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Mondays, 4:35 - 5:35 p.m.

Lectures in L1175
Labs in L1110

Introduction Instructors

In 1998, a seminal study by Mann, Bradley and Hughes took advantage of climate signals embedded in an array of high-resolution paleoclimate proxy data to conclude that "Northern Hemisphere mean annual temperatures for three of the past eight years are warmer than any other year since (at least) AD 1400." The so-called "hockey stick" reconstruction showed relatively stable temperatures for most of the millennium, until the start of the Industrial Revolution, when reconstructed temperatures begin a rise to a level not seen in the last millennium (see Figure above).

Since 2001, when the third assessment report by the IPCC featured the "hockey stick" prominently, this graph has become the emblem of the debate on anthropogenic global warming and the target of numerous attacks by global warming skeptics. No other picture conveys how anomalous recent climate change is in the context of natural variations in temperature over the past millennium. Defended as definitive proof of global warming by most climate scientists, hailed as a "misguided and illegitimate investigation" by skeptics, it remains one of the most hotly debated climate studies ever published. In the last two years, climate skeptics have joined forces with some powerful Republican lawmakers in a well-engineered effort to discredit the Mann et al. reconstructions, and in doing so cast reasonable doubt on all aspects of climate change research.

How was the "hockey stick" constructed? Based on what data, and using what methods? What conclusions can we draw from it? Were the criticisms justified? What has been made in the past 9 years to address them, and do the conclusions still stand? And perhaps most importantly, where does the "hockey stick" belong in a scientific debate about global warming? How can it be used to communicate the science of climate change to the general public and to policy-makers, if at all?