One of the biggest studies to examine how climate change became controversial points to the unified dialogue coming out of the hundreds of individuals and organizations funded by energy heavyweights Exxon Mobil Corp. and the Koch brothers. The study, published Monday in the Proceedings of the National Academy of Sciences, reviewed 20 years of data starting in 1993 to show that climate change-denying groups and individuals who received money from Exxon Mobil and the Koch brothers began to unify their messages in 2007, amplifying supposed uncertainty surrounding the issue. “They were writing things that were different from the contrarian organizations that did not receive corporate funding,” Yale University sociologist and lead study author Justin Farrell said.