To environmentalists across Australia, it is a baffling anachronism in an era of climate change: the construction of a 4,000-acre mine in New South Wales that will churn out carbon-laden coal for the next 30 years.

The mine’s groundbreaking, in a state forest this year, inspired a veteran to stand in front of a bulldozer and a music teacher to chain himself to a piece of excavation equipment.

But the project had an unlikely financial backer in the United States, whose infusion of cash helped set it in motion: Tom Steyer, the most influential environmentalist in American politics, who has vowed to spend $100 million this year to defeat candidates who oppose policies to combat climate change.

Mr. Steyer, a billionaire former hedge fund manager, emerged this election season as the green-minded answer to Charles G. and David H. Koch, the patrons of conservative Republican politics, after vowing that he would sell off his investments in companies that generate fossil fuels like coal.

But an examination of those investments shows that even after his highly public divestment, the coal-related projects his firm bankrolled will generate tens of millions of tons of carbon pollution for years, if not decades, to come.

Over the past 15 years, Mr. Steyer’s fund, Farallon Capital Management, has pumped hundreds of millions of dollars into companies that operate coal mines and coal-fired power plants from Indonesia to China, records and interviews show.

The expected life span of those facilities, some of which may run through 2030, could cloud Mr. Steyer’s image as an environmental savior and the credibility of his clean-energy message, which has won him access to the highest levels of American government. A few weeks ago, Mr. Steyer, 56, joined President Obama for an intimate group dinner at the White House that ran into the early morning hours, according to people told of the event.

The New York Times examined the operations of coal-mining companies in which Farallon invested or to which it lent money during Mr. Steyer’s stewardship, which coincided with growing demand and prices for coal. Together, those mines have increased their annual production by about 70 million tons since they received money from the hedge fund, according to corporate records, government data and interviews with industry experts.

That is more than the amount of coal consumed annually by Britain.

“I am disappointed, I have to say,” said Dale Jamieson, a professor of environmental studies at New York University, who said he admired Mr. Steyer’s campaign to curb climate change. When it comes to large-scale investments in coal, Professor Jamieson said, “you can’t undo what you’ve done in the past.”

Mr. Steyer sold his ownership stake in Farallon in late 2012, but he has not cut ties with it entirely. He remains a passive investor, his aides said, though they declined to describe the size of his investment. Employees at Farallon screen out any fossil-fuel-related holdings from his portfolio, and he no longer earns a share of the profits from the fund, the aides said.

Farallon is still invested in carbon-generating industries, and the aides declined to say whether Mr. Steyer had asked it to sell those holdings, a request that would presumably hold significant sway given his role as a founder.

The Australian mine, known as Maules Creek, illustrates the complexities of Mr. Steyer’s efforts to distance himself. Farallon was a major investor in a 2009 deal aimed at developing the mine, lending an Australian entrepreneur hundreds of millions of dollars to buy out the previous owner, according to people involved in the transaction. Eventually, the entrepreneur took the mine public, turning Farallon’s investment into a large profit. An executive involved in the original deal estimated that Farallon earned tens of millions of dollars.

Farallon remains an investor in Maules Creek to this day. Mining at the site, expected to start in 2015, will last up to 30 years, yield as much as 13 million tons of coal a year and generate about 30 million tons of carbon dioxide a year, according to Ian Lowe, the former head of the School of Science at Griffith University in Queensland, Australia. (The company that owns the mine, Whitehaven Coal, disputes the carbon dioxide projection.)

Given Mr. Steyer’s reputation as an active environmentalist, Australian opponents of the mine were startled to learn of his firm’s role as an early investor.

“It’s gobsmacking,” Philip Spark, president of the Northern Inland Council for the Environment, a nonprofit trying to stop construction of the mine, said in a telephone interview. “It’s amazing that such a person could have been involved in this project.”

Mark Carnegie, an investment banker in Australia who was involved in the Maules Creek deal, said he could sense even then that Mr. Steyer was struggling to reconcile his motivations as a profit-seeking investor with his growing anxieties about the environment.

But the investment was financially irresistible. “It was a hard thing to turn down,” Mr. Carnegie said. “It was a huge winning bet for Farallon.”

Asked why Mr. Steyer had allowed Farallon to pursue such investments in recent years, Heather Wong, a spokeswoman for Mr. Steyer’s political organization, NextGen Climate, said, “Given how major global funds are structured, they are by definition invested in every sector of the economy, which is why Tom stepped down in 2012.”

When Mr. Steyer founded NextGen Climate in 2013, the environmental movement found what it had long lacked and sorely wanted: a determined political combatant with a willingness to raise and spend campaign money at a level never before seen by traditional environmental groups. An Upper East Side native educated at Yale and Stanford, Mr. Steyer glided through jobs at Morgan Stanley and Goldman Sachs in the 1980s before plunging into the relatively new world of hedge funds. Since he founded it in 1986, Farallon — named for a set of rocky islands off the California coast — has grown to manage as much as $37 billion, from about $15 million in the beginning.

Throughout the early 2000s, the fund offered large, typically high-interest loans to companies seeking to buy undervalued coal mines in Indonesia, which was still rebounding from the Asian financial crisis. The buyouts proved profitable for Farallon, but they also encouraged the new owners of the mines to increase coal production in order to generate revenue to repay the loans, according to executives who participated in the buyouts.

In 2004, for example, Farallon lent at least $60 million to a group of investors buying an Indonesian coal-mining company called Berau, giving the fund a right to a stake in the company, according to people involved in the deal. Within a few years, Berau’s value had doubled, delivering a hefty return for Farallon. Berau quickly sped up its operations: Its coal production soared to 20 million tons in 2012 from about nine million tons in 2004.

Roger Suyama, a former Merrill Lynch banker who was involved in the Berau buyout, said Farallon was “like an anchor in the Indonesian coal industry.”

“By drawing money to an overlooked sector,” he said, “they helped expand the coal industry there.”

As with those in coal mining, Mr. Steyer’s investments in coal-fired power will reverberate far into the future.

Farallon invested in a subsidiary of Indiabulls, an Indian financial conglomerate, in 2008, just as the subsidiary began expanding into coal-fired power. Two years later, Indiabulls began construction on two massive coal-fired power plants: the 2,700-megawatt Amravati plant in central India and the 1,350-megawatt Nasik plant outside Mumbai. When completed, Amravati is expected to be one of the largest coal-fired power plants in India.

Indiabulls has signed a 20-year power purchase agreement with a government-owned electric utility, locking in two decades of carbon pollution. It took a similar approach in China.

In 2007, Farallon provided funds for the sale of Meiya Power, an electric utility that operates four large coal-fired power plants, which collectively produce about 7,000 megawatts of power. Combined, the completed Indiabulls and Meiya plants will produce about 60 million tons of carbon pollution a year, according to Dallas Burtraw, an analyst at Resources for the Future, a research organization in Washington.

The Republican candidates Mr. Steyer is targeting in this year’s midterm elections said such investments deeply undermined his cause.

“It blows a hole in his credibility,” said Representative Cory Gardner, a Senate candidate in Colorado, whose Democratic rival, Senator Mark Udall, has benefited from $100,000 from Mr. Steyer’s political organization. “You can’t claim you are a great environmentalist and invest in the very same technologies you are railing against.”

Republican leaders and their allies are drawing up plans to cast Mr. Steyer as a hypocrite. In North Carolina, Thom Tillis, a Senate candidate, said he intended to portray his opponent, Senator Kay Hagan, and Mr. Steyer as “people who say one thing and do another.”

At the same time, conservative groups and blogs are scouring Mr. Steyer’s business record. One blog, Power Line, has written extensively about Farallon’s work in the coal industry.

In interviews, several prominent environmentalists argued that Mr. Steyer’s unrivaled spending to support climate-change policies outweighed the impact of the carbon pollution unleashed by his past investments.

“This is precisely what we want people to do: sell investments in fossil fuels and get to work solving the problem of climate change,” said Bill McKibben, a founder of the group 350.org, which pushes financial institutions to divest from fossil fuels.

Supporters point to the $25 million campaign Mr. Steyer organized four years ago to defeat a California ballot initiative that would have gutted the state’s landmark climate-change law. The law remained in place and is projected to cut about 30 million tons of carbon emissions by 2020. This year, Mr. Steyer plans to spend four times as much in support of Mr. Obama’s plan to reduce emissions from about 600 coal-fired power plants — a plan expected to eliminate 220 million tons of carbon pollution a year.

But detractors see hypocrisy: As coal linked to Mr. Steyer’s previous investments burns in Asian power plants, he is spending a fortune earned from those investments to pursue a green agenda that would shutter similar plants in the United States.

“If my side wins, it will create real costs for ordinary working people,” said Professor Jamieson of N.Y.U. “Hits to their welfare will not be compensated by stacks of money.”

Unlike Mr. Steyer, he said, “they won’t have options.”

Ms. Wong, the spokeswoman for Mr. Steyer’s political organization, said Mr. Steyer had invested heavily both in creating jobs in the emerging clean-energy industry and in training workers for those positions.

Back in Australia, environmentalists wondered what Mr. Steyer had to say about the giant new coal mine financed by his hedge fund. Would he try to stop it?

Blair Palese, an environmental leader in Australia, urged Mr. Steyer to “get Farallon to step back and get out of this investment.”

“It could be 30 years of coal production,” she said. “How can we keep doing this?”