(Reuters) - Environmental activist and billionaire Tom Steyer served notice on Monday that he will use his wealth to try to bring climate change into the 2016 U.S. presidential campaign, vowing to target Republican hopefuls who deny the connection between burning fossil fuels and rising global temperatures.

Steyer's NextGen Climate political action committee launched what it calls the Hot Seat campaign aimed at calling out Republican candidates for taking money from the billionaire Koch brothers. The group will target Senator Rand Paul, who is expected to launch his presidential campaign on Tuesday.

Steyer's PAC found limited success turning climate change into a wedge issue in the 2014 midterm elections, despite spending over $70 million on candidates backing strong climate change policies. Only three of seven candidates backed by NextGen won their races.

This time, it hopes to use the conservative Koch brothers as foils, highlighting the connection between their campaign spending and politicians who deny the science underpinning the rise in global temperatures.

"The Koch brothers have emerged as a serious liability for politicians ... making their political influence a critical wedge issue that moves the dial with swing voters and enrages the young voters needed by the GOP to take back the White House," according to NextGen's strategy memo.

The PAC did not disclose spending plans.

NextGen said it will draw from lessons learned from its successful midterm races. In Michigan, for example, NextGen went after the Republican Senate candidate by linking her to the Koch brothers, who were found polluting a river with oil waste they bought from a refinery.

"By following the money trail between the Koch brothers’

unprecedented campaign spending and the specific, local harm that their companies and anti-science policies have inflicted on specific communities, NGC will persuade swing voters and drive key demographic cohorts to the polls," the NextGen memo said.

Outright denial of climate science is becoming an increasingly difficult political position. On Sunday, the Washington Post reported that the American Legislative Exchange Council (ALEC) - a conservative state policy group funded by the Koch brothers - threatened to sue liberal activist groups that accused it of denying climate change.

After several member companies including Google Inc and Facebook Inc left ALEC over its climate position, the group sent a cease-and-desist letter to organizations asking them to "remove misleading material" that suggests it does not believe in climate change.