Oh dear, now we have three peer reviewed papers (Lindzen and Choi, Spencer and Braswell, and now Richard P. Allan) based on observations that show a net negative feedback for clouds, and a strong one at that. What will Trenberth and Dessler do next? Maybe the editor of Meteorological Applications can be persuaded to commit professional suicide and resign? The key paragraph from the new paper:
…the cloud radiative cooling effect through reflection of short wave radiation is found to dominate over the long wave heating effect, resulting in a net cooling of the climate system of −21 Wm−2.
After all the wailing and gnashing of teeth over the Spencer and Braswell paper in Remote Sensing, and the stunt pulled by its former editor who resigned saying the peer review process failed, another paper was published last week in the journal Meteorological Applications that agrees well with Spencer and Braswell.
This new paper by Richard P. Allan of the University of Reading discovers via a combination of satellite observations and models that the cooling effect of clouds far outweighs the long-wave or “greenhouse” warming effect. While Dessler and Trenberth (among others) claim clouds have an overall positive feedback warming effect upon climate due to the long-wave back-radiation, this new paper shows that clouds have a large net cooling effect by blocking incoming solar radiation and increasing radiative cooling outside the tropics. This is key, because since clouds offer a negative feedback as shown by this paper and Spencer and Braswell plus Lindzen and Choi, it throws a huge monkey wrench in climate model machinery that predict catastrophic levels of positive feedback enhanced global warming due to increased CO2.
The cooling effect is found to be -21 Watts per meter squared, more than 17 times the posited warming effect from a doubling of CO2 concentrations which is calculated to be ~ 1.2 Watts per meter squared. This -21 w/m2 figure from Richard P. Allan is in good agreement with Spencer and Braswell.
[While the -21wm2 and ~1.2 W/m2 values are correct, the comparison is wrong, and it is my mistake. The values are Top of Atmosphere and Surface, which aren’t the same. This prompts a new rule for me, I shall not publish any posts after midnight again (other than something scheduled previously during the day), because clearly I was too tired to recognize this mistake. I’ll add that I have emailed Dr. Allan regarding the question of feedback on hisfigure 7, and have not received a response. – Anthony]
Here’s the paper abstract, links to the full paper (which I located on the author’s website) follow.
Combining satellite data and models to estimate cloud radiative effect at the surface and in the atmosphere
Richard P. Allan
Abstract: Satellite measurements and numerical forecast model reanalysis data are used to compute an updated estimate of the cloud radiative effect on the global multi-annual mean radiative energy budget of the atmosphere and surface. The cloud radiative cooling effect through reflection of short wave radiation dominates over the long wave heating effect, resulting in a net cooling of the climate system of -21 Wm-2. The short wave radiative effect of cloud is primarily manifest as a reduction in the solar radiation absorbed at the surface of -53 Wm-2. Clouds impact long wave radiation by heating the moist tropical atmosphere (up to around 40 Wm-2 for global annual means) while enhancing the radiative cooling of the atmosphere over other regions, in particular higher latitudes and sub-tropical marine stratocumulus regimes. While clouds act to cool the climate system during the daytime, the cloud greenhouse effect heats the climate system at night. The influence of cloud radiative effect on determining cloud feedbacks and changes in the water cycle are discussed.
1. Introduction
Earth’s radiative energy balance (solar radiative energy absorbed and terrestrial radiation emitted to space) determines current patterns of weather and climate, the complexity of which is illuminated by satellite observations of the evolving distribution and diversity of cloud structures. Representing clouds and the physical processes responsible
for their formation and dissipation is vital in numerical weather and climate prediction, yet many approximations must be made in these detailed models of our atmosphere (e.g. Bony et al., 2006; Allan et al., 2007). Observations of cloud characteristics from satellite instruments and in situ or ground-based measurements are crucial for improving understanding of cloud processes and their impact on Earth’s radiative energy balance (Sohn, 1999; Jensen et al., 2008; Su et al., 2010). The energy exchanges associated with cloud formation and precipitation are also a key component of the global water cycle, of importance for climate change (Trenberth, 2011). In this paper, initially presented at a joint meeting of the Royal Meteorological Society and Institute of Physics on Clouds and Earth’s Radiation Balance (Barber, 2011), the utility of combining weather forecast model output with satellite data in estimating the radiative effect of cloud is highlighted. Using a combination of models and satellite data a simple question is addressed: how do clouds influence the radiative energy balance of the atmosphere and the surface.
As an example of the radiative impact of cloud, Figure 1 displays thermal infra-red and visible channel narrow-band images of the European region from the Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) on board the Meteosat-9 satellite (Schmetz et al., 2002).
In both images clouds appear bright: this denotes relatively low infra-red emission to space and relatively high reflection of visible sunlight to space. The hot, generally clear regions of northern Africa are also noticeable in both images since they are associated with substantial thermal emission to space (dark regions in the infra-red image) and high surface reflection from the desert surface (bright in the visible image). The brightest clouds in the thermal image correspond with (1) a trailing cold front extending from the coast of Norway, across Scotland and to the west of Ireland, (2) a developing low pressure system to the west of Iceland, and, (3) a low pressure system in the Mediterranean centred on Sardinia.
These are regions of ascending air with relatively high altitude, low temperature cloud tops which depress the thermal emission to space compared with surrounding regions. These features are also present in the visible image. However, many more cloud structures are also present. There is a prevalence of low altitude cloud over the oceans: this cloud contains large amounts of water droplets which are highly reflective (e.g. Stephens et al., 1978). The imagery captures the complex cellular structure of this cloud (e.g. Jensen et al., 2008) over the region surrounding the Canary Islands. These cloud types are thought to contribute strongly toward uncertainty in climate projections (Bony et al., 2006). While these clouds also strongly attenuate infra-red radiation, their impact on the thermal radiation escaping to space is modest since cloud-top temperatures are not dissimilar to the surface at night and so they do not contribute significantly to the strong natural greenhouse effect of the clear-sky atmosphere.
The altitude and optical thickness of cloud determines the overall radiative impact of cloud, a combination of the warming greenhouse effect and the surface-cooling solar
shading effect. Yet, probably an even stronger influence does not relate to the cloud itself. The time of day and time of year dictate the incident solar radiation and, therefore,
modulates the strength of the short wave reflection: clearly at night the solar influence of cloud is absent.
…
7. Conclusions
Exploiting satellite measurements and combining them with NWP models initialized through assimilation of available observations enables the effect of clouds on the Earth’s radiative energy balance at the surface and within the atmosphere to be quantified for the present day climate. Consistent with previous results (Ramanathan et al., 1989; Su et al., 2010), the cloud radiative cooling effect through reflection of short wave radiation is found
to dominate over the long wave heating effect, resulting in a net cooling of the climate system of −21 Wm−2.
The short wave radiative effect of cloud is primarily manifest as a reduction in the solar radiation absorbed at the surface of −53 Wm−2 for the global multi-annual mean. The magnitude of this effect is strongly modulated by the incoming solar radiation and the dominance of cloud short wave cooling over long wave greenhouse trapping is maximum around local noon (Nowicki and Merchant, 2004) while the cloud long wave heating effect dominates at night.
The long wave greenhouse effect of cloud measured at the top of the atmosphere is manifest primarily as a heating of the atmosphere in the moist tropics, consistent with calculations by Sohn (1999).
Over the marine stratocumulus regions and across higher latitudes the cloud-base emission to the surface becomes substantial and dominates over the reduced outgoing long wave radiation to space resulting in enhanced radiative cooling of the atmosphere and heating of the surface. The cloud radiative influence on the exchange of radiative fluxes between the atmosphere and the surface are intimately linked with the water cycle through radiativeconvective balance. While tropical, high-altitude clouds act to stabilize the atmospheric profile radiatively, clouds over polar regions tend to cool the atmosphere while heating the surface through enhanced atmospheric longwave radiative emission to the surface. In future work it would be informative to categorize these effects by cloud type further (e.g. Futyan et al., 2005) and compare with climate model simulations. These analyses are vital in constraining cloud feedback processes further and in linking to future changes in the water cycle (Stephens, 2005; Bony et al., 2006; John et al., 2009).
A particular challenge is the accurate quantification of surface radiative fluxes due to the sparse ground-based observing network (Roesch et al., 2011) and also monitoring current changes in cloud radiative effect in satellite data, reanalyses and models (Wielicki et al., 2002); combining meteorological reanalyses with satellite data and surface observations provide a vital methodology for meeting these challenges.
Abstract is here: http://onlinelibrary.wiley.com/doi/10.1002/met.285/abstract
Full paper is here: http://www.met.reading.ac.uk/~sgs02rpa/PAPERS/Allan11MA.pdf
UPDATE: Some people in comments including Dr. Roy Spencer, (and as I was writing this, Dr. Richard Allan) suggest that the paper isn’t about feedback (at least in the eyes of IPCC interpretations, but Spencer adds “it could be”). Thus I’ve removed the word from the headline to satisfy such complaints. My view is that clouds are both a feedback and a forcing. Others disagree. That’s an issue that will occupy us all for sometime I’m sure.
Regarding cloud feedbacks, here’s what I noted in the paper in section 6, near the end. Allan is referring to figure 7 which shows (a) net radiation and (b) net cloud radiative forcing:
Substantial negative anomalies in net radiative flux from ERA Interim are apparent in 1998 and 2010, both El Niño years, suggesting that the substantial re-organization of atmospheric and oceanic circulation systems act to remove energy from Earth during these periods.
You can clearly see the famous double peak in the 1998 El Niño, but it is inverted. To me that looks like a thermostat action, and not one with stuck electrical contacts, i.e. a negative feedback. I’ve also updated the text related to the incorrect comparison I made. – Anthony
tallbloke says:
September 20, 2011 at 12:17 pm
John B says:
September 20, 2011 at 12:01 pm
The water vapour and clouds are feedbacks.
So if co2 made it warmer, and that made more water vapour, how come the cloud amount reduced between 1980 and 1998?
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Don’t know, but it looks like more of a problem for Spencer than for mainstream climate science (i.e. there was little or no negative feedback from clouds, plenty of positive feedback from water vapour)
IMHO
John B says:
September 20, 2011 at 12:01 pm
Not so to you too, Sir!
Sorry – but that is the whole illogical basis of the CO2 based AGW theory IMO. It is essentially that a small change in CO2 (a small GHG contributor) causes knock on and supposedly massive changes in other GHG’s water vapour and clouds, etc – but this is simply illogical based on geological past CO2 levels.
I’m relatively happy to accept CO2 is a positive effect, albeit extremely small in terms of the energy kicking around. But the +ve and -ve effects of all the other factors far outweigh any CO2 effect.
In my opinion clouds are the primary regulator/thermostat and THEY are based on water vapour – of which, as a wet planet – we have bucketloads – figuratively speaking! When you consider that H2O is responsible for 80+% of any GH effect (I know the figures vary according to source) – something that contributes peanuts to GHG effect (CO2) is just not on the scale!
Joe Born says… ” Let’s do a thought experiment. Suppose a CO2 increase sufficient to raise temperature 1 degree reduces clouds enough to raise temperature another half degree. That half degree reduces clouds enough to raise temperature another quarter degree . . . so that after an infinite number of such responses the temperature has been raised a total of two degrees.”
For your experiment to be true…. an increase in temperature MUST NOT have much of an effect on cloud cover because the paper in question shows that there is expected to be a huge effect on temperature with only a relatively small change in could cover. Once again, the effect of temperature on clouds is consistent with Dessler and Spencer papers.Therefor one can conclude that factors other than temperature increases that effect cloud cover (cosmic rays, ocean cycles or something else) will have a relatively large effect on temperature. Best evidence indicates a slightly negative feedback between temperature and clouds excluding ALL other factors that influence cloud formation, ie higher temps due to CO2 increase clouds cover slightly which lessens the net warming due to CO2 .
On the other hand the current paper suggests that significant cloud cover changes not due to temperature changes can lead to large swings in climate and temperature. Thus cosmic rays and ocean cycles and possibly other factors could be considerably more important that CO2.
Tallbloke,
You wrote: “if it becomes slightly less negative, it’s still very negative, and overwhelms the effect of changes in co2. ”
No. If cloud forcing becomes less negative in response to warming, it be definition acts as a positive feedback. You’re confused by the reference point. The forcing this paper is discussing is in reference to a cloud free planet: How do clouds affact the radiation balance. You (and Anthony) compare that number to the (surface) forcing by a doubling in CO2. That doesn’t make any sense.
Kev-in-Uk says:
September 20, 2011 at 12:44 pm
John B says:
September 20, 2011 at 12:01 pm
Not so to you too, Sir!
Sorry – but that is the whole illogical basis of the CO2 based AGW theory IMO. It is essentially that a small change in CO2 (a small GHG contributor) causes knock on and supposedly massive changes in other GHG’s water vapour and clouds, etc – but this is simply illogical based on geological past CO2 levels.
————
You are right up until the last part about geological levels. The difference is, in the geological past, CO2 was only a feedback (hence the famous 800 year lag), then humans started burning fossil fuels and CO2 became a forcing. That was the game changer. But don’t take my word for it, get out there and read some science, I think you will find it fascinating.
John B. Why do we have to wait 10 years for Global Warming? Why is it not warming now? Could it be the Sun?? Solar Cycle 24 is in full fail mode.
Please explain why temps are flatlined now and how the IPCC could anticipate that. None of the models anticipated it.
John B says:
September 20, 2011 at 12:52 pm
Haha – I guess I’d best resit all my science exams and give back both my first and masters degrees then?
You are making the classic finger pointing mistake, as per the general warmist argument. You ‘see’ only one metric (CO2) and draw a phenomenal conclusion – conveniently ignoring ALL the other effects. Serious AGW has virtually been disproved based on the lack of continued warming, and of course, alongside all the other revelations….
And I respectfully suggest you need to do some reading and understanding of the relevance of the 800 yr time lag. Temp leads CO2 – this means that logically the (non Anthropogenic) past CO2 increase is an EFFECT – not a cause. No amount of squirming can eliminate that as reasonably well proven fact. As a simple (but slightly silly) counter argument – perhaps we are seeing CO2 rises as a result of warmer temps 800 years ago? How do you KNOW this is not the case?
Dire Wolf says:
September 20, 2011 at 12:55 pm
John B. Why do we have to wait 10 years for Global Warming? Why is it not warming now? Could it be the Sun?? Solar Cycle 24 is in full fail mode.
Please explain why temps are flatlined now and how the IPCC could anticipate that. None of the models anticipated it.
—————-
Yes, it is partly the Sun, partly ENSO, partly who knows what. But the point is, none of those things have a trend. That is why climate scientists are confident warming will resume. Nobody ever predicted a monotonic, year-on-year rise. And the models can’t predict things like La Nina and a quiet Sun, but that is not considered fatal because, as I said, those things don’t show a trend.
Why do we have to wait 10 years? We don’t, but some choose to. The science says warming will resume. You can accept that now or wait until it is blindingly obvious to everyone. I am fast coming to the realisation that the latter is more likely.
As anyone who lives on the wet coast of the Northwest of the USA or wet coast of Canada knows when the clouds come in it gets significantly colder. How any scientist could ever imagine that clouds warm up the atmosphere is beyond the personal experience of most people. Sure the heat is trapped at night as is obvious from clear nights being colder but it’s the blocking of the sun that matters the most. At least that is what is obvious from personal experiences that the vast majority of people living on Earth could tell you. Why haven’t climate scientists gotten this till now? The obvious is non-obvious to agenda driven political climate science? [;)]
Also, is there a comprehensive cloud cover database now that satellite images have been taken for a few decades? It would be interesting to review the statistics of each location where there is a ground thermometer to see what the could cover was over the years. Has anyone done such a study?
Oh, each temperature station should also have a camera pointed skyward to monitor the cloud cover at that specific location, and maybe a camera that could do the same during the day and at night. Also maybe a direct sunlight detector instrument to see if the sun is hitting the temperature station box directly; a light level meter. In addition to all the other sensors.
Also can the heat for all the history of the weather stations be calculated in joules? Have the weather stations across the world kept enough information to compute the heat in joules?
John B
C02 doesn’t suddenly change its physical properties to become a forcing. Perhaps if the atmosphere were dense and 70%+ of it were c02 there may be an argument, but only as a result of air pressure and density as commensurate with the laws of gases.
John B
“You are right up until the last part about geological levels. The difference is, in the geological past, CO2 was only a feedback (hence the famous 800 year lag), then humans started burning fossil fuels and CO2 became a forcing. That was the game changer. But don’t take my word for it, get out there and read some science, I think you will find it fascinating.”
I found it fascinating, until I found that the warmist scientists were lying, hiding data, manipulating the peer review process, and denigrating people instead of doing honest science.(see climategate emails for definative proof)
Then I knew for sure that the warming due to CO2 was going to be a non issue, indeed, beneficial!
“REPLY: Thanks Roy for the clarification. The question of whether clouds act as feedback, forcing, or both is one that will occupy us as a while.”
Clouds are not a forcing. The forcing is radiant energy from the sun. Everything else which responds to that forcing with its own effects is a feedback.
The clouds act as a standard lag-lead compensator to stabilize temperatures.
“Temp leads CO2 – this means that logically the (non Anthropogenic) past CO2 increase is an EFFECT – not a cause.”
YES! In the “non-anthropogenic” past, CO2 increase was an effect. In the past 200 years or so (a) CO2 has gone up far too much to have been an effect from either recent or MWP warming, (b) we are burning fossil fuels and (c) isotope studies show where the added CO2 comes from. Now it is a cause.
But like I said, don’t take my word for it, go and read some mainstream climate science. I may well have got some of the details wrong, so read the experts directly.
Just a quick comment for those who think this the result is obvious.
Ever notice in the winter time, it tends to be warmer on cloudy days and those bright sunny days are the ones where you’ll freeze your butt off? Or that clouds during the night time keep the temperatures from falling as much?
Sometimes what we think is obvious isn’t. That’s why its important to actually do the science. I’m glad these guys did.
P Wilson says:
September 20, 2011 at 1:16 pm
John B
C02 doesn’t suddenly change its physical properties to become a forcing.
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No, it doesn’t. What changed is that for the first time in the history of the planet, masses of the stuff is being released into the atmosphere by the burning of fossil fuels. THAT is why it is now a forcing. Previously, CO2 was added to the atmosphere as a result of some other clamatic event (feedback), now it is a direct result of fossil fuel burning (forcing). But others make the point better than me. Google (or bing) is your friend.
Ed_B says:
September 20, 2011 at 1:17 pm
I found it fascinating, until I found that the warmist scientists were lying, hiding data, manipulating the peer review process, and denigrating people instead of doing honest science.(see climategate emails for definative proof)
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What, all of them? Even Tyndall and Arrhenius in the 19th century? And how about the author of this paper? I guess that depends on whether you like what you think he is saying.
James says:
September 20, 2011 at 4:03 am
…..
‘And cloudy nights would feel colder than clear nights …. oh!’
So are you suggesting that water vapour in clouds retain heat more efficiently on a cloudy night than CO2 does on a clear night ? If so, where does this heat go to?
John B says:
September 20, 2011 at 1:27 pm
This is like taking candy from a baby…..
Look – it’s really simple…if something causes something else to occur – it is a forcing. if the response of the effect is to increase the forcing, then its classed as a positive feedback.. do we agree?
so – if we have had higher temps (which we have) – which we accept subsequently led to higher CO2 (most likely) – and which subsequently were later followed with LOWER temps – what is the likely NET effect of the actual increased CO2?
Even if you do not accept that as a basic analysis – it still demonstrates that CO2 cannot be THE major player (at such low concentrations) because CO2 values were many times higher than today and temps STILL came back down…..
and don’t come back with the rising temps bulldust either – we are still recovering from the last ice age – so obviously temps will be rising (with a superimposed natural cyclical variation)…
I don’t dispute that there may be some effect from the increase in CO2 – but it is so minor as to be insignificant compared to ALL the other effects. You’d be a far better environmental protection advocate to be protesting against deforestation and 3rd world wood burning than coal burning power stations…..
Cloud feedback negative. CLOUD at CERN finds pre-cloud seeds greatly increased by GCRs.
The “Barbarians” (actual scientists using observed data rather than unproven models) are at the gate. Where to run to now?
Dire Wolf says:
Your statement about the models is not really correct. The models do not even attempt to predict all of the jiggles up and down in the global temperature (due to El Nino and La Nina for example). That is because these jiggles are very sensitive to the initial conditions…and hence vary from one run of a model to another. (There has been some recent attempts to try to predict these shorter-term variations, but it is actually a more difficult problem than predicting a long-term trend due to a forcing. This should be of no particular surprise to anyone who thinks much about it: Here in Rochester, nobody would doubt the prediction that the temperature is going to be colder on average this January than it is in July. This is based on the significant change in forcing due to the seasonal cycle. However, a prediction that, say, the temperature trend for the week from October 1-7 will be down or up is considerably more difficult to make, even if we know that ON AVERAGE over several years, we would expect a downward trend because of the seasonal cycle. Likewise, predicting whether this January would be colder or warmer than the average January is also more difficult.)
However, one can look at the statistics of what the models predict and compare it to what we see. For example, how often would the models predict that there would be, say, a 10 year period of no warming when forced with steadily-increasing greenhouse gas forcing? That was investigated in this paper: http://www.leif.org/EOS/2009GL037810.pdf And, the basic answer is that it is not all that unusual to find such periods due to the nature of data that has a slowly increasing trend plus a fair bit of noise.
There may be other contributors to the lower temperature trend over the past decade or so, such as the unusually prolonged sunspot minimum … but there is really as of yet no evidence that it is anything more than the statistical fluctuations that one sees in trends of systems with linear trends + noise over periods of time short enough that the noise is still quite dominant.
coaldust says:
September 20, 2011 at 1:59 pm
Cloud feedback negative. CLOUD at CERN finds pre-cloud seeds greatly increased by GCRs.
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Except that there has been no trend in GCRs, so even if GCRs did cause clouds to form, which is still merely conjecture, it would be irrelevant.
No need to run.
> “REPLY: Dr. Allan, thank you for visiting and for your correction. Please note that I’ve made an update to the post, removing the word negative from the headline and including why I interpreted the paper to demonstrate a negative feedback for clouds. I welcome your thoughts. It seems to me that if clouds had a positive feedback, the dips in 1998 and 2010 in your figure 7 would be peaks rather than deep valleys.”
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El Nino and La Nina are associated with a substantial reorganisation of atmospheric and oceanic circulation and oceanic heat in the top few hundred metres. It would be surprising if clouds did not respond to the rapidly evolving sea surface temperature patterns, yet extracting the cloud feedback processes relevant for global climate change are not so simple.
For example, global temperature anomalies became increasingly positive during 1997 along with positive anomalies in net radation which by your reasoning would be a positive feedback. In fact you can pull out any answer you want if you cherry pick short periods of time and do not consider what is responding to what.
Understanding the physical processes operating during these fluctuations and tracking energy through the climate system, using physical principles, observations and sophisticated models of the atmosphere and oceans, remains an active area of research.
Alcheson says:
September 20, 2011 at 12:48 pm
“For your experiment to be true…. an increase in temperature MUST NOT have much of an effect on cloud cover because the paper in question shows that there is expected to be a huge effect on temperature with only a relatively small change in could cover.”
True dat. But the AGW proponents’ argument does not require the effect to be “much” by your measure. All they require is that the reduction in cloud cover be enough to multiply what would otherwise be the modest temperature response to a CO2 increase–and, as I demonstrated above, even what is apparently not much of an effect by your standards can provide such a multiplication.
The paper does indeed say that clouds have what I view as a large negative effect on surface temperature. But this establishes nothing about how strong the reverse response is: it says nothing about how strongly surface temperature affects clouds.
Now, I personally think that clouds do respond in a negative-feedback way to temperature. (Actually, I find the Eschenbach thermostat theory somewhat compelling, and there’s some controversy about whether that is properly termed a feedback effect.) I also agree that significant components of their variation are essentially independent of surface temperature. I just don’t think this paper sheds much light on those issues.
In any event, my comment above was merely a response to your argument that “[I]f increases in CO2 causes slight warming and the warming leads to fewer clouds . . . then you shouldn’t need any further increase in CO2 to have runaway global warming.” Since this discipline has adopted what to me is a confusing meaning for “positive feedback” (I actually think of it as more a reduction in negative feedback), I doubt that you are the only one who would make that argument. So I provided the thought experiment above to demonstrate that particular argument’s invalidity. I hope it was helpful.
Kev-in-Uk says:
September 20, 2011 at 1:53 pm
John B says:
September 20, 2011 at 1:27 pm
This is like taking candy from a baby…..
Look – it’s really simple…if something causes something else to occur – it is a forcing. if the response of the effect is to increase the forcing, then its classed as a positive feedback.. do we agree?
—————–
Yes, we agree on that, but the rest of your argument doesn’t follow. And the main point is that CO2 can be both a feedback (as it was in the geological past) and a forcing (as it is now). Not because its physical properties changed but because we are now burning fossil fuels whereas we weren’t before. As to whether the effects of anthropogenic CO2 are minor – you have to run the numbers, neither you nor I can conclude anything by handwaving. Go and see what those who have run the numbers conclude.
coaldust says:
September 20, 2011 at 1:59 pm
“CLOUD at CERN finds pre-cloud seeds greatly increased by GCRs.”
Pace my previous comment, one could think of clouds as forcings in this context. But, not really. The GCRs are the forcing here.