Yesterday’s Washington Post ran a letter from the Central Valley (CA) program manager for a National Parks Conservation Association, titled “How to counter climate change”. The writer informs us that “climate change is melting snow packs and mountain glaciers that communities such as the Central Valley in California depend on for irrigation, drinking water and power generation”, to stop which “the federal government must cut pollution from coal-fired power plants”.
That, of course, is the same Central Valley where the daytime temperatures have been falling but whose nighttime temperatures have been warming rapidly, as Christy et al revealed (pdf pp. 13-18) are indeed directly a result of Man, but the agriculture-intensive Valley’s own land-use/irrigation.
Here is the point: when you look at daytime temperatures of the Valley versus the Sierras, you see a dramatic drop in the temperatures in the Valley versus the Sierras in the daytime, especially during the summer, and that is what is consistent with irrigation. Irrigation will cool the air in the boundary layer. You won’t see this up in the deep layer of the atmosphere, but in the boundary layer you would. Now in the nighttime temperatures, you see here rapid warming in the Valley; relative to the mountains, it peaks in the irrigation season. This is consistent with two things, both irrigation and urbanization. But what you don’t see up there is something that is consistent forcing of that particular part of the world. [pdf p. 14]
[Abstract of full paper: Christy, J. R., W. B. Norris, K. Redmond, and K. P. Gallo. 2006. “Methodology and Results of Calculating Central California Surface Temperature Trends: Evidence of Human-Induced Climate Change?” Journal of Climate 19(4): 548—563].