On September 1, a report released in the Proceedings of the National Academy of Sciences confirmed the 1998 "hockey stick" graph showing a trend of rising global temperatures. The graph indicated that the temperatures of the Northern Hemisphere remained relatively constant for 1000 years (the "shaft" of the stick) and suddenly rose with the advent of the industrial revolution. Multiple data analysis tools were used to support the conclusion.
"We used two different methods that are quite complementary in the assumptions they make about data, so that provides a test of the sensitivity of data to the methods used," said climate scientist, Dr. Michael Mann of Pennsylvania State University. "The science is not all done, there's still a lot of work to do; but what we are seeing now is definitely unusual in the context of the past."
The scientists also found that surface temperatures in the Northern Hemisphere were warmer over the last 10 years than any time during the last 1,300 years, and if scientists include controversial data obtained from tree rings, the data shows the warming is anomalous for at least 1,700 years. "Ten years ago, we could not simply eliminate all the tree-ring data from our network because we did not have enough other proxy climate records to piece together a reliable global record," said Mann. "With the considerably expanded networks of data now available, we can indeed obtain a reliable long-term record without using tree rings."