The material comprised more than 1,000 emails, 2,000 documents, as well as commented source code pertaining to climate-change research, covering the period from 1996 to 2009.[28] According to an analysis in The Guardian, the vast majority of the emails were from or to four climatologists: Phil Jones, the head of the CRU; Keith Briffa, a CRU climatologist specialising in tree ring analysis; Tim Osb