Back-Checking the Hockey Stick

(H/T the Talkmaster)

Take a look at the following graph and see if you can tell what it is and what it means:

If you couldn’t tell the above graph, linked from Climate Audit, is the now famous “Hockey Stick” graph that depicts global temperatures over the last roughly 2,500 years. The data comes from tree-ring data, which is considered by climatologists to be among the more accurate methods of determining global mean temperatures before thermometric data (observed temperatures using thermometers) was available.

As you can see, there are two lines, one red and one black. The red line of the graph shows a tremendous spike toward the right hand side, depicting global temperatures rising precipitously during the last roughly 150 years. This is the Hockey Stick: Relatively stable rising and falling of temperatures over 2,300 years, then sudden rise over the final 200. This chart was depicted in 1998 by Dr. Michael Mann, a US-based climatologist. The IPCC, various governments and evironmentalists use Mann’s report, among others, and his graph to back up their claims that human beings are causing global warming an CO₂ emissions are the culprit.

After its release, Steve McIntyre, a Canadian statistician, saw the graph and believed it to be flawed. It seemed to eliminate the so-called “Medieval Warm Period,” the period from 900 CE to 1300 CE, when temperatures were much warmer than they were during the preceding 400-year-long “Dark Ages” or the following 450 years, a period known as the “Little Ice Age.”

Filed under: environment, politics, agw, briffa, climate, climate change, climategate, climatology, cru, dark ages, environment, global warming, hockey stick, ipcc, little ice age, mann, mcintyre, medieval warm period, politics, roman climate optimum