A graph depicting the variations in and rise of the Earth's surface temperature over the past 1000 years; aka the "hockey stick" graph. Image source: Third Assessment Report of The Intergovernmental Panel on Climate Change, Chapter 2, Figure 2.20. The source of this image is <a href="http://www.grida.no/climate/ipcc_tar/wg1/pdf/WG1_TAR-FRONT.PDF">this PDF file</a>.
Picture a hockey stick lying on its side, the shaft to the left, the blade rising sharply on the right. The left side stretches back about a thousand years, the right side shows the recent past.
That’s the “hockey stick” reference coined by climatologist Jerry Mahlman, following the 2001 United Nations Intergovernmental Panel on Climate Change, to describe the sharp upturn of the earth’s temperature in the 20th century – in other words, global warming.
Since then, the Hockey Stick symbol has been the central icon of the battle over climate change within the scientific and political communities – who often find themselves in polar opposition over the topic. In his new book, Nobel Peace Prize-winner Michael E. Mann, lead author on the scientific paper that introduced the infamous symbol, explores the controversy and unravels the political and market influences behind the denial of what, he believes, is irrefutable scientific fact.
Mann, who became an accidental and reluctant public figure in the debate on this issue, says that the image became iconic because it's a simple, yet powerful illustration of the otherwise obscure data about global warming.
"It's a simple graph and it tells a simple story," said Mann. "What it shows is that the recent warming, the warming of the past century which is what you might think of as the blade of a hockey stick exceeds the warmth that we estimate as far back as we were able to go, at least 1000 years ago. You didn't need to understand the math and physics behind a theoretical climate model."
Has worldwide human activity brought on by the industrial age led to raised CO2 levels, the proliferation of greenhouse gas, melting ice floes and the threat of extinction?
Or is the Hockey Stick theory a hoax, a cause célèbre held up by environmental extremists to support government regulations on the oil and energy industries?
Can the scientific community ever find middle ground? Is global warming for real? If so, can it be reversed?
Michael E. Mann, professor, meteorology, Penn State University; director, Penn State Earth System Science Center; author, “The Hockey Stick and the Climate Wars: Dispatches from the Front Lines”