London , England ( CNN ) -- The controversy known as `` climategate '' erupted in November 2009 with the publication of more than 1,000 e-mails to and from scientists at the Climatic Research Unit ( CRU ) of the University of East Anglia in eastern England . The e-mails , dating back to 1996 , were published on Web sites run by climate change skeptics who claim efforts had been made to manipulate data to exaggerate the threat of global warming . The head of the CRU , Professor Phil Jones , stepped down from his post while reviews were conducted . It was announced Wednesday that Jones would return to the role of Director of Research at the university after an independent review cleared the CRU of manipulating or falsifying data . `` We concluded that these behaviors did not damage our judgment of the integrity , the honesty , the rigor with which they had operated as scientists , '' said the review 's chairman Muir Russell . In early July , an investigation by Penn State University into one of the authors of the e-mails , Professor Michael Mann , found that he had not strayed from accepted practices for `` proposing , reporting or conducting research . '' Who is the CRU ? The CRU is one of the world 's leading research bodies on natural and human-induced climate change and has developed a number of the data sets widely used in climate research , including the global temperature record used to monitor the state of the climate system . It played a key role in the Intergovernmental Panel on Climate Change 's ( IPCC ) Fourth Assessment Report in 2007 -- a collaboration between the United Nations Environment Program and World Meteorological Organization ( WMO ) -- considered to be the most authoritative report of its kind . Since the e-mail scandal broke , the credibility of the IPCC has been brought into question . In January , the panel admitted its assessment report had wrongly stated that the Himalayan glaciers would disappear by 2035 . How was the climate data allegedly manipulated ? In one particular e-mail , Professor Jones relates to the preparation of a figure for the WMO Statement on the Status of the Global Climate in 1999 . He writes , `` I 've just completed 'Mike 's Nature trick ' of adding in the real temps to each series for the last 20 years ... to hide the decline . '' The alleged 'Climategate ' e-mails . According to critics , this `` trick '' worked in the following way : when temperature readings taken from tree rings showed an apparent decline in temperatures from the 1980s to the present , the researchers added in measurements taken later by more modern instruments , which gave them the answer they wanted . What was the CRU 's response ? In a statement posted on the university 's Web site late last year , the CRU said the use of the word `` trick '' was not intended to imply a deception . It said : `` The requirement for the WMO Statement was for up-to-date evidence showing how temperatures may have changed over the last 1,000 years . `` To produce temperature series that were completely up-to-date ( i.e . through to 1999 ) it was necessary to combine the temperature reconstructions with the instrumental record , because the temperature reconstructions from proxy data ( such as tree rings ) ended many years earlier whereas the instrumental record is updated every month . '' The statement went on to say the illegally obtained e-mails have been `` taken out of context and misinterpreted '' as evidence that CRU manipulated climate data to present an unrealistic picture of global warming . It added that `` this conclusion is entirely unfounded and the evidence from CRU research is entirely consistent with independent evidence assembled by various research groups around the world . '' It called for an independent review to be set up , and since late 2009 , the team , led by Sir Muir Russell , has been examining dozens of submissions . What impact did 'Climategate ' have on the case for global warming ? The e-mails appeared just weeks before the United Nations Conference on Climate Change held in Copenhagen in December 2009 . At the time , many climate change experts claimed the files were stolen in an attempt to undermine the talks . `` Given the wide-ranging nature of change that is likely to be taken in hand , some naturally find it inconvenient to accept its inevitability , '' IPCC chairman Rajendra Pachauri told reporters in the Danish capital . `` The recent incident of stealing the e-mails of scientists at the University of East Anglia shows that some would go to the extent of carrying out illegal acts , perhaps in an attempt to discredit the IPCC . '' After its completion , the December Copenhagen climate conference was widely seen to have failed in its aim of agreeing a global deal on climate change . CNN 's Paul Armstrong contributed to this report .
In November 2009 , more than 200 e - mails were published online . Some skeptics claimed e - mail showed case for global warming had been exaggerated . Independent report on Wednesday cleared them of wrongdoing . Head of unit in question Professor Phil Jones to resign as Director of Research .