Tom Steyer, the liberal billionaire behind the climate change-focused SuperPAC NextGen Climate Action, has identified seven key races as part of his $100 million effort. NextGen will pour money and personnel into the Senate races in Colorado, Iowa, Michigan and New Hampshire and the governor's races in Maine, Florida and Pennsylvania, staff told reporters Wednesday. While the four Senate races are among those considered the most vulnerable to flip from Democrat to Republican, NextGen has so far snubbed Sen. Mary Landrieu, D-La., who is in a tight race but has been one of the primary supporters of the Keystone XL pipeline. Steyer, a former hedge fund manager, has pledged to help tip the scales in favor of Democrats who have made climate change a priority issue. He said in a blog post Thursday that holding an "increasingly untenable position" makes climate deniers "unfit for public office." It is the biggest attempt by a liberal donor at bankrolling a massive spending campaign since the Supreme Court's Citizens United ruling that shaped the 2012 elections. The group says it will direct its efforts toward reaching young, female and minority voters, who are the most affected by the threat of climate change, and though they're the most likely to vote Democrat, they're the least likely to turn up to vote in a midterm election. An adviser to Steyer said that he is already looking toward 2016, and will likely get involved in more state races for 2014.