YAD06

YAD061 is a tree in the Yamal Peninsula of Siberia. Its rings provided data used to support Michael Mann's hockey stick interpretation of global climate history. Mann's graph was first published in 1998. It shows global temperatures stable for 900 years until the 20th century, when carbon dioxide emissions caused supposed caused a rapid increase. Other climatologists have suggested that there was a Medieval Warm Period between 950 and 1150 during which the climate was somewhat warmer than it is at present. Although Mann claimed to have used a dozen proxies, analysis showed that only the data from YAD061 had the hockey stick pattern that Mann reported as his result. Mann's graph appeared prominently in the report of the UN's Intergovernmental Panel on Climate Change, used a basis for international policy on climate change. YAD061 has been dubbed, "the most influential tree in the world." Even the cherry-picked YAD061 data did not correspond closely enough to a hockey stick pattern to serve Mann's purpose. It shows a temperature decline since 1960, which is unrepresentative of the pattern of global temperature as a whole. This inconvenient trend was disguised with further manipulation. For the post-1960 period, "Mike [Mann]'s Nature trick of adding in the real temps" was used to "hide the decline," according to the Climategate emails.

In 2013, the Climate Research Unit of the University of East Anglia quietly revised its Yamal data set. The current reconstruction, based on ring data gathered from dozens of trees, shows that temperature in Yamal has been relatively stable for centuries, with no outstanding increase or decrease in the 20th century.