Billionaire retired investor Tom Steyer has pledged to spend at least $50 million of his fortune making climate change an election issue this year and is trying to entice other wealthy donors to put up another $50 million.

So far he has been alone in writing checks to his climate-themed political organization, NextGen Climate Action Committee.

To change that, he gathered about 20 prospective donors and money-raisers at his California ranch earlier this month and made the $100 million pitch, two people familiar with the meeting confirmed. The money would be used to support candidates who want to address climate change in ways that Steyer backs, including opposing the Keystone XL pipeline to transport oil sands from Canada through the U.S.

“There is an army building, and it’s not going to be Tom alone,” said Betsy Taylor, who runs a consulting group in Takoma Park, Maryland, on climate strategies and attended the meeting at Steyer’s ranch. She compared Steyer’s effort to that of the fictional hero Harry Potter, who built Dumbledore’s Army to defend against the Dark Arts in the popular movies and children’s books by J.K. Rowling.

The group discussed getting involved in both state and federal elections, including the New Hampshire senate race, where Democratic incumbent Jeanne Shaheen could face former Republican Massachusetts Senator Scott Brown, who recently moved there, Taylor said. In earlier races, Brown expressed skepticism about climate change being a result of human activity.

Governor Races

Steyer also is considering gubernatorial races in Pennsylvania and Florida, where Democratic candidates have a shot at unseating Republicans who haven’t promoted climate issues.

“Steyer is going into states where climate really matters,” Taylor said. “They are looking for places where there is a kind of clarity.”

The 56-year-old, whose net worth is $2.6 billion, according to the Bloomberg Billionaires Index, made his fortune as a money manager. He founded and was former chief executive of Farallon Capital Management in San Francisco.

Steyer has pledged to give away all of his wealth and intends to spend much of it on climate change, he has said in previous interviews. He told The New York Times, which first reported NextGen’s $100 million fundraising goal, that his personal investment in politics could well surpass that sum. Steyer is likely to invest in 2014 campaigns, even if he fails to lure other donors to meet his challenge.

Campaign Activity

In the past two years, Steyer has stepped up his political activism.

He spent more than $50 million on a successful 2012 California ballot initiative to rescind a tax benefit given to out-of-state companies, on Massachusetts Senator Ed Markey’s special election victory, and on Democrat Terry McAuliffe’s winning race for Virginia governor.

Part of his spending was funneled through NextGen, a super-political action committee that can raise and spend unlimited sums of money so long as there’s no coordination with candidates. Steyer started the super-PAC seven months ago and put $9.3 million into it by the end of the year, Federal Election Commission records show.

The super-PAC has spent its money on television advertisements, airplane banners, mobile billboards, polling and public relations. It didn’t pay for fundraising consultants or money drives, and the group’s website has no mechanism for contributions.

Fundraising Aptitude

NextGen officials wouldn’t say whether Steyer’s initial meeting this month resulted in any financial commitments.

Steyer has shown an aptitude for raising political money for party causes and candidates.

Tomorrow, he’ll host at his San Francisco home a fundraiser for the Democratic Senatorial Campaign Committee, which is trying to help the party maintain its slim majority. Republicans need a net gain of six seats to wrest control of the Senate.

At that fundraiser, attended by some senators who agree with Steyer’s focus on climate change, he will share new polling on Keystone. The survey also shows how support for the pipeline is affected by certain elements such as Chinese investment and whether the oil will stay in the U.S.

Steyer will then fly to Washington, D.C., for the Democratic Governors Association winter conference, where he will join a Feb. 21 panel discussion on climate change, according to a DGA agenda. Also on the panel are McAuliffe, Maryland Governor Martin O’Malley, Washington State Governor Jay Inslee, Connecticut Governor Dannel Malloy and Vermont Governor Peter Shumlin, the DGA chairman, according to the agenda.

The discussion group will cover ways state leaders can advance regional greenhouse gas initiatives as some New England states have done in the absence of congressional involvement.