A prominent US climate scientist at the centre of the "climategate" leaked email controversy has been virtually cleared of professional misconduct by an internal university enquiry. Michael Mann, of Penn State University, featured regularly in the more than 1000 emails that were hacked from the University of East Anglia in the UK last November. His emails and comments have since then featured in countless blogs and news articles. Some have claimed the emails reveal that mainstream climate scientists have massaged data in order to demonstrate that climate change is caused by human activities. The scientists in the emails, including Mann,...