While an adjunct assistant professor at the University of Massachusetts Amherst , Michael E. Mann co-authored with Raymond S. Bradley and Malcolm K. Hughes two reconstructions of the past temperatures in the northern hemisphere : MBH98 and MBH99 . The latter extended back 1,000 years and was nicknamed the " hockey stick graph " . In 1999 Mann joined the University of Virginia as an assistant professor . A version of MBH99 featured prominently in the 2001 IPCC Third Assessment Report , and attacks on the graph by those opposing action on global warming became politically prominent in the Hockey stick controversy . The validity of the research was confirmed by the National Academy of Sciences . In 2005 Mann moved on to a position as an associate professor at Pennsylvania State University . The Climatic Research Unit email controversy which began in November 2009 brought renewed scrutiny , and allegations of scientific malpractice . An investigation by Pennsylvania State University determined on 3 February 2010 that there was no evidence of misconduct by Mann
Climatic Research Unit email controversy
Climatic Research Unit email controversy
Attorney General of Virginia's climate science investigation