Reexamining The Anthropogenic Global Warming Issue
Posted by Jeff Id on December 27, 2009
Leonard Weinstein, ScD
The following is an effort to reduce the AGW issue to a minimum number of necessary claims to support or reject. When I read of “thousands of supporting papers” on the issue, I would like to hear what these papers show that refutes the following.
The issue of anthropogenic global warming and its consequence arose from several factors. The obvious three main factors that prompted the issue coming up were:
The global average temperature has been rising noticeably since about 1850 (with obvious results of glaciers melting, sea level rising, etc)
The atmospheric CO2 concentration has been increasing significantly since it was first accurately measured in 1958, and proxies indicate the main part of the rise started about 1850. This rise seems to be clearly related to human burning of fossil fuels.
There is a theoretical basis for the fact that CO2 is a major greenhouse gas and contributes to the surface temperature level.
It seemed an obvious step to correlate the temperature rise to the human activity. The next step that followed was an effort to estimate the long-term effect of continuing increases in the use of fossil fuels, and thus production of CO2. This was particularly important, since the developing nations of the world seemed headed to ever-greater uses of fossil fuels as their economies expanded.
The theoretical models only show a modest temperature increase from the direct effect of the increase of the CO2. Additional factors had to be implicated before the increase could be considered a problem. Some studies indicated that there was a feedback effect from increases in CO2 level that greatly magnified the resulting temperature increase. The mechanism was that the modest temperature increase from the increased CO2 also caused the water vapor content of the atmosphere to increase. Water vapor is the primary greenhouse gas and has the largest contribution to the Earths surface temperature increase. The increase in water vapor engendered by the increased CO2 then causes more temperature increase, and this results in a net positive feedback. The estimate generally used (but not proven) is that there is a gain of a factor of 3X over the direct CO2 effect alone. With the large positive feedback assumption and projected increase in CO2 from growing worldwide fossil fuel burning activity, computer models were developed to estimate the worldwide increase in temperature over the next several decades. These models all showed significant increase in temperature over the next 50 to 100 years and longer, and raised considerable concern.
In order for the models to be reasonable, two facts had to be established:
Much of the temperature rise since 1850 had to be shown to be not due to natural variability, but due to human activity, with the greatest activity from 1970 to the present.
The positive feedback with large gain factor due to water vapor had to be supported by measured data.
The first of these two facts required that the global temperature rise since 1850, with emphasis from 1970 to the present, had to be significantly larger and occurring faster than any other time in at least the last couple of thousand years, so that it would not be reasonable to associate the recent rise with natural variability. This requirement seemed to contradict the previous best understanding of the global temperature variation. Previous work had indicated that there were periods of warming and cooling every few hundred to thousand years that were comparable to the recent one. However, since the direct temperature measurements only went back a few hundred years, and direct global measurements even a shorter time, the older global variation had to be determined by indirect measurements from proxies.
There are several proxies that can be used. These include ice cores from glaciers, cores from sea floors, coral cores, tree ring data, bore hole temperature distributions, etc. All of the proxies are limited in the number of locations they can be obtained from, or in temporal resolution, and many have sensitivity to several parameters. As an example, tree ring data is affected by cloudiness, rainfall, CO2 fertilizer, and surrounding conditions as well as temperature, and in fact does not measure nighttime or winter temperature, so extracting just average temperature data is not easy and in fact may be not possible in many cases.
Some data that was deduced from these proxies seemed to support the claim that even though some regions (such as Europe and Greenland) may have had other warm periods such as the “Medieval Warm Period” and cooling periods such as the “Little Ice Age”, that these were regional and not world wide as the present warm period is. If that was true, then the present period of worldwide warming would seem to be unique over the last several thousand years.
However, more recent and complete data, along with reanalysis of some of the previous data, contradicts that conclusion of uniqueness of the present average temperature. In addition, the present temperature trend is not continuing upwards even though CO2 is still increasing. The comparison of the present temperature trend to previous trends falsifies the claim of uniqueness of the temperature rise. The upper Troposphere absolute water vapor content has not increased with increasing CO2, and the temperature trend has continued flat or even down for the last few years. This tends to falsify the positive feedback assumption between CO2 and water vapor. In addition, the present low sunspot activity and PDO phase make it very likely that there will be more cooling over the next several years. With these two claims falsified, there is NO argument supporting AGW, and the computer models are clearly GIGO.