The two senators, both likely contenders for the 2016 presidential race were voting against an amendment offered up by Vermont independent Bernie Sanders. Democrats have repeatedly offered up such amendments—which in the current Senate have no chance of passing—in order to highlight Republicans' positions on climate change, betting it will repel swing voters.
Indeed, nearly all of the Senate's 54 Republicans voted against the amendment. The five exceptions: Kelly Ayotte, Susan Collins, Lindsey Graham, Mark Kirk, and Rob Portman—all of whom voted for the amendment. Ayotte, Kirk, and Portman all face contested races in purple states in 2016, while Graham is eyeing a White House bid and has been one of few Senate Republicans urging action to address climate change.
The vast majority of scientists say that global warming is real and caused by human activity, but public opinion is divided and endorsing climate science can land Republicans in hot water with their base.