Some comments on AGW
Posted by Jeff Id on October 23, 2009
My computer has a virus so I can’t do much of anything. Sorry for not interacting much on the threads. I’m working on repair and will probably be back up tomorrow. In the meantime Dr. Weinstein has a few thoughts on conclusions in AGW he wanted to share.
Leonard Weinstein, ScD
October 23, 2009
The “Positive Feedback” issue:
A write-up at http://chriscolose.wordpress.com/2009/10/08/re-visiting-cff/ reviews the climate forcing/feedback concepts. The basic review of the direct effect of CO2 seems very reasonable, and concludes that a doubling of CO2 would give a temperature rise of about 10C if there were no feedback. The write-up then states that best evidence, as stated in the IPCC 2007 report, indicated that the actual effect would be 20C to 4.50C per doubling of CO2 rather than 10C, due to positive feedback effects. The paper then shows a figure with several model calculations of possible contributions from all expected main sources of the feedback. All of the expected terms except water vapor are relative small and may even result in a slightly negative feedback. However, the contribution due to expected increased absolute water vapor content at higher altitudes is calculated to give a feedback multiplier about 2, and is by far the dominate term in the expected feedback. However, the absolute water vapor content as a function of altitude and date has been measured, and is shown in http://junkscience.com/Greenhouse/moisture.html. The data, which was obtained from ESRL, is shown for near ground level to 30,000 ft altitude. It should be pointed out that the higher altitudes are where the feedback is supposed to occur. The only conclusion seen for data from 1948 to 2008 is that the absolute level is slightly dropping except very near the ground. This is the opposite of what is needed for positive feedback, and in fact shows that a slight negative feedback should exist for that time period due to water vapor.
Residence time of CO2:
The monthly CO2 readings obtained at Mauna Loa (http://www.esrl.noaa.gov/gmd/ccgg/trends/) and other sites vary in a yearly cycle, which is superimposed on a continual rising average. The maximum drop rate within the cycles occurs in the northern hemisphere fall season. The average maximum drop rate is about 2.3 ppm per month at a level of about 386 ppm. This implies a maximum drop rate time constant of 168 months or 14 years. However, natural and continually increasing anthropogenic CO2 production did not stop during that time. The probable cause of the drop is the greater solubility of CO2 in cooling water due to dropping temperatures. A similar maximum rise rate of CO2 is found in spring as northern oceans warm. Since the majority of land and human activity are in the northern hemisphere, the unbalanced global land and activity location may cause the change since atmospheric mixing with the southern hemisphere has a lag time of at least several months to over a year. If the total anthropogenic emitted level were to totally stop, the ocean absorption time constant would almost surely be even shorter due to the larger drop. Since the upper layer of the ocean mixes well to a depth of several hundred feet within a few weeks, and the northern latitudes portion of this surface layer (the part that dissolves the most CO2) is in fact removed to a large depth by the surface and thermohaline currents within a few months, the excess trapped surface CO2 would thus be removed in a time constant even shorter than the ocean absorption time constant. This indicated that the residence time of CO2 in the atmosphere is almost surely much shorter than 100 years as claimed by AGW supporters. A probable mechanism for the fairly rapid removal of CO2 from the atmosphere would be by dissolving in raindrops, which then drop into the oceans. One time constant drop of CO2 would lower the excess atmospheric level by over 60%, and each additional time constant would drop it over 60% of the remainder. The literature is full of references that indicate the atmospheric residence time constant for CO2 is close to 10 years, which is in reasonable agreement with this observed variation. The question arises, where do CAGW supporters get a value of 100 years?
Local vs. average temperatures:
Using worldwide temperature averages as a function of time may miss an important fact. Since the timing of the relative peaks and dips in regional temperatures are at least somewhat random in when they appear, they sometimes overlap and sometimes are out of phase, This results in variations of the average global temperature but this is not necessarily due to drivers such as Solar variations, or changes in CO2 levels. It is more likely that it is a combination of long period ocean current lag and natural chaotic effects that occur in such a complex nonlinear system. For example, the Sargasso Sea, Greenland, and Antarctic temperature variations (and many other regional areas) all occurred with similar rates and maximum amplitude of variation over all reasonably long-term time scales. However, the peaks and dips of the three regions mentioned did not always exactly line up. However, the overlap corresponding to the Medieval Climate Optimum is at least northern hemisphere wide, and seems to have occurred even in parts of the southern hemisphere also. The Little Ice Age and recent warming appear to be very much worldwide events. Claims that the poles heat (and cool) faster than the rest of the world average may be true, but so do many other regions. It may only imply that a selected but limited size region is more correlated in change than the sum of regions over the entire Earth. Europe and Northern US both had unusual large temperature swings in the not too distant past that lasted several years to decades, but they sometimes occurred at slightly different times. If the amplitude of the swings at the poles loses their unique speed of change feature, this minimizes the impact of another common assumption that something has to be causing the global warming. It is reasonable that if a forcing such as a large Solar effect or large CO2 change occurred, the poles would heat faster than typical other locations, but this does not seem to be the present case. In fact the Arctic heated about as fast and reached similar peak values in 1912 to 1942 as 1972 to 2002 (it doesn’t matter which was slightly larger, they were close). The earlier period is not thought to be anything but natural variation. The Antarctic has heated only a small amount over the time it has been monitored, and recent decades may even have net cooling, or at most small net warming.
The hypothesis for an anthropogenic caused temperature rise of 20C to 60C by 2100 and more rise beyond that time is running out of any positive arguments. I would like to see any falsifiable claims that support that hypothesis, and that can be examined in a reasonable time period.