The Intergovernmental Panel on Climate Change (IPCC) draft report says that ”it is extremely likely that human activities have caused more than half of the observed increase in global average surface temperatures since the 1950s.” According to the report carbon dioxide concentrations in the atmosphere are the highest in 800,000 years.
http://www.reuters.com/article/2012/12/14/us-climate-ipcc-idUSBRE8BD0VV20121214