Guest post by Dr. Pat Michaels – reposted (with permission) from World Climate Report
A new paper just published in Geophysical Research Letters by Roger Davies and Mathew Molloy of the University of Auckland finds that over the past decade the global average effective cloud height has declined and that “If sustained, such a decrease would indicate a significant measure of negative cloud feedback to global warming.”
Davies and Molloy are quick to point out that part of the decline from 2000 to 2010 in cloud height is due to the timing and variability of El Niño/La Niña events over the same period, however, there still seems to be evidence that at least part of the decline may remain even when El Niño/La Niña variability is accounted for.
Figure 1 (below) shows the history of the effective cloud height, as determined by Davies and Molloy from satellite observations, from March 2000 through February 2010.
Figure 1. Deseasonalized anomalies of global effective cloud-top height from the 10-year mean. Solid line: 12-month running mean of 10-day anomalies. Dotted line: linear regression. Gray error bars indicate the sampling error (±8 m) in the annual average (source: Davies and Molloy, 2012).
The dotted line is the linear trend through the data as determined by Davies and Molloy and has a value of -44 meters per decade (+/- 22m). However, clearly the trend is influenced by the large negative departure centered around the beginning of 2008 that was related to a moderate La Niña event in the Pacific Ocean. To avoid the influence of the this event, Davies and Molloy calculate the difference between the cloud heights during the first and last years of their record and still find a decline of 31 m/dec (+/- 11m). Although this latter technique doesn’t fully account for the El Niño/La Niña signal in the record, it does at least give some indication of the influence of the large negative departures in the latter half of the record, and indicates that the overall decline is not simply an artifact of a single event.
The average global cloud height is linked to the average global temperature—generally, the higher the average cloud height, the higher the average surface temperature, and vice versa. The tie-in is related to the height in the atmosphere from which clouds radiate long-wave radiation to space. The higher up they are, the cooler they are, and thus the less radiation they lose to space, which means the surface stays warmer.
Davies and Molloy calculate that on a decadal basis, the radiative forcing from increasing greenhouse gases is the same as that caused by either a decrease in the total global cloud amount of ~0.3% (which would allow more short wave radiation from the sun to hit the earth’s surface) or an increase in the global average cloud height of ~19 meters (about 62 feet). All to say, that clouds play a major role in the earth’s climate and that small changes in cloud characteristics can add to (via positive feedbacks) or offset (via negative feedbacks) the warming pressure put on the climate from increasing greenhouse gases. A point well-recognized by Davies and Molloy when they write “Changes in cloud properties in response to rising surface temperatures represent some of the strongest, yet least understood, feedback processes in the climate system. “
Davies and Molloy hoped to better our understanding of cloud behavior by quantifying changes in cloud heights as determined from data obtained from the Multiangle Imaging SpectroRadiometer (MISR) carried aboard the Terra satellite. The MISR data provides stereo imaging that can be used to determine the heights of clouds. The MISR data is not perfect, as it misses very thin clouds (like high level cirrus) and very homogeneous clouds (like some cirrus from thunderstorm anvils), but perhaps its biggest shortcoming is that the period of available data is still pretty short (i.e., only begins February 2000). Nevertheless, an investigation of what data is available from the MISR instrument can provide some insight as to the variability of cloud heights and their relationship to the earth’s climate.
Which was the main purpose of the work of Davies and Molloy.
In full recognition of the limitations of the data, here is how Davies and Molloy conclude their paper, in their own words:
Finally, we note that the climate data record of [effective cloud height] anomalies may ultimately indicate a measure of long-term cloud feedback that may be quite separate from the correlations discussed above [i.e., correlations with El Niña/La Niña]. Ten years is unfortunately too short a span for any definitive conclusion, as the linear trend in global cloud height of -44 +/- 22 m over the last decade is partly influenced by the La Niña event, and may prove ephemeral. The difference between the first and last year of the decade, not directly affected by the La Niña event, is -31 +/- 11 m. If sustained, such a decrease would indicate a significant measure of negative cloud feedback to global warming, as lower cloud heights reduce the effective altitude of emission of radiation to space with a corresponding cooling effect on equilibrium surface temperature. Given the precision of the MISR measurements, we look forward to the extension of this climate data record with great interest.
According to the calculations of Davies and Molloy, the negative climate forcing from a decrease in the average global cloud amount during the past 10 years has more than offset the positive forcing from an increase in greenhouse gases from human activities. It is little wonder that the rate of global temperature rise during this period has been so paltry!
Davies and Molloy write that they “look forward to the extension of this climate data record with great interest.” We want to be the first to second that sentiment.
Reference:
Davies, R., and M. Molloy, 2012. Global cloud height fluctuations measured by MISR on Terra from 2000 to 2010. Geophysical Research Letters, 39, L03701, doi:10.1029/2011GL050506.
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Could we have a plot of the ‘ENSO Meter’ for the same time period?
Just switching back and forth from the page in the sidebar … not sure how well they correlate, really.
Meanwhile rainfall trends in England are pretty static.
http://notalotofpeopleknowthat.wordpress.com/2012/02/09/rainfall-trends-in-england-and-wales/
“more than offset the positive forcing from an increase in greenhouse gases from human activities. ”
This is, f course, assuming that these GHGs are really doing anything. We know that CO2 is pathetic and ineffective and that the IPCC insists on water vapor being a slave to CO2. As we know that this is not true, then the question is still real that regarding rising CO2 having any effect at all on temperatures. It really is not a GHG, only by the strange definition given it by the IPCC. N2 and O2 trap heat as they have no way to emit IR. CO2 and water vapor can emit IR just fine and thus serve to bleed IR to space, particularly at night. In the land of the IPCC there is no night.
Compare that graph to the sunspot numbers of 2008. Hmmmmm.
Count this paper, Spencer’s Cloudfeedback paper and Svensmark’s Cern experimet 1+1+1= 3
1 + Sun 1 + Controls 1 + Climate = 3 Climate sensitivity to CO2 is 0 it wont warm a thing.
CO2 ice is good for cooling icecream. 🙂
I see no statistically significant trend in Figure 1.
“a decrease in the average global cloud amount during the past 10 years”
Is that a typo ?
Average cloud height has declined or so they say but according to other sources cloud amounts have increased over the past ten years.
The length of daylight in the Northern Hemisphere is increasing. This increase has been going on for at least two months. If sustained, this increase will inevitably lead to 500 hours of daylight and -476 hours of night in each 24-hour period. We need to stop breathing RIGHT NOW!
Polistra
“We need to stop breathing RIGHT NOW!”
That isn’t strictly necessary – we can keep breathing in as long as we don’t breathe out. 😉
Gaia knows best!
Davies and Molloy… point out that part of the decline… is due to the timing and variability of El Niño/La Niña events…, however, there still seems to be evidence that at least part of the decline may remain even when El Niño/La Niña variability is accounted for.
Correlation does not necessarily equal causation; however, this may be additional evidence supporting Svensmark’s theory.
Here’s a new graph showing a significant increase…
http://www.heritage.org/research/reports/2012/02/~/media/Images/Reports/2012/02/cda1202/CDA2012indexdependencegovtchart1.ashx?w=400&h=737&as=1
‘All to say, that clouds play a major role in the earth’s climate and that small changes in cloud characteristics can add to (via positive feedbacks) or offset (via negative feedbacks) the warming pressure put on the climate from increasing greenhouse gases. A point well-recognized by Davies and Molloy when they write “Changes in cloud properties in response to rising surface temperatures represent some of the strongest, yet least understood, feedback processes in the climate system. “’
Yes, yes, yes!!!! The claim that human made CO2 can cause rising temperatures turns crucially on the claim that the effects of rising CO2 cause positive “feedbacks” in phenomena such as cloud behavior. In turn, the latter claim depends on the existence of well confirmed physical hypotheses which can be used to explain and predict cloud responses to rising CO2. As of this date, no mainstream climate scientist has produced such hypotheses. They seem not to be interested.
Davies and Molloy provide data and data analysis that takes us ever closer to such hypotheses. But surprise oh surprise, the “feedback” is negative. The response of cloud behavior lowers temperatures.
This is the kind of work that promoters of either AGW or CAGW need to be doing. Yet these scientists remain closeted within their computer models and seem completely averse to empirical research. I think that all of us should take every occasion to ask them why. With all the government money flowing into climate research, why is there no system for the atmosphere thqat is comparable in its capacities to the ARGO system for the oceans?
I’m glad to see this stuff start to be published more frequently. When I say “this stuff”, I’m referencing mechanisms and phenomena which up until recently were associated with our actual climate.
The sun and clouds, throw in some wind and ocean currents and they might have a good general idea about what comprises our climate……… naaw….. let’s go chasing around some trace gas or two and attach meaning to every cow fart we detect.
What is quite extraordinary is how much is NOT known about the physics of clouds.
Graeme Stephens delivered the Charney Lecture recently at the Fall Meeting of the AGU (American Geophysical Union). Video of that lecture is available at
http://sites.agu.org/fallmeeting/scientific-program/lectures/bowie-and-named-lectures/6dec/
I strongly recommend this as it is extremely enlightening as to the specific details of cloud physics which have not been adequately characterised.
I simply cannot agree with this logic about clouds “The higher up they are, the cooler they are, and thus the less radiation they lose to space, which means the surface stays warmer.”
One could say the higher they are the sooner they will reflect incident radiation back to space before it warms some of the atmosphere below it.
Less radiation to space may well mean the atmosphere gets a little warmer, but then we do still have carbon dioxide to help with the radiation to space and thus cool the atmosphere.
But my main point is that there is only one way in which thermal energy from the atmosphere can get back to the surface. It does not “fall” out of the sky by downward convection. It does not get radiated back down because radiation from a cooler source cannot transfer thermal energy to the warmer surface. The only way it can transfer back to the surface is by being transported downwards in precipitation. Yes, cooler clouds mean cooler rain and more hail and snow.
The fact that the clouds are getting lower and warmer may well be a reason why the world is perhaps not cooling quite as much as the 60 year cycle would appear to cause. But then, there is still a slight rise in the ~1,000 year cycle of about half a degree C per century and that may still have one or two centuries before reaching its maximum.
And, by the way, there is absolutely no “positive forcing from an increase in greenhouse gases from human activities.” The author needs to catch up with the fact that, as Prof Claes Johnson has proved in Computational Blackbody Radiation, (summarised on my site) radiation from the atmosphere has a frequency which is below the cut-off frequency for absorption by the surface, so it is merely reflected or scattered without slowing the rate of cooling or increasing the rate of warming of the surface one iota.
Surely its intuitive isn’t it that Global Warming will alter cloud height..
Imagine a (liquid) water molecule at the surface. It takes a huge amount of energy (~2200Joules per gram) to turn it into a vapour. Once airborne, it has nowhere else to go but up, pushed by convection and also diffusion and its own partial pressure amongst the other atmospheric gasses.
Being very sticky stuff as it is (hence the huge Latent Heat of evaporation) it will want to condense, to join back together with all its other airborne siblings. But, if there is a significant energy flux at whatever height it chooses to do its condensing, that flux will prevent condensation. Therefore it will keep on rising until it finds a place/altitude where it can get peace and quiet and actually condense. By definition, it will then be out of the way of any energy flux, especially coming from other GHGs and all the photons of Latent Heat it emits as it condenses get a ‘free run’, upwards and outwards. Water is constantly punching holes through the insulating envelope of GHGs and will go to whatever lengths (altitudes) necessary to lose its Latent Heat.
Hence, less energy, less greenhouse effect means lower clouds. Simples.
Trenberth’s missing heat has all gone, its way out past Alpha Centauri and a good way towards Betelgeuse by now and is moving at 3 times 10 to the eight metres per second. Not even Al Gore can bring it back now.
Doug Cotton wrote:
>>But my main point is that there is only one way in which thermal energy from the atmosphere can get back to the surface. It does not “fall” out of the sky by downward convection.
The primary heat transport mechanism between clouds and the Earth’s surface in convection, evaporation and condensation. Radiative transfer is very small because of relatively small temperature differences (30 degrees C or so). This applies to the 70% of the Earth’s surface covered by clouds.
The sky is falling!
It’s worse than we thought!
Climate Review: III
by Bob Carter
February 9, 2012
Being the final part of a summary and analysis of selected events and papers relevant to global warming, in Australian political context. Climate Review: I is here and Climate Review II is here.
http://www.quadrant.org.au/blogs/doomed-planet/2012/02/climate-review-iii
This is, f course, assuming that these GHGs are really doing anything. We know that CO2 is pathetic and ineffective and that the IPCC insists on water vapor being a slave to CO2. As we know that this is not true, then the question is still real that regarding rising CO2 having any effect at all on temperatures. It really is not a GHG, only by the strange definition given it by the IPCC. N2 and O2 trap heat as they have no way to emit IR. CO2 and water vapor can emit IR just fine and thus serve to bleed IR to space, particularly at night. In the land of the IPCC there is no night.
Truly, this merely indicates that you don’t understand how the GHE works, or the importance of the work in this paper. As the paper states, the major factor in the GHE is the temperature at which atmospheric heat is lost. It has nothing to do with “trapping heat” — it has to do with how rapidly they lose heat. O2 and N2 lose heat by transferring it to the CO_2 and H_2O which can then radiate the heat away, the only way any part of the upper atmosphere can lose heat. If the CO_2 is cold when it radiates the heat away, it dissipates the heat slowly and overall temperatures underneath rise. If it is warmer, it loses it more rapidly and overall temperatures fall. Ditto water and radiation from the cloud tops.
The point of the paper is that lower cloud tops mean warmer clouds doing the radiation, hence faster cooling, hence lower temperatures. However, the evidence for this is not yet compelling, even to the authors. It is merely suggestive and plausible. The hypothesis would be strengthened if the trends and response to the trend continues, or it might be strengthened with a more precise, less heuristic assessment of the feedback. The authors do not address, for example, what the effect of water vapor above the cloud tops might do to the outgoing radiation from the cloud tops. One possibility is re-absorb it and emit it again from higher and colder, negating the effect. The other thing the authors do not address is the confounding observation that stratospheric H_2O has dropped by some 10% over the last decade plus, significantly opening a hole there that in principle also permits more radiation from water vapor to escape from higher temperature, lower collections of water vapor. They aren’t really to blame for this — it is a very complicated system and everybody is doing all they can to look at a linearized (possible) effect from changes in just one small part of it.
In the end, the best conclusion is indeed that it suggests that there is more negative feedback in the system than previously believed, but it isn’t clear why cloud tops are dropping now but might have been rising before when CO_2 levels and temperatures were still rising. It’s unlikely that the cloud top movements are the proximate cause, in other words — they are more likely themselves an effect.
rgb
I would hate to have to tease out the AMO and ENSO effects along with the effects of lower solar activity.
10 years is not enough time to indicate anything at all.
Global temperatures are falling with a big dip in 2008, cloud height is decreasing with a big dip in 2008. What is the mystery? Why are they talking about global warming?
Robert Brown says:
February 9, 2012 at 3:18 pm
The other thing the authors do not address is the confounding observation that stratospheric H_2O has dropped by some 10% over the last decade plus, significantly opening a hole there that in principle also permits more radiation from water vapor to escape from higher temperature, lower collections of water vapor.
==================================================
That would be confounding. Do you have a link for the reference? I’d be most interested in seeing that. If this can be stated with reasonable confidence, then we have a huge problem. Because sea-level rise hasn’t just slowed, it has been reversing itself. In spite of the Himalayas remaining the same, we’re told that much melt is occurring on Greenland and Antarctic is supposedly shedding ice.