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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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What is the net feedback from clouds?

What the science says...

Select a level... Basic Intermediate

Evidence is building that net cloud feedback is likely positive and unlikely to be strongly negative.

Climate Myth...

Clouds provide negative feedback

"Climate models used by the International Panel on Climate Change (IPCC) assume that clouds provide a large positive feedback, greatly amplifying the small warming effect of increasing CO2 content in air. Clouds have made fools of climate modelers. A detailed analysis of cloud behavior from satellite data by Dr. Roy Spencer of the University of Alabama in Huntsville shows that clouds actually provide a strong negative feedback, the opposite of that assumed by the climate modelers. The modelers confused cause and effect, thereby getting the feedback in the wrong direction." (Ken Gregory)

At a glance

What part do clouds play in your life? You might not think about that consciously, but without clouds, Earth's land masses would all be lifeless deserts. Fortunately, the laws of physics prevent such things from being the case. Clouds play that vital role of transporting water from the oceans to land. And there's plenty of them: NASA estimates that around two-thirds of the planet has cloud cover.

Clouds form when water vapour condenses and coalesces around tiny particles called aerosols. Aerosols come in many forms: common examples include dust, smoke and sulphuric acid. At low altitudes, clouds consist of minute water droplets, but high clouds form from ice crystals. Low and high clouds have different roles in regulating Earth's climate. How?

If you've ever been in the position to look down upon low cloud-tops, perhaps from a plane or a mountain-top, you'll have noticed they are a brilliant white. That whiteness is sunlight being reflected off them. In being reflected, that sunlight cannot reach Earth's surface - which is why the temperature falls when clouds roll in to replace blue skies. Under a continuous low cloud-deck, only around 30-60% of the sunlight is getting through. Low clouds literally provide a sunshade.

Not all clouds are such good sunshades. Wispy high clouds are poor reflectors of sunlight but they are very effective traps for heat coming up from below, so their net effect is to aid and abet global warming.

Cloud formation processes often take place on a localised scale. That means their detailed study involves much higher-resolution modelling than the larger-scale global climate models. Fourteen years on, since Ken Gregory of the dubiously-named Big Oil part-funded Canadian group, 'Friends of Science', opined on the matter (see myth box), big advances have been made in such modelling. Today, we far better understand the net effects of clouds in Earth's changing climate system. Confidence is now growing that changes to clouds are likely to amplify, rather than offset, human-caused global warming in the future.

Two important processes have been detected through observation and simulation of cloud behaviour in a warming world. Firstly, just like wildlife, low clouds are migrating polewards as the planet heats up. Why is that bad news? Because the subtropical and tropical regions receive the lion's share of sunshine on Earth. So less cloud in these areas means a lot more energy getting through to the surface. Secondly, we are detecting an increase in the height of the highest cloud-tops at all latitudes. That maintains their efficiency at trapping the heat coming up from below.

There's another effect we need to consider too. Our aerosol emissions have gone up massively since pre-Industrial times. This has caused cloud droplets to become both smaller and more numerous, making them even better reflectors of sunlight. Aerosols released by human activities have therefore had a cooling effect, acting as a counter-balance to a significant portion of the warming caused by greenhouse gas emissions.

But industrial aerosols are also pollutants that adversely affect human health. Having realised this, we are reducing such emissions. That in turn is lowering the reflectivity of low cloud-tops, reducing their cooling effect and therefore amplifying global warming due to rising levels of greenhouse gases.

It sometimes feels as if we are between a rock and a hard place. We'd have been better off not treating our atmosphere as a dustbin to begin with. But there's still a way to fix this and that is by reducing all emissions.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!


Further details

The IPCC's Sixth Assessment Report eloquently sums up where we are in our understanding of how clouds will affect us in a changing climate:

"One of the biggest challenges in climate science has been to predict how clouds will change in a warming world and whether those changes will amplify or partially offset the warming caused by increasing concentrations of greenhouse gases and other human activities. Scientists have made significant progress over the past decade and are now more confident that changes in clouds will amplify, rather than offset, global warming in the future."

The mistake made by our myth-provider, writing in 2009, was to leap to a conclusion without the information needed in order to do so. He is suggesting that clouds are inadequately represented in climate models, so they must have a negative effect on temperatures. Instead of making such leaps of faith, however, the specialists in cloud behaviour have recognised the challenges and met them square-on. We now know a lot more about clouds as a result.

In the at-a-glance section, we explain the important difference between high clouds and low clouds, agents of warming and cooling respectively. Careful examination of older satellite records has detected large-scale patterns of cloud change between the 1980s and 2000s (Norris et al. 2016). Observed and simulated cloud change patterns are consistent with the poleward retreat of midlatitude storm tracks, the expansion of subtropical dry zones and increasing height of the highest cloud tops at all latitudes. The main drivers of these cloud changes appear to be twofold: increasing greenhouse gas concentrations and recovery from volcanic radiative cooling. As a result, the cloud changes most consistently predicted by global climate models have indeed been occurring in nature.

With respect to the cooling low clouds, one particularly important area of study has involved marine stratocumulus cloud-decks. These are extensive, low-lying clouds with tops mostly below 2 km (7,000 ft) altitude and they are the most common cloud type on Earth. Over the oceans, stratocumulus often forms nearly unbroken decks, extending over thousands of square kilometres. Such clouds cover about 20% of the tropical oceans between 30°S and 30°N and they are especially common off the western coasts of North and South America and Africa (fig.1). That's because the surface waters of the oceans are pushed away from the western margins of continents due to the eastwards direction of Earth's spin on its axis. Taking the place of these displaced surface waters are upwelling, relatively cool waters from the ocean depths. The cool waters serve to chill the moist air above, making its water vapour content condense out into cloud-forming droplets.

 Satellite image of stratocumulus clouds.

Fig. 1: visible satellite image of part of an extensive marine stratocumulus deck off the western seaboard of North America, with Baja California easily recognisable on the right. Image: NASA.

With their highly reflective tops that block a lot of the incoming sunlight, the marine stratocumulus clouds have a very important role as climate regulators. It has long been known that increasing the area of the oceans covered by such clouds, even by just a few percent, can lead to substantial global cooling. Conversely, decreasing the area they cover can lead to substantial global warming.

Although many cloud-types are produced by convection, driven by the heated land or ocean surface, marine stratocumulus clouds are different. They are formed and maintained by turbulent overturning circulations, driven by radiative cooling at the cloud tops. It works as follows: cold air sinks, so that radiatively-cooled air makes its way down to the sea surface, picks up moisture and then brings that moisture back up, nourishing and sustaining the clouds.

Stratocumulus decks can and do break up, though. This happens when that radiative cooling at the cloud tops becomes too weak to send colder air sinking down to the surface. It can also occur when the turbulence that can entrain dry and warm air, from above the clouds into the cloud layer, becomes too strong.

The importance of such processes has been further investigated recently, using an ultra-high resolution model with a 50-metre grid size. (Schneider et al. 2019). Global climate models typically have grid sizes of tens of kilometres. At that resolution, they cannot detail such fine-scale processes. This model, by contrast, is able to resolve the individual stratocumulus updraughts and downdraughts.

 Results of modelling of marine stratocumulus behaviour.

Fig. 2: results of modelling of marine stratocumulus behaviour in a high-CO2 world. This one compares conditions at 400 ppm (present) and 1600 ppm (hopefully never, but relevant to the Palaeocene and Eocene when a super-Hothouse climate prevailed). Redrawn from Schneider et al. 2019.

The modelling shows how oceanic stratocumulus decks become unstable and break up into scattered cumulus clouds. That occurs at greenhouse gas levels of around 1,200 ppm (fig. 2). When that happens, the ocean surface below the clouds warms abruptly because the cloud shading is so diminished. In the model, the extra solar energy absorbed as stratocumulus decks break up, over an area estimated to cover about 6.5% of the globe, is enough to cause a further ~8oC of global warming. After the stratocumulus decks have broken up, they only re-form once CO2 levels have dropped substantially below the level at which the instability first occurred.

These results point to the possibility that there is a previously undiscovered, potentially strong and nonlinear feedback, lurking within the climate system. These findings may well help to solve certain palaeoclimatic problems, such as the super-Hothouse climate of the Palaeocene-Eocene, some 50 million years ago. It's been hard to fully explain that event, given that estimates of CO2 levels at the time do not exceed 2,000 ppm. Present climate models do not reach that level of warmth with that amount of CO2. But the fossil record presents hard evidence for near-tropical conditions in which crocodilians thrived - in the Arctic. Something brought about that climate shift!

The quantitative aspects of stratocumulus cloud-deck instability remain under investigation. However the phenomenon appears to be robust for the physical reasons described by Schneider and co-authors. Closer to the present, the recent acceleration of global warming may be partly due to a decrease in aerosols. Aerosols produce smaller and more numerous cloud droplets. These have the effect of increasing the reflectivity and hence albedo of low cloud-tops (fig. 3). It follows that if aerosol levels decrease, the reverse will be the case. Of considerable relevance here are the limits on the sulphur content of ship fuels, imposed by the International Maritime Organization in early 2015. These regulations were further tightened in 2020. An ongoing fall in aerosol pollution, right under the marine stratocumulus decks, would be expected to occur. As a consequence, the size and amount of cloud droplets would change, cloud top albedo would decrease and there would be increased absorption of solar energy by Earth. That would be on top of the existing greenhouse gas-caused global warming. James Hansen discussed this in a recent communication (PDF) here.

Cloud effects on Earth's radiation.

Fig. 3: NASA graphic depicting the relationship between clouds, incoming Solar radiation and long-wave Infrared (IR) radiation. High clouds composed of ice crystals reflect little sunlight but absorb and emit a significant amount of IR. Conversely low clouds, composed of water droplets, reflect a great deal of sunlight and also absorb and emit IR. Any mechanism that reduces low cloud-top albedo will therefore increase the sunlight reaching the surface, causing additional warming.

In their Sixth Assessment Report, the IPCC also points out that the concentration of aerosols in the atmosphere has markedly increased since the pre-industrial era. As a consequence, clouds now reflect more incoming Solar energy than before industrial times. In other words, aerosols released by human activities have had a cooling effect. That cooling effect has countered a lot of the warming caused by increases in greenhouse gas emissions over the last century. Nevertheless, they also state that this counter-effect is expected to diminish in the future. As air pollution controls are adopted worldwide, there will be a reduction in the amount of aerosols released into the atmosphere. Therefore, cloud-top albedo is expected to diminish. Hansen merely suggests this albedo-reduction may already be underway.

Last updated on 15 October 2023 by John Mason. View Archives

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Argument Feedback

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Additional viewing

To explore this complex topic further, this is a great TED talk by climate scientist Kate Marvel:

Denial101x video(s)

Here is the relevant lecture-video from Denial101x - Making Sense of Climate Science Denial

Additional video from the MOOC

Expert interview with Steve Sherwood

Comments

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Comments 51 to 75 out of 159:

  1. RW1 - Re: your claim that "A very large amount (if not most) of the enhanced warming from the climate models comes from positive cloud feedback." From your link: "In AOGCMs, the water vapour feedback constitutes by far the strongest feedback" - followed by the lapse rate, and then surface albedo and clouds. "Water vapor and clouds act on time scales of hours to days." Absolutely. Which why they are strictly feedbacks, not forcings. They cannot stay out of balance long enough to affect any other feedbacks on their own.
  2. Sphaerica (RE 48), "Water vapor does not equal clouds." I never claimed that it did. "Again, no, clouds come in a distant fourth, at best, behind H2O feedbacks (water vapor), CO2 feedbacks, and albedo feedbacks." Not according the latest IPCC report, which says: "The water vapour feedback is, however, closely related to the lapse rate feedback (see above), and the two combined result in a feedback parameter of approximately 1 W m–2 °C–1, corresponding to an amplification of the basic temperature response by approximately 50%. The surface albedo feedback amplifies the basic response by about 10%, and the cloud feedback does so by 10 to 50% depending on the GCM." Clouds can be up to 50%, where as surface albedo is only about 10%.
  3. KR (RE: 51), "From your link: "In AOGCMs, the water vapour feedback constitutes by far the strongest feedback" - followed by the lapse rate, and then surface albedo and clouds." Are you not actually reading the whole section? This not what it says (or implies). The surface albedo is the smallest feedback - closer to a third of the average cloud feedback (0.26 W m-2 °C–1 vs. 0.69 W m–2 °C–1 for clouds). The water vapor feedback is directly tied to and offset by the lapse rate feedback (1.80 W m-2 °C–1 vs. -0.84 W m-2 °C–1 for the lapse rate). " 'Water vapor and clouds act on time scales of hours to days.' Absolutely. Which why they are strictly feedbacks, not forcings." Define specifically what you mean by a 'forcing'? The only true 'forcing' of the climate system is the Sun. All the other components, such as water vapor, clouds, and precipitation, are really just responding directly or indirectly to the Sun's forcing, the net effect of all of which dictate the equilibrium surface temperature. "They cannot stay out of balance long enough to affect any other feedbacks on their own." Why not? What's keeping them from staying "out of balance"?
  4. muoncounter (RE: 50), "Huh? What does that have to do with the rate at which CO2 radiative forcing increases global temperature?" I don't understand the question. Is 100 years not a significantly slower rate than hours to days?
  5. See the IPCC report for formal definition of forcing, but it is basically something can change the radiative balance independent of temperature. Only a change in forcing can change climate. The forcing in the system are solar, GHGs (which can also be a feedback, but are a forcing if changed independently of temperature -eg by release of fossil fuel), and aerosols. On a larger time scale, changes in continent distribution and in the nature of the biosphere can alter albedo so that it is also a forcing.
  6. KR (RE: 51), If water vapor is not a 'forcing' in the climate system, then how can CO2 be a 'forcing'? Are you claiming that increased water vapor in the atmosphere is not a 'forcing', but increased CO2 is a 'forcing'? This is the problem. They are both 'forcings' in the way you're using the term. The main difference is water vapor acts on much shorter time scales, but it is still a 'forcing' none the less.
  7. 52, RW1, Clouds come in ahead of albedo, and behind water vapor. I'm still not quite sure how you turn this into "A very large amount (if not most) of the enhanced warming" but I'll concede the point. Clouds are an important positive feedback in the models (but not "most"). So what's your point? 53, RW1,
    The only true 'forcing' of the climate system is the Sun.
    No. If anything, solar output is the single strongest constant in the entire system. Changes in CO2 concentrations in the atmosphere are almost certainly the primary driver as far as total change. They are tied to every major climate swing in some way, and global temperature closely tracks CO2 concentrations. Albedo is probably the primary driver as far as getting the ball rolling (and that can come from orbital forcings or aerosols -- volcanism). Water vapor and clouds are fast acting feedbacks that do not force anything on their own. But we're drifting. What is your point about clouds again? Now that you've proven that they are a strong positive feedback, why are we discussing them?
  8. 56, RW1,
    ...but increased CO2 is a 'forcing'?
    Yes, because water vapor responds quickly to changes in temperature. There's nothing anyone or anything can do to inject water vapor into the atmosphere and keep it there. The temperature will drop, and the water vapor will condense and things will return to normal. This is not the case with CO2, whether it is added anthropogenically or geologically. No matter how it gets there, once it does get there, it stays there for a very long time and it's effect forces the climate to follow suit.
  9. RW1 - "If water vapor is not a 'forcing' in the climate system, then how can CO2 be a 'forcing'? Are you claiming that increased water vapor in the atmosphere is not a 'forcing', but increased CO2 is a 'forcing'?" Not just claiming that, but stating that with plenty of evidence. CO2 has been changing due to anthropogenic emissions, while water vapor and clouds have been changing strictly due to temperature changes. This is part of the grand scheme of Cause -> Effect, RSVP; CO2 (due to our actions) is a recent cause of climate change, water vapor and clouds respond as an effect.
  10. RW1#54: "I don't understand the question." Well, you stated "Anthropogenic CO2 forcing is very gradual," I asked how you to substantiate this; you responded that "it's claimed to take about 100 years to double CO2." The time it takes to double CO2 through anthropogenic input has nothing to do with the time it takes for the forcing of CO2 already in the atmosphere to increase temperature, which is, of course, already in progress. I don't understand how you mixed up the two. See the 40 year lag thread I linked earlier for discussion of this.
  11. Sphaerica (RE: 57), "What is your point about clouds again? Now that you've proven that they are a strong positive feedback, why are we discussing them?" Because if a lot of the enhanced warming comes from positive cloud feedback, and the cloud feedback is NOT really positive - but negative (even slightly negative), it is going to reduce the projected amount of warming significantly. The IPCC even says that if the cloud feedback is neutral, it would reduce the average sensitivity to 1.9 C instead of 3 C. That's a reduction of over half of the enhanced warming. If the cloud feedback was even moderately negative, the average sensitivity could easily come down to 1 C or less. In short, the cloud feedback is huge.
  12. muoncounter (RE: 60), "The time it takes to double CO2 through anthropogenic input has nothing to do with the time it takes for the forcing of CO2 already in the atmosphere to increase temperature, which is, of course, already in progress. I don't understand how you mixed up the two. See the 40 year lag thread I linked earlier for discussion of this." Sorry for the misunderstanding, but my question then is why doesn't it take 40 years for the forcing of water vapor in the atmosphere to increase (and decrease) temperature?
  13. RW1#62: "why doesn't it take 40 years for the forcing of water vapor in the atmosphere" I thought there was agreement that water vapor doesn't stay in the atmosphere that long. I don't know how things are where you live, but I wipe a lot of that water vapor off my car windows every morning. #61: "the average sensitivity could easily come down to 1 C or less." Ah, we've come full circle, as you've said that before: It's also inline with the sensitivity only being about 0.6 C . Of course, the temperature record doesn't support that contention, as we've already seen 0.8C with far less than a doubling of CO2.
  14. KR (RE: 59), "Not just claiming that, but stating that with plenty of evidence. CO2 has been changing due to anthropogenic emissions, while water vapor and clouds have been changing strictly due to temperature changes." Not necessarily strictly temperature changes, but even so, I don't see how that excludes them from being a 'forcing'. Do water vapor changes not also cause temperature changes? Do cloud changes not also cause temperature changes? Surely they do.
  15. muoncounter (RE: 62), "I thought there was agreement that water vapor doesn't stay in the atmosphere that long." It doesn't, but it also doesn't take 40 years for changes in water vapor concentration to effect changes in temperature. For example, a sunny humid day is generally warmer than a sunny dry day, all other things being equal. "Ah, we've come full circle, as you've said that before: It's also inline with the sensitivity only being about 0.6 C" That was assuming only half of the 3.7 W/m^2 from 2xCO2 is incident on the surface. For the purposes of this discussion and elsewhere here, I've accepted that the full 3.7 W/m^2 affects the surface (at least for now).
  16. RW1 - At the risk of repeating myself: Cause => Effect CO2 is a cause, changing (primarly and from anthropogenic actions) independent of temperature, while water vapor and clouds respond promptly to temperature and don't change on their own, and are hence amplifying effects of temperature change. Water vapor and clouds change in response to temperature. If you have any evidence supporting water vapor or cloud changes independent of temperature, I suggest you publish it. Nobody else has found any such evidence - I will (I believe correctly) take assertions to that effect as just wishful thinking without such evidence.
  17. RW1 - clouds are not forcing because unless you have something like GCR changing clouds, there is no way to produce a long term change in cloud cover without something else being responsible for changing the temperature. If your vision of reality is right, then you would have world with no change to GHG, solar, or aerosols, going through climate change (ie a long term change in radiative balance). Now plenty of that kind of internal variability in short time scales - weather. But no evidence whatsoever of any such change on long term.
  18. Sphaerica (RE: 58), "Yes, because water vapor responds quickly to changes in temperature. There's nothing anyone or anything can do to inject water vapor into the atmosphere and keep it there. The temperature will drop, and the water vapor will condense and things will return to normal." But what causes the temperature to drop and the water vapor to be removed from the atmosphere if water vapor is the primary amplifier of warming? "This is not the case with CO2, whether it is added anthropogenically or geologically. No matter how it gets there, once it does get there, it stays there for a very long time and it's effect forces the climate to follow suit." Yes, but I don't see how CO2's effect is fundamentally different than water vapor, especially if water vapor is the primary amplifier of warming (CO2 induced or otherwise). In other words, why would the response to water vapor warming in the system be any different than warming caused by CO2? Why would the same forces that modulate or control water vapor's radiative forcing, not modulate and control CO2's radiative forcing? The surface has no way of distinguishing where the radiative 'forcing' originated from - water vapor or CO2. All the surface 'knows' is its total energy flux, as it determines the surface temperature.
  19. The atmosphere has a temperature gradient. At a certain height, water condenses out. CO2 does not. Maximum water content in atmosphere is temperature-dependent. Maximum CO2 is not. Note that in our current AGW-world, CO2 is not a feedback. The mechanisms are too slow to have produced much GHG feedback yet.
  20. scaddenp (RE: 69), "The atmosphere has a temperature gradient. At a certain height, water condenses out. CO2 does not." I know. "Note that in our current AGW-world, CO2 is not a feedback." Agreed.
  21. RW1,
    In short, the cloud feedback is huge.
    You love to exaggerate things. The cloud feedback is important, not huge. It's more important if it is neutral or negative, but you've shown no evidence other than that you think common sense says so, while hundreds of climate scientists think otherwise. But even if you proved clouds to be a weak negative feedback, it would reduce sensitivity to anywhere from 1.9 to 3.4 (versus 3 to 4.5), given that 3 is the current best estimate, but also at the low end of the range. Even 1.9 is very, very bad, especially since we're currently taking no action to avoid it. But first you need to submit some evidence beyond your "plain, everyman logic" to prove that clouds are even a neutral feedback, let alone negative. And that evidence has to contradict all of this evidence to the contrary. I'm afraid a sensitivity below 3˚C is very, very unlikely.
    But what causes the temperature to drop and the water vapor to be removed from the atmosphere if water vapor is the primary amplifier of warming?
    This question is evidence that you don't understand how things work. You need to go study more. If this were the case, the planet would never, ever cool, no matter what.
    ...but I don't see how CO2's effect is fundamentally different than water vapor..
    Because water vapor will increase or decrease in the atmosphere fairly quickly in response to temperature. Raise the temperature, raise the water vapor. Lower the temperature, lower the water vapor. CO2, on the other hand, will stay in the atmosphere for hundreds of years, even if, for example, a large volcanic eruption temporarily lowers temperatures.
    ...why would the response to water vapor warming in the system be any different than warming caused by CO2?
    There's no difference in the warming. What is different is that the CO2 won't drop out of the atmosphere when the temperature drops (for instance, during the winter).
    Why would the same forces that modulate or control water vapor's radiative forcing, not modulate and control CO2's radiative forcing?
    There are no such forces for either. This isn't a human designed system with controls and balances. It's nature, and it's (fortunately) got a simple balance to it, and one that should be very hard to shove, but we've found a way to do it. The point is not how each one (water vapor vs. CO2) affects temperature. The point is that water vapor content is itself affected by temperature on short time scales, while CO2 is only affected on very, very long time scales. And, in fact, there is a positive CO2 feedback (such as outgassing from the ocean) that will, in the long term, increase CO2 levels even further.
  22. KR (RE: 66), "Cause => Effect CO2 is a cause, changing (primarly and from anthropogenic actions) independent of temperature, while water vapor and clouds respond promptly to temperature and don't change on their own, and are hence amplifying effects of temperature change." I think the confusion here lies somewhere in between the definition of 'forcing' and that there are many other things in the climate system, other than anthropogenic CO2 (and GHGs), that are changing and subsequently inducing new 'forcings' independent of temperature. As just one example, take the fluctuations of Arctic and Antarctic sea ice extents, which we know are largely driven by factors other than temperature (wind patterns, ocean currents, etc,). Yes, anthropogenic CO2 'forcing' is a cause and not an effect of temperature, but even without anthropogenic CO2, the climate is frequently perturbed by new 'forcings' - not all of which are due to temperature changes, yet the globally averaged temperature remains very, very stable.
  23. RW1 - the answer then to "Yes, but I don't see how CO2's effect is fundamentally different than water vapor, especially if water vapor is the primary amplifier of warming (CO2 induced or otherwise)." CO2 is non-condensated gas. That is why the same forces that modulate or control water vapor's radiative forcing, do not modulate and control CO2's radiative forcing.
  24. "As just one example, take the fluctuations of Arctic and Antarctic sea ice extents, which we know are largely driven by factors other than temperature (wind patterns, ocean currents, etc,). " Splorff! Long term (30 year) change in arctic albedo is driven ultimately by change in temperature. Short term variation from year to year depends on wind/ocean etc. Oh and what is changing ocean/wind? I think it is time to come up with some evidence for unforced climate change if you are arguing about the definition of forcing.
  25. RW1 wrote: "I think the confusion here lies somewhere in between the definition of 'forcing' and that there are many other things in the climate system, other than anthropogenic CO2 (and GHGs), that are changing and subsequently inducing new 'forcings' independent of temperature. As just one example, take the fluctuations of Arctic and Antarctic sea ice extents, which we know are largely driven by factors other than temperature (wind patterns, ocean currents, etc,)."
    What boils to: - I know it is a system - I know CO2 is a factor - But the cause must be elsewhere, darn. - Let me uncouple the system and I'll tell why. Let also that the uncoupling makes Temperature an irrelevant variable to the climate system. "Why would you stop when you can rev up?" (signed: Thelma & Louise)

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