[whd23]

The original idea—conceived by Penn State's Mann while still a postdoctoral researcher—was to surmise temperatures, going back 1,000 years, from such data as the thickness of the rings of bristlecone pine trees, which grow faster in warm summers than in cool ones. The method, for technical reasons, didn't work for the last two decades of the 20th century.

Uh, I call baloney on this. If tree-ring growth measurements don't correlate to temperature for the last two decades of the 20th century then they don't for any other period of time. There can be no rational "technical reason" why they should no longer correlate; trees didn't evolve a new growth pattern in 1980.

[ModelBreaker]

“There can be no rational “technical reason” why they should no longer correlate; trees didn’t evolve a new growth pattern in 1980. “

I’m sure global warming is to blame for it. In fact, the lack of correlation probably proves CO2 global warming.