It is a tenet of catastrophic anthropogenic global warming theory (CAGW) that our carbon dioxide emissions are the major cause of recent global warming. Although carbon dioxide is a very weak greenhouse gas, CAGW theory holds that it is enough to start the warming process which, in turn, evaporates water, and water vapor is a very strong greenhouse gas. CAGW proponents ignore the fact that more water vapor in the air produces clouds which block the sun (more on that below).
It follows from CAGW doctrine that more carbon dioxide emissions should increase the humidity of the air, thus establishing an enhanced greenhouse effect. Is that happening?
A new paper, Trends in U.S. surface humidity, 1930 – 2010, Journal of Applied Meteorology and Climatology, finds just the opposite: “Average long-term trends (1930 – 2010) indicate that temperature has warmed, but little change has occurred in dewpoint and specific humidity.” In other words, the mechanism for CAGW’s enhanced greenhouse effect is not happening according to observational data.
How, then, do we account for warming in the 20th Century? Back in 2005, Dr. Roy Spencer published a book: “The Great Global Warming Blunder: How Mother Nature Fooled the World’s Top Climate Scientists” (see my review here). In that book Spencer proposed that “The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling.” Could such a small change in cloud cover be significant?
A new paper just published in the Journal of Climate finds that global cloudiness has decreased over the past 39 years from between 0.9 to 2.8% by continent. See graphs and a discussion of the paper at WUWT here.
The first paper falsifies the major CAGW tenet; carbon dioxide has been increasing but there has been no increase in humidity. The second paper provides confirmation of a natural control of global temperatures.
For a more detailed discussion of climate sensitivity to carbon dioxide see here. “Examination of Earth’s climate sensitivity by varied derivation reveals climate to be remarkably insensitive to changes in forcing from enhanced greenhouse effect.” “Evaluation of Earth’s natural greenhouse effect reveals forcing response to be considerably less than line by line spectral radiance evaluation would suggest. Net feedbacks are found to be negative.”