Global warming isn't just hot air

Robert Wilson says, "It is true that CO2 levels have risen some 18 to 20 per cent over the past 100 years. But average global temperatures have emphatically not. This statement cannot be supported by well-known data."

Wilson seems to be attacking a straw man here. Who is claiming that average global temperatures have risen 18 to 20 per cent in the last century? Not the IPCC, not NASA.

Wilson says that, "Over the past 100 years, we have had two distinct warming periods (1900-1940 and 1980-2003)" and "one cooling period (1950-1975)." The IPCC also states that there have been two warming periods and an intervening cooling period, but that the later period has not ended.

Frequently Asked Question 3.1, derived from the AR4 report by IPCC Working Group 1: The Physical Science Basis of Climate Change (http://ipcc-wg1.ucar.edu/wg1/FAQ/wg1_faq-3.1.html) notes that "Warming in the last century has occurred in two phases, from the 1910s to the 1940s (0.35°C), and more strongly from the 1970s to the present (0.55°C). An increasing rate of warming has taken place over the last 25 years, and 11 of the 12 warmest years on record have occurred in the past 12 years [(1995 to 2006)]." There was "a slight cooling (0.1°C)" between the 1940s and 1970s.

Wilson states, "Now it is becoming very clear within the past few years that another cooling period has just begun." Yet the NASA webpage Global Temperature Trends: 2007 Summation states, "The year 2007 tied for second warmest... behind the record warmth of 2005," and adds, "It is apparent that there is no letup in the steep global warming trend of the past 30 years."

Wilson states, "According to the latest information from NASA, the warmest year of the 20th century was way back in 1937." Wilson is likely referring to a "minor data processing error" that led NASA to re-evaluate its global temperature data (see the NASA 2007 Summation webpage cited previously).

Unfortunately, Wilson's statement is problematic in several respects. First, the year in question is 1934, not 1937. Also, NASA states the years 1934, 1998 and 2005 are in a "statistical tie" as "the warmest year(s)" in the contiguous United States, as can be seen in Figure 4b ("U.S. Temperature") on the same webpage.

Figure 4a ("Global Temperature") next to it shows global temperatures since the 1980s as warmer than the warmest temperatures from the 1910s to 1940s warming phase, and climbing steadily.

Wilson states, "As reported by the Associated Press, seven northern California glaciers are now advancing, and in fact nearly half of glaciers worldwide are now advancing--not retreating."

Here is a quote from the AP article that Wilson cites: "Global warming is shrinking glaciers all over the world, but the seven tongues of ice creeping down Mount Shasta's flanks [in California] are a rare exception: they are the only long-established glaciers in the lower 48 states that are growing." Mount Shasta's glaciers are growing due to "changing weather patterns over the Pacific Ocean" it adds, i.e., climate change.

Wilson encourages people to search for the "truth" about global warming. I would very much encourage Courier readers to do as I did upon reading his letter, which is to check it for accuracy. Visit the NASA website, go to www.realclimate.org (a website about climate science by climate scientists), and review the contents of Wilson's letter and my letter for yourselves.