Even in a state long considered the unregulated Wild West of campaign finance, the Pennsylvania megabucks plan by Steyer's NextGen Climate - part of a $100 million crusade to make climate change a "wedge issue" in seven key races - is unprecedented, and stunning in its scope. It may exceed - in both size and impact - the $10 million of Wolf's own dollars that propelled him to the Democratic nomination last month.
Although Steyer's $100 million gamble makes him the liberal alt-universe anti-Koch of 2014 politics, unanswered questions loom:
How much will citizens really care about climate change when they enter the voting booth? And here in Pennsylvania, will the inevitable GOP counterattacks on Steyer and his chosen candidate Wolf as "job crushers" for coal and for fracking natural gas end up stinging the Democrats?
"The fact is that voters don't look at climate change as an issue," said G. Terry Madonna, a Franklin & Marshall College political scientist and pollster. He said polls show that Pennsylvanians care about down-to-earth environmental matters - majorities support taxing the fracking industry and oppose drilling on state parkland - but not as much as they care about the bread-and-butter issues of jobs and education.
A March survey by the Robert Morris University Polling Institute found that 55 percent of state residents believe that tax dollars should be redirected to help reduce global warming.
Steyer, 56, hopes to build on that. Worth at least $1.4 billion from running the innovative Farallon Capital Management hedge fund in San Francisco, Steyer joined Bill Gates, Warren Buffett and other billionaires in 2010 in pledging to give at least half his wealth to worthy causes; his No. 1 cause is fighting climate change by promoting more use of renewable energy and less of fossil fuels.
Steyer, a top foe of the Keystone XL oil pipeline, told the New Yorker that curbing global warming is "the issue we'll get measured by as a country and a generation," and last year he spent $11 million to help the Democrats and Terry McAuliffe retake the Virginia governor's mansion.
This year, Steyer plans to donate $50 million and to raise another $50 million to spend on seven key races - involving incumbent GOP governors in Maine, Florida and Pennsylvania, and contested Senate races in Iowa, Michigan, Colorado and New Hampshire. In each case, the goal of his NextGen Climate is to defeat a Republican perceived as weak on climate change, or who denies that global warming is even occurring.
'A pivotal year'
Chris Lehane, Steyer's chief political strategist who was Al Gore's campaign press secretary in the 2000 presidential race, said that "2014 will be a pivotal year when it comes to this issue. Can you employ climate as an 'edge' political issue? Can it help you win an election?"
Lehane promised that NextGen Climate won't be a "drive-by PAC" just running TV ads, but hopes to organize voters in the field, especially on college campuses, where so-called "millennials" voice concern about climate change. The group also seeks to organize inner-city voters around high rates of asthma linked to air pollution, and to hold events around local pollution issues. Young and minority voters lean Democratic, but have low turnout rates in non-presidential years.
The group plans to slam Corbett for his statements on global warming - he called it "a subject of debate" earlier this year - and for appointing Cabinet secretaries who've questioned climate science, for taking at least $1.7 million in contributions from oil and gas firms and for opposing the fracking tax.
But Billy Pitman, a Corbett campaign spokesman, said the governor is not a denier of climate science and promotes policies - especially increased use of natural gas but also clean coal - that have reduced Pennsylvania's carbon emissions.
'Ultraliberal . . . radical'
The Marcellus Shale Coalition, which promotes the fracking industry, was harsher. Said spokesman Travis Windle: "Ultraliberal San Francisco billionaire Tom Steyer's mission is clear: Seek-and-destroy energy and manufacturing jobs. His dangerously out-of-touch, radical policies will be rejected wholesale in our commonwealth."
Interestingly, Wolf's people aren't doing a victory dance over the expected cash - although campaign spokesman Mark Nicastre said that with "Corbett's decision to let the oil and gas companies get away with making millions while charging no severance tax, we're not surprised to hear that Mr. Steyer is focusing on Pennsylvania."
He said that in addition to supporting a tax on fracking, Wolf promises to promote green energy such as wind and solar, and to appoint Cabinet secretaries who take climate change seriously.
On Twitter: @Will_Bunch