Conservative billionaires used a secretive funding route to channel nearly $120m (£77m) to more than 100 groups casting doubt about the science behind climate change, the Guardian has learned.

The funds, doled out between 2002 and 2010, helped build a vast network of thinktanks and activist groups working to a single purpose: to redefine climate change from neutral scientific fact to a highly polarising "wedge issue" for hardcore conservatives.