The famous Hockey Stick chart shows a general decline in estimated temperatures of about 0.4C from 1000 A.D. to 1900, followed by a rise of about 0.6 that begins about 100 years ago. Whether or not this impression was intended depends upon your feelings about nuances of speech. The temperatures clearly began their rise 100 years ago, in a fashion that graphs pretty much like a straight line. All witnesses mentioned climate model forecasts for the future. The pivotal point that somehow eluded our elected officials is that accepting the Hockey Stick temperature history in fact militates against the overall urgency of the global warming issue.
Every climate model predicts that human warming is greater in winter than in summer.
In his testimony, Christy alluded to the likelihood of that being a net positive influence. That omission may be because the data sources used for the Hockey Stick, such as tree rings and corals, are far from perfect annual and global thermometers. Corals grow mainly in tropical oceans, where climate fluctuations are probably small compared with global changes. It then becomes incumbent upon scientists to demonstrate that global warming increases the likelihood of greater regional temperature variability. Temperature variability has been declining for 50 years.