to maintain system energy by matching longwave radiation out to solar radiation coming in.
In the process of achieving that balance the atmospheric heights change, the gradient of tropopause height between equator and poles changes and the climate zones and jets shift about latitudinally with changes in the amount of cloudiness being caused by the changes in jetstream behaviour between zonality and meridionality.
An active sun causes less clouds by causing more zonality and a quiet sun causes more clouds by increasing meridionality.
The sun achieves that effect by altering ozone chemistry differentially between equator and poles so that the tropopause height gradient changes between equator and poles.
The reason that the thermal energy balance must be maintained is related to atmospheric pressure but that is another story.
Henry says
http://wattsupwiththat.com/2012/08/20/spencers-cloud-hypothesis-confirmed/#comment-1062747
Henry@Stephen Fisher Wilde
In light of your previous post, don’t you think the E and F can go together? Well, at least it seems logical to me that from F changes in clouds also follow. That means one could link changes in sun cycle activity to cloud streams and- formation as well.
From HenryP’s earlier post:
E. Sun cycle activity related to the movement of the major (tropic) cloudbanks either more towards the equator or more towards the poles
F. sun cycle activity related to a small variation in UV light from the sun, which affects the amount of ozone production in the stratosphere (a certain type UV light converts oxygen into ozone); ozone re-radiates a lot of high energy sunlight to outer space and if there is less of it allows more energy in.
Yes, they go together but I’m not sure that re-radiation by ozone is a major factor. More likely there is a change in the quantities of ozone available to warm up in response to incoming solar irradiation. It is the amount of ozone present that creates the temperature inversion in the stratosphere when it warms up from solar irradiation.The more there is the stronger the inversion.
Anyway, that isn’t critical. For whatever reason the changes in solar activity alter stratospheric temperatures over the poles differently to the change over the equator so that the slope of the tropopause height changes between equator and poles.
You have to change the temperature of the stratosphere relative to that of the troposphere in order to change tropopause height and it would be unlikely that any solar effect would be proportionately identical at both equator and poles due to the uneven distribution of incoming energy onto a sphere with a magnetic field giving priority to some of the incoming at the poles and the atmosphere being higher above the equator.
Differing stratospheric thermal effects at equator and poles alter the tropopause height gradient to allow latitudinal climate zone and jetstream shifting.
There are two consequences but ultimately they are self cancelling thus:
i) More poleward jets with less clouds allows both more energy in AND more energy out.
ii) More equatorward jets with more clouds allows both less energy in AND less energy out.
In the process there are all sorts of regional changes in the air circulation which we call climate change but the system energy content changes very little.
Stephen Wilde says
I’m not sure that re-radiation by ozone is a major factor
Henry@Stephen Fisher
There is a basic misunderstanding there. But I have noticed that you are not the only one who does not see what the ozone is really doing.
This rough graph / representation (on a cloudless day) is very important:
http://albums.24.com/DisplayImage.aspx?id=cb274da9-f8a1-44cf-bb0e-4ae906f3fd9d&t=o
Now look in the oxygen – ozone spectrum on the left hand side and compare it with the incoming solar radiation on the left top. Do you see that the ozone cuts off a lot of incoming solar radiation before 0.3 um? The raleigh scattering also has an effect there, but if you look sideways you will notice that that is really only in a tail. The bulk of the difference i.e the white area between the red line and the actual red area, is due to the ozone re-radiation.
Try to look at that again, and perhaps also here again,
http://www.letterdash.com/HenryP/the-greenhouse-effect-and-the-principle-of-re-radiation-11-Aug-2011
Once you got it, you will realize that a small effect in ozone level, may produce an enormous effect on the incoming high level energy <0.3 um radiation, which is what heats the oceans…, mostly. (Water absorbs in the UV and therefore that radiation must immediately be transformed to heat. There is also some absorption of water in the visible and IR regions, but try heating some water with a beam of such light… it will take a long, long time….).
Another pointer to this reasoning of the fluctuation in ozone being the major factor causing warming and cooling periods is that if the ozone hole (in the SH) gets bigger – as it did in the warm period 1945-1995 – more radiation of <0.3 comes in, through the hole so to speak, without any restriction or barrier whatsoever. That explains my results.
Ted Swart says:
August 21, 2012 at 8:45 am
Come on everyone. Peter Stroud is correct….
_______________________________
As far as I am concerned we are still at the stage where we are trying to list all the factors that might influence the climate and the list is still far from complete.
The sun of course is the origin of ~ all the energy in the system so relegating it to a minor roll seems a bit hasty at least at this time.
When ever you have a system this complex you are going to have confounding factors up the wazoo so the “CO2 is the Control Knob” crap is idiotic.
My bet is sun/water confounded interactions
Ulric Lyons says:
August 21, 2012 at 5:43 pm
Breaking it down, there appears to be no trend in cirrus since 1983:
– Interesting. Cirrus and cirrostratus seem to have decreased markedly in 1992, following cooling produced by Pinatubo volcano in 1991. Cirrus has a bit of an increase after the warm year of 1998. Otherwise as you say there is no trend visible to the naked eye.
docrichard says:
August 21, 2012 at 1:34 pm
Well I’m sorry Ulric, but that’s what we read – from both sides of the divide. If you are interested in it, why not do an in-depth study of the basis for the general statement “High clouds warm, low clouds cool”.
_____________________________
Another piece of evidence is from farming. We pray for LOW CLOUDS to provide insulation when the temperatures might dip to below freezing. Farmers even set up misters to provide more humidity AT GROUND LEVEL.
Stephen, you have a broad set of conjectures, but they need to be tested against data, and presented systematically.
docrichard says:
August 23, 2012 at 7:46 am
“- Interesting. Cirrus and cirrostratus seem to have decreased markedly in 1992, following cooling produced by Pinatubo volcano in 1991. Cirrus has a bit of an increase after the warm year of 1998. Otherwise as you say there is no trend visible to the naked eye.”
And much of the detail follows changes in the solar wind speed:
http://omniweb.gsfc.nasa.gov/tmp/images/ret_1331.gif
http://isccp.giss.nasa.gov/zD2CLOUDTYPES/B101glbp.anomdevs.jpg
Again suggesting a negative feedback.
Ulric Lyons says:
August 23, 2012 at 10:34 am
And much of the detail follows changes in the solar wind speed:
As is obvious from your links, there is no detailed [or even gross] correlation.
HenryP says:
August 23, 2012 at 5:36 am
I don’t have a problem with that because if ozone above the tropopause causes warming and thus a temperature inversion then it can only do it by absorption and reradiation to the surrounding molecules before that energy is lost to space again.
If the energy is being processed at that height then it is being denied to the oceans as you suggest.
Anyway, the details of the relevant processes don’t matter from my point of view and if you have added some useful detail then I appreciate that.
My main question would be as to the scale of the direct ozone reradiation effect as compared to the indirect cloudiness changes affecting albedo.
And it just occurs to me that according to Miscolczi there has been no change in optical depth but it could be that the change caused by the ozone might be offset by something else such as a humidity reduction.
I’m sure we are on the right track but there is a lot of detail to fill in.
“Stephen, you have a broad set of conjectures, but they need to be tested against data, and presented systematically.”
Well they are presented systematically because they pull all the observations into a plausible narrative with causes and effects properly sorted out (in my opinion).
I agree that we do need more of the right sort of data to test it all but such data as has been coming to the fore seems supportive so far.
“””””…..Gail Combs says:
August 23, 2012 at 8:04 am
docrichard says:
August 21, 2012 at 1:34 pm
Well I’m sorry Ulric, but that’s what we read – from both sides of the divide. If you are interested in it, why not do an in-depth study of the basis for the general statement “High clouds warm, low clouds cool”.
_____________________________
Another piece of evidence is from farming. We pray for LOW CLOUDS to provide insulation when the temperatures might dip to below freezing. Farmers even set up misters to provide more humidity AT GROUND LEVEL.
FROST/FREEZE PROTECTION FOR HORTICULTURAL CROPS
….In cloudy, breezy weather, the observed lows are likely to be very close to forecast values, but under clear, calm conditions, frost may need to be anticipated even when no frost is forecast….
All frost/freeze protection methods are based on preventing or replacing radiant heat loss….”””””
Gail, I don’t know about ALL horticultural crops; but I do know something about “fog”/clouds when it comes to grape crops freezing.
And the methodology is quite different, and vastly more powerful, than trying to slpw cooling by LWIR interception. The change in cooling rate by altering fog density is mighty puny at best.
A much more potent physics process is employed. A typical wine grape vineyard that I built (paid to have built) was an 80 acre square parcel, surrounding a square central one acre lake. The lake was filled by a classical windmill, which pumped groundwater whenever wind blew, and could be augmented by a powered well pump for when the wind didn’t blow enough. The 80 acres was fitted with a distributed fine spraying system, linked to the powered pump.
When a freeze was predicted, as the air Temperature got down to zero deg C, the pump came on, and the sprinkler system sprayed a not too fine spray over the vines. This was a spray, and NOT a mist. The water sprayed onto the vines and grapes, and of course started to freeze. The pumps could not keep up with the total spray rate, but they could replenish the lake fast enough so it took about 24 hours to drain the whole lake, which is about twice the longest freeze in these parts.
So long as the spray continues and ice forms, the Temperature of the grapes and vines never goes below zero deg C, and to boot, the cold atmosphere has to remove an enormous 80 calories per gram of water, for it to freeze.. Somewhat more actually because the well water was typically 68 deg F (20 deg C), so it takes 100 alories per gram to freeze that water.
The liquids in the grapes and plant cells are full of sugars and stuff and they are good down to well below zero, so the crps never freeze.
The latent heat of freezing is a superior freeze inhibitor to a puny GHG radiation blockage.
@ur momisugly george e smith
Thanks for the heads-up about Frank Wentz. I could not see his original paper, but he gave an interview about his work here: http://earthsky.org/earth/frank-wentz-will-global-warming-bring-more-rainfall.
He says “I certainly wouldn’t claim that we have any definitive answers. I think, though, we’ve been able to leave behind the upper and lower rates of the expected increase in rain. But to determine what the exact increase is going to be and where the increased rain is going to fall, those are questions that still need to be answered”.
His work confirms that the total water vapour content of the atmosphere will increase in a warming world (mentioning that 99% of the H2O in the atmosphere is as vapour, only 1% as cloud), which confirms the first major positive feedback.
He concludes:
“What’s the most important thing you want people today to know about global warming and rainfall?
Global warming is real. It’s not a hoax. However, one should not expect a perfectly steady increase in temperature. We’ve already seen in the 1990′s that there was a relatively large amount of warming and moistening while this last decade, 2000 – 2010, the warming trends have decreased some. But this type of variability is to be expected and it doesn’t mean that global warming isn’t occurring.
Some decades will warm more and some decades it will warm less. But having said that, I think we also have to acknowledge that the Earth is an extremely complex system to predict and, as I said, particularly with respect to rainfall as opposed to simply predicting overall warming. Our study on how much more rain global warming will bring was intended to put an upper and lower bound on future rainfall intensity increasing. I think most scientists are confident that we will see more rain the future but exactly how much more and where it will occur are still unknowns.”
However, he makes no mention of clouds at all in the interview. I take your point that we should expect more cloud if there is more rain; but if this conversation has taught us anything, it is that cloud science is ridiculously complicated. and despite your stricutres, george, the very clear figure on climate4you is based on observations, and shows unambiguously that cloud cover is inversely proportional to temperature.
How can Wentz be reconciled with these observations? One possibility is through a shift towards CuNims (as shown), where the vapour is condensed, stored vertically and precipitated in a short time, as opposed to stratus clouds, where the opposite happens.
If Wentz is right, the models have been underestimating the amount of water vapour in a warming world, and therefore underestimating (to whatever degree) climate sensitivity and this is the important conclusion.
All in all, this conversation shows the immense complexity of cloud science, its mixture of positive and negative feedbacks. Out of all these complex interactions, there must be some net outcome, and I suspect that Dessler is probably right in concluding that clouds have a weak positive feedback effect.
E.M.Smith says:
August 22, 2012 at 11:29 pm
“As the year progresses, you can see that they “all go together when they go” smoothly moving up and down the globe. More sun, surface temp, more water vaporizing, more clouds, more precipitation, more …”
UK sunshine hours for December and June tell a different story, the range between them is far larger than the number of daylight hours:
http://www.metoffice.gov.uk/climate/uk/averages/8110_1km/Sunshine_Average_1981-2010_12.gif
http://www.metoffice.gov.uk/climate/uk/averages/8110_1km/Sunshine_Average_1981-2010_6.gif
If clouds are present in winter, frost does not form. If it is a clear starry night it forms. Clouds do keep the temps down in summer, but humidity may rise. And from my experience watch the weather become more volatile during the change in seasons.
It might be of interest though a 10 year research project covered the effect on weather and precipitation patterns in South America after expansive tree felling and turning into agricultural land. The level of the clouds rose, and precipitation patterns changed were noticed even 200 kms away. Therefore the natural run off to the Amazon decreased. There is some sense in avoiding expansive block tree clearing. However it was noticed if they left strips of rain forest with smaller areas of grazing land in between, this did not effect the precipitation levels so much or hardly noticeable. I can’t remember the equations but I think it was for every acre cleared they should leave 5 acres uncleared. It then remains self sustaining.
Just a note on clouds and forest which others have mentioned. It is well known that tropical forests, through evapotranspiration, produce their own cloud. There must be a minimum area of forest that can sustain a cloud. I have a recollection that the great Wangari Maathai (founder of the Green Belt Movement that has planted millions of trees in Africa) said that 15 sq km of forest would generate a cloud, but I have been unable to trace the source of this figure.
Whatever the area, reforestation is clearly a good path to follow, not just from the point of view of CO2 sequestration, but also for its effect on the local climate, and its products in terms of food, fodder, medicines, and timber. But it should always be carried out by and for the local community, and be diverse and ecologically sensitive. And it should start at the coast and move inland. http://www.greenhealth.org.uk/DesertRose.htm
Leif Svalgaard says:
August 23, 2012 at 10:43 am
“As is obvious from your links, there is no detailed [or even gross] correlation.”
I disagree, there is much correlation of timing and direction of change, but less with extent, as would be expected due to things like seasonal effects, e.g the majority of the biggest spikes in Cirrus are around mid year.
Ulric Lyons says:
August 24, 2012 at 5:10 am
“As is obvious from your links, there is no detailed [or even gross] correlation.”
I disagree, there is much correlation of timing and direction of change
I guess that is always in the eye of the believing beholder…