Will water vapor be a positive or negative feedback?

Regardless of whether people find Lindzen's hypothesis compelling or not, more objective analysis of the concept has shown that Lindzen used unrealistic assumptions in his original work in order to get a significant Iris effect. See here:

http://www.atmos-chem-phys.net/2/31/2002/acp-2-31-...

Furthermore, if you just do a back-of-the-envelope calculation (see note 1 below) on how much deep convection would have to increase, either in areal extent or in intensity, to offset the global radiative forcing from CO2, it comes out to be something on the order of 40%. This means that the mean latent heat flux from the ocean to the air has to increase from 100 W/m^2 (the rough global average) to 140 W/m^2. That is a *huge* increase (equivalent to mean surface wind speed increasing by around 40%), and one that is simply not seen in the data (see note 2 below).

In short, unless you are emotionally invested in wanting to believe Lindzen is correct, objective analysis would suggest that water vapor is a positive feedback. It is also important to consider that Lindzen came up with the Iris effect as a justification for why there would be no increase in global temperature as CO2 increased. Of course, temperature has increased because of CO2, which ought to make one very suspicious of claims it will kick in as a negative forcing anytime soon.

Warming of the ocean and water vapour effects are still poorly understood and not well represented in the IPCC’s models by their own admission.

The relationship between the various functions are complex. There is also the Svensmark theory that cosmic rays help seed cloud formation adding another factor to the system. The effect of cosmic rays on cloud cover has now been confirmed with practical tests, suggesting this theory may well be correct.

So the process is very complex and is currently poorly understood.

Clouds being able to cool the climate is evident when cloud cover moves in during a sunny day, I recall watching the temperature drop from 25 to around 16 degrees over a 2 hour period recently during such an event.

Personally I believe that water vapour has a general warming effect (especially at night) which fed by sea temperatures and works to stabilise the earths temperature between the contrast of night and day. This is most evident in dry climates where the difference between night and day is far more pronounced.

There is of course an equilibrium point at which as much energy is reflected by water vapour than is trapped, thus preventing any further warming, otherwise during much warmer periods in the past the earth would have entered a “runaway” warming scenario. This is similar to the physics of co2, were its potential warming ability reduces exponentially as it increases in the atmosphere, with the first 20ppm absorbing the most long wave energy.

This is why runaway greenhouse warming did not occur during the Cambrian era when co2 was around 7000ppm when the earth was only 7 degrees warmer (IPCC, 2001) with most the warmth caused by solar forcing (as there were no humans then).

Note that the above paper is contradicted by other studies, and only one can be right!

Also, since the warming effect of water vapour is as much a natural feedback as it is a potential feedback from man made co2, this provides no support for AGW. As only 3% of co2 is human produced, 97% is therefore natural, meaning around 110ppm of the co2 rise this centuary has been natural, most likely caused by warming of the sea, as may be the increased water vapour.

Try and keep an open mind as the science is far from settled!

Report of Svensmark's practical test confirming solar influence:

http://www.spacedaily.com/reports/Exploding_Stars_...

As usuall the assumed understanding of Earths energy budget is way off base, to make the statement:

""""The analysis concludes "The existence of a strong and positive water-vapor feedback means that projected business-as-usual greenhouse-gas emissions over the next century are virtually guaranteed to produce warming of several degrees Celsius. The only way that will not happen is if a strong, negative, and currently unknown feedback is discovered somewhere in our climate system.""""

is simply a naive and foolish statement. considering that the amount of water vapor in the global atmosphere is regulated by ocean surface temperature cycles such as the PDO. The radiative properties of earths atmosphere will be altered substantially more than even a doubling of atmospheric CO2.

New research and computer models that model the PDO and the associated atmospheric radiative transfer changes that the PDO would modulate can account for 66% of the global warming over the 20th century.

The planet has not warmed for several years, and 'SCIENCE' predicts that it will cool significantly for decades to come, that is just a few of my thoughts about water vapor as a feedback.

It is not just Lidzen, it is also Roy Spensor. To quote his own words:

Our paper "Potential Biases in Feedback Diagnosis from Observational Data: A Simple Model Description" will appear in the November 1, 2008 issue of Journal of Climate. It demonstrates how non-feedback variations in cloud cover cause a low bias in feedbacks diagnosed from satellite data, resulting in the illusion of a climate system more sensitive than it really is.

While the paper uses the simple example of daily random cloud fluctuations, the basic issue of non-feedback cloud fluctuations has huge consequences for global warming theory. Any change in global cloudiness associated with a low frequency mode of natural variability in the general circulation of the ocean-atmosphere system (e.g., the Pacific Decadal Oscillation) would cause internal radiative forcing which could lead to substantial long-term temperature variability...even "global warming". From what I can tell, the IPCC has ignored this possibility.

This internal radiative forcing has a unique "fingerprint" that distinguishes it from radiative feedback on temperature: radiative forcing 'spirals' versus 'stripes'. We have also found this signature of internal radiative forcing in most of the IPCC climate models, so it can not be claimed by modelers that such internal radiative forcing does not exist.

October 8, 2008 RESEARCH UPDATE #2:

We have submitted a paper for publication to Geophysical Research Letters entitled, "Satellites Reveal a Climate System Less Sensitive than in Models". This paper should answer the previous criticisms of our August 2007 GRL paper on negative feedback in the tropics that (1) it only applied to the the tropics, and (2) that feedbacks diagnosed on short time scales might not apply to long-term global warming.

In the new paper we diagnose feedback parameters from 5 years of NASA Aqua satellite data over the global oceans AND perform exactly the same diagnoses on all possible 5-year periods in transient CO2 simulations from 18 IPCC climate models.

The results are, as you can see below, (see here: http://www.weatherquestions.com/Roy-Spencer-on-glo... somewhat stunning...NONE of the five year periods from ANY of the IPCC climate models show the negative feedback behavior seen in the satellite data:

Contrary to my expectations, though, the negative feedback was not in the longwave (infrared); there was an excellent match between the models and satellite observations in that component, suggesting that the total [water vapor + lapse rate + high cloud] LW feedback was weakly positive.

Instead, the negative feedback was entirely in the reflected shortwave (solar)...suggesting that low clouds increase with warming. This is actually somewhat consistent with the IPCC AR4 report which admitted that feedbacks related to low cloud behavior were the most uncertain in the models. Since this is an apples-to-apples comparison between the models and the satellite observations, it will be difficult for the IPCC to ignore this kind of evidence.

The question of WHY the IPCC models would be so far off is, in my view, related to what I discussed above, in my Research Update #1: In previous analyses of natural co-variability between clouds and temperature, only feedback has been assumed to be operating, when in fact some of the variability is actually cloud fluctuations causing temperature change. In simple terms, there has been a mix-up between cause and effect, and that has led to climate models being built upon faulty assumptions.

Now, if the modelers STILL insist that this short term (5-year) feedback behavior -- even in the models -- does not invalidate positive feedback for long-term global warming, I will respond: "OK, then adjust the models so they behave like the satellite observations on the short (5-year) time scale, and THEN show us how much global warming the models predict".

Lindzen demonstrated that adding heat will cause an "Iris Effect" which buffers the temperature. With increasing temperature, fewer cirrus clouds would form, allowing more heat out. You would do a disservice to yourself if you don't look at Lindzen's arguments rather than how they are spun. Clearly, we don't understand the water vapor system and what exactly governs how much water vapor is in the atmosphere. All alarmists will look at are positive feed backs since negative feed backs tend to lesson the effects of any warming. I find Lindzen's arguments interesting and compelling. I am sure they are like sacrilege to an alarmist.

There is some problems. Water has a refrigeration effect. Each cc of water that evaporates will absorb 60 calories. That is quite a cooling effect. The high clouds reflect a lot of sun light back into space.

It will do both. The NET effect is what is important. The system is simply too complex to give a firm number or direction to the effect. Models have given both answers.

It makes sense--in fact it's really a no-brainer (which explais the "skeptics" contrary view!).

Here's why. When water vapor forms clouds, it does indeed reflect heat back into space--and that creates a cooling effect.

HOWEVER, most of the water vapor in the atmosphere at any given time is NOT in the form of light reflecting clouds. But it acts as a green house gas all of the time.

So, as temperatures rise, we get more water vapor in the atmosphere-and more clouds. But again--most ofthat water vapor,most of the time, isn't in a cloud and isn't reflecting an y sunlight or heat. It's trapping heat a a greenhouse gas.

As no one is really sure what causes clouds to form, no one could know.

The question shouldn't be the feedback or not of vapor, but the creation or not of clouds.

The sunspot theory has more to say about cloud formation, and sunspot theory says fewer sunspots, more low clouds, which will create cooler conditions on the earth.

i understood that high cloud bad, low cloud good as far as you can generalise. therefore i do worry on days like yesterday, where the whole sky here was covered in a net of cirrus clouds, all of which as far as i could see had started with con. trails. (we about 50miles from heathrow)