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#23907 10/17/07 08:29 PM
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I felt that water vapour and clouds needed a topic of its own. In the http://www.scienceagogo.com/forum/ubbthreads.php?ubb=showflat&Number=23878#Post23878 post, Chris said the following:

Originally Posted By: Chris
Just as a response to some points above- on the feedbacks, I think I already went over this, but the inseparable water and clouds is a falsehood. First, the cooling due to evaporation is how the surface comes back to equilibrium after being perturbed by the increased radiative heating; that is automatically accounted for in models, and is necessary for them to reach equilibrium, which is a prerequisite for an estimate of the "equilibrium climate sensitivity" to a doubling of CO2 that is always cited from the IPCC reports (i.e., 1.5-4.5 deg. C until the most recent report, now 2-4.5 is more like it). Then, it is not true that increased evaporation forms clouds and is an example of a negative feedback. Increased evaporation increases water vapor; the competition between increased water vapor and increased temperature cause relative humidity to change little as the climate warms (you need saturation to get a cloud), and it is relative humidity that determines the formation of clouds. As proof: In midlatitudes it's a lot warmer in summer than winter, and there's lots more evaporation in summer, yet if anything there are fewer clouds because relative humidity is on average lower. But Climate models now predict that cloud feedback will be either close to neutral or positive in a warmer climate.


Ignoring that I was misquoted as suggesting that water and clouds are inseparable instead of water <b>vapour</b> and clouds, there is some discussion worthy ideas in his quote.

"the competition between increased water vapor and increased temperature cause relative humidity to change little as the climate warms" The only way to have a competition like you describe is within a closed system. The earth is not a closed system. As the sun warms us in the morning, the relative humidity goes down. It drops about 4% per degree Celcius of temp increase.

"...it is relative humidity that determines the formation of clouds." This is not true. While you are right when you said that "you need saturation to get a cloud," relative humidity is just a measurement. It determines nothing. Usually the most important factor is pressure. More specifically, it is the weather pressure system that is above the area that will determine weather or not clouds will form.

What affects cloud formation is condensation due to a temperature change. This is most common when we are in a low pressure system that allows the humid surface air to rise and cool. When we are in a high pressure system, then the warm humid surface air is not able to rise. We get clear skies when the pressure rises. This is just the most common. Anyone who has seen storm clouds roll in has witness a warm and a cold front colliding, but that is not as common that I have seen in Ontario.

The discussion about mid-latitudes is wrong since it suggests that temperature determines clouds alone. That is not the case. The key is temperature change. It is the ability for air to rise to the cooler high troposphere. How do I know? I live at a mid latitude (46.6 N). This summer we had back to back low pressure systems in July such that we had a tonne of clouds and near record rainfall.

Finally, for some reason, the "[b]ut Climate models now predict that cloud feedback will be either close to neutral or positive in a warmer climate." line was tagged to the end. When I am walking home at lunch on a mostly cloudy day, I appreciate the few breaks in the clouds. It is those few sunny breaks that warm my face nicely until the next cloud gets in the way. While cloud cover at night will keep some heat in such that dew or frost will not form, clouds during the day repel a lot of nice heat on an otherwise cold and cloudy day. If climate models are predicting the opposite, then their output does not make sense.

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Is it just me, or does every significant temperature feedback seem to be positive (according to our 'present knowledge')?
If that were the case and there really was no significant negative feedbacks to offset the positive ones, wouldn't you expect that the earth would have experienced a runaway greenhouse effect at some point in it's history?

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John, we're talking about two different things- you're speaking of diurnal variation and I'm speaking of climatic (larger scales of time and space) of feedbacks, and how a warmer climate and water vapor and clouds will interact if the world were to get warmer- I know very well that morning and night change; when talking about this in the context of global warming we're referring to how water vapor in the atmosphere or how cloud feedbacks will effect global mean temperature on decadal scales. To put this in perspective, abstract from Willett et al (2007):

Quote:
Letter
Nature 449, 710-712 (11 October 2007) | doi:10.1038/nature06207; Received 29 March 2007; Accepted 30 August 2007


Attribution of observed surface humidity changes to human influence
Water vapour is the most important contributor to the natural greenhouse effect, and the amount of water vapour in the atmosphere is expected to increase under conditions of greenhouse-gas-induced warming, leading to a significant feedback on anthropogenic climate change. Theoretical and modelling studies predict that relative humidity will remain approximately constant at the global scale as the climate warms, leading to an increase in specific humidity1. Although significant increases in surface specific humidity have been identified in several regions, and on the global scale in non-homogenized data, it has not been shown whether these changes are due to natural or human influences on climate. Here we use a new quality-controlled and homogenized gridded observational data set of surface humidity, with output from a coupled climate model, to identify and explore the causes of changes in surface specific humidity over the late twentieth century. We identify a significant global-scale increase in surface specific humidity that is attributable mainly to human influence. Specific humidity is found to have increased in response to rising temperatures, with relative humidity remaining approximately constant. These changes may have important implications, because atmospheric humidity is a key variable in determining the geographical distribution11, 12, 13 and maximum intensity14 of precipitation, the potential maximum intensity of tropical cyclones15, and human heat stress16, and has important effects on the biosphere17 and surface hydrology17, 18.


and what I've already went over:

we have data that show that overall low clouds, which control the albedo more than any other kind, get thinner when it gets warmer. There are many different cloud types and effects, but they won't have much impact.

Some papers on specific feedback questions that can be found at http://pubs.giss.nasa.gov/ include

Bony, S., R. Colman, V.M. Kattsov, R.P. Allan, C.S. Bretherton, J.-L. Dufresne, A. Hall, S. Hallegatte, M.M. Holland, W. Ingram, D.A. Randall, D.J. Soden, G. Tselioudis, and M.J. Webb, 2006: How well do we understand and evaluate climate change feedback processes? J. Climate, 19,3445-3482, doi:10.1175/JCLI3819.1.

Tselioudis, G., and W.B. Rossow, 2006: Climate feedback implied by observed radiation and precipitation changes with midlatitude storm strength and frequency. Geophys. Res. Lett., 33, L02704, doi:10.1029/2005GL024513.

Tselioudis, G., and W.B. Rossow, 1994: Global, multiyear variations of optical thickness with temperature in low and cirrus clouds. Geophys.Res. Lett., 21, 2211-2214, doi:10.1029/94GL02004.

Naud, C., A.D. Del Genio, and M. Bauer, 2006: Observational constraints on cloud thermodynamic phase in midlatitude storms. J. Climate, 19, 5273-5288, doi:10.1175/JCLI3919.1.

Del Genio, A.D., W. Kovari, M.-S. Yao, and J. Jonas, 2005: Cumulus microphysics and climate sensitivity. J. Climate, 18, 2376-2387, doi:10.1175/JCLI3413.1.

Del Genio, A.D., 2002: The dust settles on water vapor feedback. Science, 296, 665-666, doi:10.1126/science.1071400.

Del Genio, A.D., and A.B. Wolf, 2000: The temperature dependence of the liquid water path of low clouds in the southern Great Plains. J.Climate, 13, 3465-3486, doi:10.1175/1520-0442(2000)

Point simply being that clouds will have little impact at offseeting anything we get from other feedbacks which will be net positive

Canuck, one of the links I provided you (http://www.realclimate.org/index.php/archives/2006/07/runaway-tipping-points-of-no-return/) and the Pieerehumbert book goes over your question. In short, we cannot get a runaway greenhouse on Earth-- Chris

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Hi Chris. Your quote is fine until the end. The last sentence uses the word may without qualifying it with a probability. It also does not mention that the number of cyclones has decreased. The past decade has had fewer strong storms than the early part of the 1900s.

Climate is simply weather averaged over many years. The diurnal variation will not change. Your quote says that relative humidity is expected to remain constant. Since global warming therory suggests that the poles will warm more than the tropics, the earth's temperature would become more homogeneous. That would reduce surface temperature differences thus leading to fewer storms and weaker cold fronts.

As for the common situation of pressure preventing or allowing surface air to rise like I discussed, the temperature differential with respect to altitude is important. For coulds to get thinner as the earth warms, then the temperature difference between the surface and the upper atmosphere would have to decrease. How much thinner will they get? 10 percent? 20 percent? 80 percent? That will matter. Although since the upper atmosphere is cooling instead of warming contrary to global warming theory, the cloud thickness should actually increase.

Though people like Gore will disagree with you that there cannot be a runaway effect on earth, I was glad to read your last sentence.

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A lot of the problems expected from global warming have little to do with the pole-equator gradient and a lot of storms don't even result from that. I am still skeptical to linking increased cyclones with global warming, but it looks like over decadal scales we might see a trend in the future, but even the IPCC and other documents show there is less confidence in this area, but there are plenty of other problems associated with getting another 3 degrees C which I don't think people would disagree with me on (I guess you can disagree if we will get that 3 C) The upper atmosphere is expected to cool with increased greenhouse gases (Stratopshere and above) which is what we observe as http://www.climatescience.gov/Library/sap/sap1-1/finalreport/default.htm and the IPCC AR4 go over-- Chris

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Chris - my question was more rhetorical. Of course it's not possible for a runaway greenhouse effect on Earth. It was more focused towards a certain segment of GW supporters, who have raised the possibility of Earth turning into Venus, in hopes of scaring the great unwashed.
Glad to know you aren't part of that segment.

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"The upper atmosphere is expected to cool with increased greenhouse gases..." This is not correct. The theory suggests that the arid regions, the poles and upper atmosphere, will warm faster than other areas as the level of OCO rises in those areas. This is because they are arid, so water vapour is not competing with the new OCO molecules. That only one pole is warming and that they observe the cooling in the upper atmosphere indicates that there is something wrong with the theory -- or at least as it applies to the chaotic climate system.

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Originally Posted By: John M Reynolds
"The upper atmosphere is expected to cool with increased greenhouse gases..." This is not correct. The theory suggests that the arid regions, the poles and upper atmosphere, will warm faster than other areas as the level of OCO rises in those areas. This is because they are arid, so water vapour is not competing with the new OCO molecules. That only one pole is warming and that they observe the cooling in the upper atmosphere indicates that there is something wrong with the theory -- or at least as it applies to the chaotic climate system.


What do you mean by upper atmosphere? I was referring to above the tropopause (we've already been over upper vs lower troposphere as well), I'm not sure why you're bringing latitude into this. I'm not sure why I have to keep saying we aren't expecting antarctic warming over the entire region. I'd like to know where this checklist is that goes over what AGW says will and must happen, it must be on the internet somewhere, but...

old post

Quote:

Even still overall trends in Antarctica over the last century are toward a warming side with good certainty. Parts of Antarctica in the interior have cooled slightly, while other parts such as the Antarctic peninsula (where Larson B broke off) have warmed as you can see on the graphs:
http://data.giss.nasa.gov/gistemp/

However, dominant patterns controlling the atmospheric variability of the SH are the Southern Annular Mode (SAM) which is a shifting atmospheric climate pattern in the SH (which affects the westerly winds around Antarctica acting as a barrier to warmer air reaching antarctica) and the El Niño Southern Oscillation (ENSO) . See "Interpretation of Recent Southern Hemisphere Climate Change" from David W. J. Thompson Susan Solomon @ http://www.sciencemag.org/cgi/content/abstract/296/5569/895. For further info, the high-index polarity of the SAM favors geopotential height decreases throughout the polar cap (over the SH) and strong westerlies over the Southern Ocean. Thus, the high-index polarity of the SAM favors cooling over much of Antarctica. The positive phase of the SAM is associated with cold temps over parts of Antarctica (eastern Antarctica and the Antarctic plateau) and warm temps over the Antarctic Peninsula and Patagonia. Currently, a drift toward the positive phase is happening. A positive phase of the SAM is promoted by decreased ozone at the stratosphere and increased greenhouse gases at the troposphere, which is especially apparent over Antarctica. Gillett et al. (2006) found that the positive phase of the SAM is associated with significant cooling over Antarctica and some parts of Australia and also associated with warming over the Antarctic Peninsula, Argentina, Tasmania, and the south of New Zealand. Moreover, recent cooling trends have been associated with ENSO variability, See the paper from Bertler et al. (2004) @ http://www.agu.org/pubs/crossref/2004.../2004GL020749.shtml

Even more interesting stuff in Antarctica (as mentioned) is the role of ozone in the stratosphere. The N. P. Gillett, D. W. J. Thompson (2003) paper @ http://www.sciencemag.org/cgi/content/short/302/5643/273 and others demonstrates how the ozone hole in the Southern Hemisphere has affects Antarctic surface climate. This is why future projections for regional and global changes must account for ozone recovery, as (since the montreal protocol) the ozone has been in a more recovery period, and the problem now is the rapid increase in greenhouse gases. Another interesting paper in Science from Baldwin et al. also goes over this- http://www.sciencemag.org/cgi/content/summary/316/5831/1576 . Another point though, out of the benefits of ozone recovery, a negative is that it will promote warming over antarctica as described here: http://www.nasa.gov/home/hqnews/2004/oct/HQ_04337_antarctic_change.html (since the decreased ozone promotes a positive SAM which promotes a cooling, the reverse effect {of increased} ozone will initiate opposite effects).

An interesting side note is that the stratosphere cooling with troposphere warming is strong evidence for a CO2 warmed climate without a primary influence from natural variability.

Regarding the accumulation of ice in Eastern Antarctica, this is most likely the result of warmer oceans with an increase in evaporation and precipitation (a warmer climate holds more water vapour) over a region of Earth that is usually very cold, and since Antarctica is a desert, precipitation rates are extremely low. An article in Science by Davis et al. (2005) states that data from satellite radar altimetry indicates that the East Antarctic ice-sheet interior increased in mass by 45 [+ or -] 7 billion metric tons per year from 1992 to 2003 due to increased However, to my understanding, the total mass of both the Arctic and Antarctic Ice Sheets are in decline.
http://www.eurekalert.org/pub_releases/2006-03/uoca-ais022806.php

West Antarctica and other parts are a different story: This piece of the Larsen B Ice Shelf broke off rapidly in March 2002. The piece was roughly as large as the state of Rhode Island:


NASA and University of Colorado researchers found that the break up of the Larsen B ice shelf in 2002 led to a significant acceleration of West Antarctic glaciers flowing into the Weddell Sea. In West Antarctica researchers also found that glaciers flowing into the Amundsen Sea are speeding up considerably during the last decade. Right now, looks like West Antarctic glaciers is accelerating sea level rise. Three papers you should look at concerning this:

http://www.sciencemag.org/cgi/content/abstract/315/5818/1529

http://www.sciencemag.org/cgi/content/ab...ourcetype=HWCIT

http://www.agu.org/pubs/crossref/2004.../2004GL020697.shtml

In the longer term, we do expect Antarctica to end up warming, but nothing going on right now contradicts AGW. SAM and ENSO have had major effects on the area, as the AR4 also goes over. The ozone hole has strentherned a positive phase of SAM and right now we expect these certain areas to cool. However, global temperatures continue to rise, and we know the arctic warms much faster than Antarctica which is observed.

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"What do you mean by upper atmosphere?" Stratosphere where the temp is around -50 C.

"I was referring to above the tropopause (we've already been over upper vs lower troposphere as well), I'm not sure why you're bringing latitude into this."

I am not sure if that is supposed to be two separate topics, but since it is a single sentence, I will treat it as one. I brought up both altitude and latitude. They are both arid places that should be affected more by increases in OCO due to the lack of competition from water vapour. That is what was being pushed around 2003 and 2004 because of the increased 2002 and 2003 calving in the Antarctic Peninsula. The amount of calving has decreased since then. Your quote also brought up ozone. Ozone is a green house gas. It is least plentiful in the winter. That ozone is slowly increasing in concentration should allow Antarctica to warm even faster. That Ozone holes still exist in the cold, increasing levels OCO should still be even more important in the winter.

Here is an article from 15 January 2002:
Quote:
Antarctica overall has cooled measurably during the last 35 years - despite a global average increase in air temperature of 0.06 degrees Celsius during the 20th century - making it unique among the Earth's continental landmasses, according to a paper published today in the online version of Nature.

http://www.scienceagogo.com/news/20020015034521data_trunc_sys.shtml

The lead author of that study does not like how the media, and people like me, interpret his work.
http://tigger.uic.edu/~pdoran/antarctic_cooling.html
He says, "...we indeed stated that a majority -- 58 percent -- of the continent cooled between 1966 and 2000, but let&#8217;s not forget the remainder was warming."

According to AGW theory, cold arid regions are supposed to be affected more than warm humid areas like the tropics. That 58% of Antarctica was able to cool is the entire point. That goes against the whole OCO green house gas forcing theory.

He said, "One region, the Antarctic Peninsula, warmed at orders of magnitude more than the global average." That is what was supposed to happen. That it did not apply to the entire continent, and that the trend has been toward cooling for 58% of the continent is significant.

By the way, your first link does not mention Antarctica and you second link does not work.

Did you even read the last 3 links of yours about the 2002-2003 year? They are off topic. The rest of your post looks at only the 1992-2002 decade. As the http://www-das.uwyo.edu/~geerts/cwx/notes/chap03/antarctica.html link's last (Standard deviation) graph shows, there seems to be a loose correlation between the Southern Oscillation Index and the south pole temperature. That seems to be all we ever get -- loose correlations.

Here is another link to a page titled, "Antarctic Temperatures of the Past Two Centuries" http://ff.org/centers/csspp/library/co2weekly/20061013/20061013_02.html This shows how the 1820s, 1930s, and 1990s saw a warm Antarctica.

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Remove the period from link 2, and link 1 can be whtever you want, play around with it. It is well known that Antarctica is not just being affected by GHGs and more precipitation but ENSO, SAM, and Ozone depletion. There is an abundance of literture on this. I don't see wht you're arguing, and I don't think you know what you are either.

"That goes against the whole OCO green house gas forcing theory." not really

Please go over the thousands of pages of resources available on the internet, or take time to contact experts on the subject.-- Chris


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