It is the other two parts of the theory where the Warmists and the Skeptics part company. The second part of the theory has to do with feedback. The release of CO2 alone is not enough to cause the major problems predicted by the global warming advocates. The theory calls for the increase in warming due to CO2 to cause more evaporation of water which increases the water vapor in the atmosphere. Water is the major greenhouse gas so it will magnify the greenhouse effect.
Warmists see the increased water vapor providing positive feedback to global warming. The added water vapor according to them will break up low level clouds and create high level cirrus clouds which add to global warming. These Cirrus clouds will also cause a so called “hot spot” in the troposphere as more heat is captured higher up in the atmosphere.
Skeptics also see CO2 as increasing water vapor, but they see this water vapor acting as a negative feedback. Rather than break up low level clouds, skeptics see the water vapor adding to the low, thick clouds (such as stratocumulus) which primarily reflect incoming solar radiation back into space. This would negate the formation of a hot spot and cool the planet. In addition, these low level clouds will cause rain to fall which also acts as a cooling mechanism to the planet.
In Spencer et al. (2007) found a strong negative cirrus cloud feedback mechanism in the tropical troposphere. Instead of steadily building up as the tropical oceans warm, cirrus cloud cover suddenly contracts, allowing more OLR to escape. Dr. Roy Spencer of the University of Alabama in Huntsville, who directed the study, estimates that if this mechanism operates on decadal time scales, it would reduce model estimates of global warming by 75%.
The science regarding clouds is not well understood. We simply don't know exactly what will happen with additional water vapor in the atmosphere, but the affect could be significant. A 1 percent change in clouds could account for all of the shifts in climate over the past 2000 years.
Now there are two checks to see which theory (positive or negative feedback due to increased water vapor) is correct. The first is to see if the predicted hot spot can be found.
Douglass et al. (2007) compared model-projected and observed warming patterns in the tropical troposphere. The observed pattern is based on three compilations of surface temperature records, four balloon-based records of the surface and lower troposphere, and three satellite-based records of various atmospheric layers–10 independent datasets in all.
“While all greenhouse models show an increasing warming trend with altitude, peaking around 10 km at roughly two times the surface value,” observes the NIPCC, “the temperature data from balloons give the opposite result; no increasing warming, but rather a slight cooling with altitude”
So there is no hot spot even though the IPCC says there should be one. As you can see from the figure above, all the models call for increasing temperature peaking approximately six miles up, while there is no observation confirming this.
The only argument I’ve seen from the Warmists on this missing hot spot is one paper which concluded to measure the temperature at altitude as they must, you shouldn’t use thermometers but rather measure wind speed and infer from the wind speed an increase in temperature. If you do this, you can infer a hot spot.
The second “proof” would be to look at the radiation budget. If water vapor is a positive feedback, it would show up as a decrease in the amount of radiation being reflected back into space. This is in fact what all 11 IPCC models show while the actual data from ERBE (purple below) is just the opposite.
In a study done by Lindzen he found with the warming after 1989, the observations characteristically exceed 7 times the model values. If the observations were only 2-3 times what the models produce, it would correspond to no feedback. What we see is much more than this – implying strong negative feedback. Note that the ups and downs of both the observations and the model (forced by observed sea surface temperature) follow the ups and downs of temperature. Alarming climate predictions depend critically on the fact that models have large positive feedbacks. The crucial question is whether nature actually behaves this way? The answer is unambiguously no.
You can read about it here http://wattsupwiththat.com/2009/03/30/lindzen-on-negative-climate-feedback/
Skeptics look at the water vapor feedback portion of the AGW theory and see that it falls apart. The feedback apparently is negative feedback, not the positive feedback used in the global climate models.
The "So What" Factor
The next area of the AGW theory is the Paleoclimatology portion. This was the portion that is used to raise the alarm. If the globe was warming, but it had done so before with no serious consequences, the basic response to the alarmists would be “so what?”
Michael Mann is the main character in this drama with M&M (McIntyre and McKitrick) being another important group. Back in the late 1990s, the global warming cabal was gaining ground. For 10 years (today that is not enough to establish anything—it’s just weather) the temperatures had been going up. There was a dedicated group of scientist who saw this as proof of human caused global warming. They had the first two legs of the global warming theory, but were running into the “so what” factor. In fact, when they raised the alarm a great many skeptics not only said “so what,” but pointed out that during previous warm periods in the Roman times and the Medieval times this warming was a boon to humans.
In steps Michael Mann. In 1998 he published his report MBH98 in which he showed a history of relatively flat temperatures to 1900 followed by a sharp increase. The term hockey stick was coined by the head of the NOAA’s Geophysical Fluid Dynamics Laborarty Jerry Mahlman.
A series of investigations were done. Mann has claimed vindication, but the truth seems to be something else. Mann cites as evidence of this that his ‘hockey stick’ study was:
Almost immediately there was a lot of controversy about this study. Using bristlecone pines as his proxy, Mann indicated that these were excellent proxy indicators of temperature, and due to their age, a profound record of temperature. But other sources indicate this is not the case.
In a NOVA article were these passages:
"It turns out that the bristlecone pine has evolved survival strategies that might make other, less hardy plants, well, green with envy. These strategies help it cope with one of the most flora-unfriendly environments."
Nowhere in the NOVA article does it link temperature and tree ring growth for Bristlecone pines, but it seems clear that water is a major factor in BCP growth.
Next came M&M. You can read about them here: http://frontpagemag.com/2010/02/19/the-heretics-mcintyre-and-mckitrick/
These two scientist started a crusade to get the data so they could check Mann’s work. For over 10 years Mann refused to allow them to see his data, but they still managed to look at his mathematics. Their criticisms were that Mann et al.'s reconstructed millennial temperature graph (the hockey stick) was an artifact of flawed calculations and serious data defects; in turn, MBH replied that these criticisms were spurious. M&M found the mathematics Mann used would produce a hockey stick even if you put random numbers in.
vindicated in a report by the U.S. National Academy of Sciences and seeks to back up this assertion by citing the way the media reported this study as ‘Science Panel Backs Study on Warming Climate’ (New York Times), ‘Backing for Hockey Stick Graph’ (BBC), and so on.
This is, to put it mildly, disingenuous. NAS actually agreed with the McIntyre/McKitrick criticisms. Far from vindicating the ‘hockey stick’ graph, the NAS said that although it found some of Mann’s work ‘plausible’, there were so many scientific uncertainties attached to it that it did not have great confidence in it. Thus it said that:
“uncertainties of the published reconstructions...Even less confidence can be placed in the original conclusions by Mann et al. (1999) that ‘the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium.’
What Mann also does not say is that a subsequent House Energy and Commerce Committee report chaired by Edward Wegman totally eviserated the credibility of the ‘hockey stick’ study and devastatingly ripped apart Mann’s methodology as ‘bad mathematics’. Furthermore, when Gerald North, the chairman of the NAS panel -- which Mann claims ‘vindicated him’ – and panel member Peter Bloomfield were asked at the House Committee hearings whether or not they agreed with Wegman’s harsh criticisms, they said they did:
CHAIRMAN BARTON. “Dr. North, do you dispute the conclusions or the methodology of Dr. Wegman’s report?”DR. NORTH. “No, we don’t. We don’t disagree with their criticism. In fact, pretty much the same thing is said in our report."
DR. BLOOMFIELD. "Our committee reviewed the methodology used by Dr. Mann and his co-workers and we felt that some of the choices they made were inappropriate. We had much the same misgivings about his work that was documented at much greater length by Dr. Wegman.”
WALLACE:”‘the two reports were complementary, and to the extent that they overlapped, the conclusions were quite consistent.’ (Am Stat Assoc.) in our report”
There is a huge amount of writings on the hockey stick. Some ardent warmist defend it even today. But I agree with many skeptics who call the hockey stick the MOST discredited study in history.
Tomorrow Climategate explained