The role human activity plays is not known."[26] Organised campaigning to undermine public trust in climate science is associated with conservative economic policies and backed by industrial interests opposed to the regulation of CO 2 emissions.[27] Climate change denial has been associated with the fossil fuels lobby, the Koch brothers, industry advocates and conservative think tanks, often in the United States.[6][28][29][30] More than 90% of papers sceptical on climate change originate from right-wing think tanks.[31] The total annual income of these climate change counter-movement-organizations is roughly $900 million.[32] Between 2002 and 2010, nearly $120 million (£77 million) was anonymously donated via the Donors Trust and Donors Capital Fund to more than 100 organisations seeking to undermine the public perception of the science on climate change.[33] In 2013 the Center for Media and Democracy reported that the State Policy Network (SPN), an umbrella group of 64 U.S. think tanks, had been lobbying on behalf of major corporations and conservative donors to oppose climate change regulation.[34]