Chris
Breaking the record into the apparent 30-year cycles (as Girma has done) there is the 30-year warming cycle from ~1911 to ~1940 (which was “statistically indistinguishable” from the latest 30-year warming cycle from ~1971 to ~2000, according to Phil Jones), followed by the 30-year cycle of slight cooling from ~1941 to ~1970 (which occurred despite the fact that CO2 emissions were beginning to accelerate as a result of the post-WWII boom years).
http://www.woodfortrees.org/plot/hadcrut3vgl/from:1941/to:1970/plot/hadcrut3vgl/from:1941/to:1970/trend/plot/hadcrut3vgl/from:1911/to:1940/plot/hadcrut3vgl/from:1911/to:1940/trend/plot/hadcrut3vgl/from:1971/to:2000/plot/hadcrut3vgl/from:1971/to:2000/trend/plot/hadcrut3vgl/from:2001/to:2011/plot/hadcrut3vgl/from:2001/to:2011/trend
The warming/cooling cycles are underlaid by a slight warming trend of around 0.5 to 0.6°C per century, like a sine curve on a tilted axis.
It is quite apparent that these cycles, as well as the latest 11 years (starting in 2001 (which again shows slight cooling), bear little correlation with the steadily increasing CO2 levels.
This is Girma’s point, and it is pretty hard to invalidate based on empirical evidence, as you will have to admit.
One can deny that the cycles exist, but that would simply be sticking ones head in the sand in denial.
The unanswered question remains: will the current trend of slight cooling continue for another 19 years or so to become another 30-year cooling cycle, or will it reverse to a new warming cycle?
No one knows the answer to that question.
Certainly not the scientists and climate models cited in IPCC AR4, who had projected that it would warm by 0.2°C per decade instead of cooling slightly, as it actually did.
The second question (also unanswered) is: what has caused these observed ~30-year warming and cooling cycles?
And finally, the third question could be: what has caused the underlying long-term warming trend of around 0.6°C per century?
Max