Standing at the foot of a diesel truck as large as a dinosaur, Andrew Forrest juggled the microphone and then delivered the message that he knew the miners might see as a threat to their jobs and identities.

It was time to go green.

As the sun set over the hills of the first mine that set him on a path to enormous wealth, he explained that Fortescue, the Australian company he founded, would no longer just extract and ship 180 million tons of iron ore, the raw material for steel. It would zero out its own carbon emissions and become a renewable energy powerhouse.

“Global warming, all of you know, is really serious, and it’s accelerating a lot quicker than anybody thought,” said Dr. Forrest, 59, delivering what sounded like a general’s pre-attack briefing. He told the troops — which is what he calls the workers, whom he tries to visit every few months as Fortescue’s chairman and largest shareholder — that everyone else, the government, the other big mining companies, just talked around the problem.

“What you’ll be doing,” he said, scanning the faces of miners and mechanics covered in engine oil, “will be stacks of what you’re best at, which is action. You guys are going to be at the forefront of turning the world green.”

He gave his speech two months ago in the Pilbara, Australia’s mineral heartland. A remote, “Mad Max” desert more associated with rust than recycling, it’s where Fortescue made $10.3 billion in profit last year by extracting iron ore and selling it mostly to Chinese steel makers. Along the way, the company burned through 700 million liters of diesel and released 2.2 million tons of greenhouse gases — more than some small countries.

But Dr. Forrest had come to the Cloudbreak mine to paint a cleaner portrait. He told the workers that when they reached their rocking chairs in retirement, they’d tell their grandchildren that they had helped change the world. Trying to make sure they would embrace the mission, he told them that climate innovation would save their jobs, and as proof, he promised to deliver hydrogen-fueled haul trucks next year followed by drills, trains and processing plants all running on renewable energy.

Many of the workers nodded. One tossed out a question: “Are we going to get any specialized training?”

“Yeah, you will,” Dr. Forrest said.

Turning promises into tangible results — that would be the tough part. His company employs 15,000 people and is worth more than $30 billion. He could lose it all if his plan to decarbonize by 2030 and diversify into energy goes wrong. He is essentially gambling with the stable mining company that has made him one of Australia’s richest men. He wants it to become a high-tech start-up producing five times more renewable energy than the Australian power grid and selling hydrogen to the world’s factories and mills.

His vision is built on the audacious idea that a maverick from a resource-rich corner of the Earth can do what has not been done — reform manufacturing, stymie Big Oil and help save us all from climate catastrophe. And he wants to do it with a hulking old industry that is usually vilified at climate conferences.

In many ways, the criticism makes sense: The iron and steel sector emits around 7 percent of the world’s carbon dioxide (more than all of the world’s cars). And unlike coal, it can’t be phased out unless we no longer want new appliances or buildings. Wrenching transformation is really the only option if international climate goals are to be met.

Dr. Forrest is either the most or least likely person to pull it off. He earned a Ph.D. in marine ecology two years ago, spurring a desire to do more on climate change, and he announced his crusade after the worst wildfires in Australia’s recorded history. But he’s no typical greenie. He talks more about freedom than carbon taxes. Climate activists were skeptical at first. Now they’re hoping he succeeds.

Michael E. Mann, a prominent American climate scientist who has long been a vocal critic of carbon-heavy companies that he calls “inactivists,” argues that cleaning up a major mining company like Fortescue would be hugely important for a few reasons. It would not only slash emissions. It would also show that it’s possible for even the biggest emitters to make money while improving the health of the planet.

“Such efforts are critical to addressing climate change in the window we have,” Dr. Mann said.

Dr. Forrest knows that the magnitude of the task means he might fail. But in part because of what he has already accomplished, he believes anything is possible — and he lives out that belief with a zeal he exhibits in relaxed moments, too. On his plane, during a tricky takeoff or when everyone needs an emotional lift, he stands in the aisle and sings along to his favorite song: Tom Petty’s “Runnin’ Down a Dream.”

‘It’s the Sound of the Future’

The search for climate salvation begins in northwestern Australia, in the rolling hills of the Pilbara, a region bigger than California that produces a third of the world’s iron ore. It’s a desert of quiet, relative emptiness with clusters of a few thousand people at mine sites marked by a cloud of reddish dust in the day and flashes of yellow lights at night.

On a drive around Solomon, Fortescue’s most productive mine, Dr. Forrest could barely contain his love for the Pilbara’s mix of natural beauty and human ingenuity.

“Stop looking at your screens,” he shouted at one point, gesturing out the bus window to make sure that the employees he had brought along from urban offices shared his enthusiasm. “Look at the scale of this.”

He called the tangle of belts and beams at the ore processing plant “a beautiful piece of kit.” He could easily imagine windmills and solar panels in the Pilbara. They would create the electricity needed to turn water into hydrogen, and that green hydrogen could travel the same routes as iron ore, gas or coal — fueling factories in the United States, steel mills in Europe and Fortescue’s own trucks and trains.

Better yet, Fortescue could use the green energy to power its own steel production.

That’s the dream he’s running down both in the Pilbara and nearly 1,000 miles away, at a pair of labs in Perth, where he had already put together teams to build the infrastructure he could see in his mind.

The most groundbreaking developments have come from a small room at the University of Western Australia, Dr. Forrest’s alma mater, where the company’s electrochemists have found a new route to what’s known as green iron and steel.

Nearly 90 percent of the carbon released by the steel-making process comes from reducing it to “pig iron” in a blast furnace or smelter powered by fossil fuels. Fortescue’s engineers have built a miniature mill that they said could do the same thing with electrodes and a pressurized brew of metals and other materials. Sitting on a counter, it resembled a water heater crossed with an espresso machine.

At least one other company, Boston Metal, which counts Bill Gates as an investor, has found a way to do something similar. But Fortescue’s scientists say they’ve figured out a process that works at lower temperatures (no hotter than a cup of coffee), allowing for easy on and off cycles with intermittent, renewable energy.

The group’s design, secret until now, recently received provisional patent protection.

That burst of innovation — and the pace of improvement at Fortescue and elsewhere — is one of many factors bolstering Dr. Forrest’s optimism. He believes Fortescue can take advantage of technologies that have come down in price (around solar and batteries, for example) while pushing green development further, faster, by building equipment that the company can test and use in its own operations.

“Andrew has three things going for him,” said Malcolm Turnbull, a former Australian prime minister, who has known Dr. Forrest for 25 years and recently teamed up with him to support green hydrogen. “One, he’s passionately committed to the energy transformation. Two, he’s got enormous financial resources. More than a few people can tick those boxes, but the third box is that he is the founder and chairman of a company that has engineering and construction in its DNA.”

Dr. Forrest studied commerce at university and worked as a stockbroker in the 1980s, but at Fortescue, he put a priority on the innovation of things, from covered conveyor belts to driverless trucks. Similarly, since forming Fortescue Future Industries, a subsidiary funded with 10 percent of the parent company’s profits, Dr. Forrest has hired dozens of scientists and invested in their designs.

Green steel, formed entirely with renewable energy, is the Fortescue moonshot.

“It will be a winner-take-all market,” said Saul Griffith, an electrification expert (and MacArthur fellow) who started his career at an Australian steel mill. “You can’t spend enough in the race to have the first electrochemistry pathway to steel.”

But scaling up is the problem not just there; it’s the challenge with everything Dr. Forrest is trying to accomplish, including Fortescue’s most immediate hurdle — transportation. Half the company’s emissions come from its diesel-guzzling fleet.

At a giant garage in an industrial area called Hazelmere near Perth’s airport, around 100 experts in engines and energy are trying to eliminate all that carbon by turning a mining company into a clean, green version of Caterpillar or John Deere.

When I visited, Dr. Forrest had asked a few new employees and people who work with his charity, the Minderoo Foundation, to come along. Everyone was especially excited to see the same thing: the hydrogen-fueled haul truck. When it pulled into the midday sun, painted blue and white, it looked far too clean but as imposing as any other truck, with a few alterations.

Jim Herring, the head of green industry for Fortescue Future Industries and a former mine manager who had been in charge of deploying driverless trucks, pointed to a hydrogen cylinder and a wall of batteries placed where the diesel fuel tank had been removed.

“The team literally built this thing in 100 days,” he said.

Using available equipment, the truck could run for only about 20 minutes. They need it to run for 20 hours.

“Our goal,” Mr. Herring added, “is to have this truck deployed, running on the mine site in 23 months — well, we have 22½ months now — which is about five years sooner than everyone else.”

Dr. Forrest encouraged me to climb aboard. Inside the cab, I met Sean Kelly. He was the driver, an electrician with an accent as thick as his mustache. His nickname: Mad Dog. He told me that he was thrilled to be part of something new.

“I’ve been in mining for 20 years,” he said. “Nothing has really changed until now.”

As he drove around, a computer screen showed power distribution for the battery and the fuel cell and the revolutions per minute for the motor. A warning section had the word “flame” — hydrogen burns clear, so an infrared camera with an alarm system had been added.

It was a small sign of the technical challenges ahead. Hydrogen is more explosive than diesel and difficult to store whether it’s formed by splitting water with renewable electricity (that’s green hydrogen) or by separating hydrogen from coal and gas (brown, gray and blue hydrogen), which emits a lot of carbon.

Mad Dog turned left and revved the engine as we approached Dr. Forrest. The monstrous truck, requiring a ladder to get over the tires, hummed like a server farm and released only steam in puffs of white.

“It’s the sound of the future,” Dr. Forrest said. Holding a microphone, he seemed eager to hug anyone who came near him.

“Silence is so exciting,” he told me. A few minutes later, as he leaned out of a BMW’s back seat, his fervor only seemed to increase.

“It’s like being there at the beginning of the industrial revolution,” he shouted out the window. “Someday you’ll look back and say, ‘I was there.’”

‘Confessions of a Carbon Emitter’

The posters went up in every camp. Along with flies and dust, the workers building Fortescue’s 160-mile railway were greeted each morning with the photo of a man in a suit standing on the tracks above a question: “Ever wanted to flatten a banker?”

It was not a call to violence from Dr. Forrest for his tired crews but rather a vote of confidence. He had hoped to bring Fortescue’s ore to market by connecting with the railway and port of a large competitor, BHP, but in 2006, the company refused, forcing him to scramble for permits and land rights. A few months later, one financial analyst was so certain the venture would fail that he said he’d be happy to be chained to the tracks along Fortescue’s proposed route “because I know I will not be killed by a train.”

Dr. Forrest put his quote at the top of the poster.

“When I go into a fight, I need a Goliath,” he told me. “It’s about steeling my team.”

In Australian business circles, Dr. Forrest is known for being a salesman of the impossible, sometimes prone to hyperbole but often proving the skeptics wrong.

The way he tells it, a taste for risk runs in the family.

His great-uncle John Forrest was one of the first surveyors to cross Australia’s inhospitable interior in 1869, mostly on foot. He went on to become the first premier for the state of Western Australia, where he is still celebrated for pushing through a public works project that pumped water 500 miles inland, uphill, to the state’s newly developed gold mines.

The story appears in a book that Fortescue published for employees, under a heading: “in the blood.” Dr. Forrest retold the tale in his first speech announcing his plan to overhaul Fortescue, given in January as part of a public lecture series under the title “Confessions of a Carbon Emitter.”

“The logistics were formidable then,” he said in the speech. And it’s the same today, he added, with naysayers insisting that going green is too daunting or costly.

It requires a thick hide, as he puts it, arguing that he developed exactly that at the Forrest homestead of Minderoo. The pastoral station is vast and majestic, set along the Ashburton River, but it was far from luxurious when Andrew was born in 1961. His mother, Judy, learned to fly a plane to muster sheep. His father said little and demanded a lot.

By the time he went to boarding school in Perth, where the Forrest name seemed to shout from street signs, he was scrawny but quick with a punch. Twiggy became his nickname. He also stuttered — until he joined the high school debating team.

“I thought that if I can do that, I can get over my stutter,” he said. “It was like a blood sport.”

The same might be said of mining. When he started Fortescue in 2003, he had already tried and failed once, being pushed out of Anaconda Nickel, a company he had spent nearly a decade trying to build.

The battle took a lot out of Dr. Forrest and tarnished his name. Disputes over deals made their way to court, and in one case, a state judge suggested that he had been untruthful. Critics and creditors said he was all bluster, not enough expertise.

His supporters interpreted the Anaconda affair as an example of Australia’s egalitarian tendency to cut down “tall poppies” — those who do not conform. Anaconda’s Murrin Murrin mine project went on to become one of the most successful nickel and cobalt operations in the world, and Dr. Forrest still believes he was right about the company’s promise. What he got wrong was whom to trust.

“Anaconda taught him the importance of keeping control,” said Nicola Forrest, his wife of 30 years.

Fortescue proved to be a bigger challenge than Anaconda. The new company relied on leases that the industry leaders (BHP and Rio Tinto) overlooked and spent more than $100 million on exploration in its first two years, running up debt. At Cloudbreak and its sister site, Christmas Creek, Fortescue drilled nearly 9,000 holes.

As soon as the company had the geology confirmed and secured customers in China — where steel mills were hungry for new sources of iron ore — it moved quickly to production. From around 2006 to 2008, the company built a new mine capable of producing 45 million tons of iron ore per year, along with the railway connected to Port Hedland, where the ore is gathered and loaded onto ships.

“They have a track record of building a very large-scale project in a very short period of time,” said Camille Simeon, investment director for Australian equities at Abrdn, which is not a Fortescue shareholder. “They’ve been incredibly nimble.”

After shuttling visitors on a two-day tour of the mines, Dr. Forrest met his wife off the coast of Exmouth on his 191-foot superyacht, Pangaea. He had turned it into an oceanic research vessel, though the dark wood and display cases inside (from the previous owner) created a vibe that Mrs. Forrest called “‘Jumanji’ mixed with the Museum of Natural History.”

Over a dinner of steaks from Harvey Beef, a company the Forrests’ private investment firm bought a few years ago, he and Mrs. Forrest told the full story of the Fortescue train line — a turning point for the company — and tried to unlock the puzzle of motivation. Shaking his head, wincing at times, Dr. Forrest seemed uncertain. Did he really need an enemy? Was he still a David fighting Goliaths now that he was worth $20 billion?

“People want solutions,” said Mrs. Forrest, a daughter of farmers who plays a large role in the family’s philanthropy efforts. “It’s all fine to talk doom and gloom.”

She turned to her husband. “You’re talking about finding the way through it,” she said. “You’re helping people see the long way, the outcome.”

The next morning, Dr. Forrest appeared in a white bathrobe, sounding more certain. He pulled out a blue hardcover book — his Ph.D. thesis from 2019 at the University of Western Australia: “Pelagic Ecology and Solutions for a Troubled Ocean.”

He told me that he first started thinking about climate change five years ago, when he stepped back from day-to-day operations at Fortescue and started his Ph.D. He had always loved the ocean, but he became saddened by his own research showing that sharks and other marine life were disrupted because their environment lacked oxygen.

“Fish populations were moving to find air to breathe, not to eat,” he said. “And that’s global warming.”

The discovery pushed him to do more. He recalled something his mother had told him: “Enjoy your life, but make sure you’re as useful as you can possibly be.”

He had already pledged to give away the majority of his fortune. What he dreams of now seems to be a moral or ethical version of the entrepreneurial process.

“It’s scalable goodness,” he said.

‘If You Are Responsible, You Must Act’

Inside a cavernous warehouse in Port Hedland where a mechanical unloader dumps 15,000 tons of iron ore out of passing train cars every hour, Fortescue’s transformation is already starting. In the thunderous noise and heat, Stephen Dansie, the manager of maintenance, said his team was preparing for a switch to green energy.

“Whether it’s battery, ammonia or hydrogen, we’re going to have to change our maintenance strategies,” Mr. Dansie said. “We’re reviewing all of it.”

Dr. Forrest is asking a lot of his company’s employees, not to mention investors, officials and allies in the fight to get climate change under control. Even those who hope he succeeds question if he and his team will stay committed.

“If they spend a billion dollars over the next few years trying to get this thing off the ground and it doesn’t work, are they going to pull the plug?” asked Dan Gocher, climate director at the Australasian Center for Corporate Responsibility.

Dr. Forrest is aware of the pressure and the doubt. When I asked whom he needed to convince to make sure his dream became reality, he answered quickly: “Everyone.”

Miners, it turned out, were the easiest ones to persuade. At the sites I visited with Dr. Forrest, I interviewed dozens of workers and contractors. Nearly all expressed relief: Finally, they said, they could participate in a solution to climate change, getting past tired culture war politics.

At Cloudbreak, William Webster, 27, the diesel mechanic who asked about training, said he was looking forward to seeing how the hydrogen trucks worked.

At the other mines and at Port Hedland, there was even more excitement.

“It’s revolutionary,” said Nick Sanders, 27, an auto electrician at Solomon. “It puts us ahead of every other mining company.”

In interviews, Dr. Forrest said he was still working on the Australian government. The country’s conservative prime minister, Scott Morrison, has resisted committing to ambitious emissions targets despite pressure from the United States and a visit to Cloudbreak, where miners told him to get on board with going green.

Dr. Forrest also complained about the Labor government in his own state of Western Australia, which had yet to create a legal framework for developing renewable energy on pastoral land.

“Industry is really leading here, and the government is coming along behind,” said Madeline Taylor, a senior lecturer in environmental law at Macquarie University in Sydney. “It’s the cart pulling the horse.”

(Mark McGowan, the premier of Western Australia, declined to be interviewed. Mr. Morrison’s office did not respond to questions sent by email.)

On the way to Minderoo for an off-site meeting with Fortescue Future Industries’ executives and board members, Dr. Forrest admitted that the stress of waiting for allies wore him down.

“Nobody knows what a high-wire act it really is,” he said on the plane. “You make a bet” — he threw down his hand as if tossing cash on a table — “and you feel it. I worry about it. First you have a few people, then you have a few thousand.”

Many of those elevated to share the challenge first proved their worth in familiar territory. Julie Shuttleworth, FFI’s chief executive, was the general manager at Cloudbreak and then Solomon before serving as the deputy chief executive of Fortescue. She also describes herself as a nature lover who hates seeing a single tree chopped down.

At the Minderoo “think tank,” she and the rest of the group had a lot to discuss. The company had already set an ambitious goal of supplying over 15 million tonnes (16.5 million tons) of green hydrogen annually by 2030, more than the entire world currently produces. Investors and climate activists were eager to see progress.

To get going, FFI expects to spend $400 million to $600 million in the fiscal year that started in July, and in one of the first meetings, people online and in the room flipped through a lengthy document listing potential investments. In a little over six months, they had identified 130 renewable energy opportunities in around 60 countries, including 30 they thought could be pursued before 2031.

In the meeting, Ms. Shuttleworth highlighted projects that could be developed as soon as possible. About half were overseas, half closer to home.

“What I’m hearing,” Dr. Forrest said, “is that Australia is not a total disaster.”

He’d soon be proved right: FFI recently announced plans to build hydrogen production plants in Queensland and New South Wales, with the latter benefiting from a new state strategy of tax breaks and grants for green hydrogen.

Outside politics, the uncertainties looked harder to manage. Dr. Forrest pressed the team to get manufacturing costs down by 40 percent. He also emphasized the need to rally support before and during the United Nations’ COP26 climate conference in Scotland next month, to keep the natural gas industry from gaining more of an upper hand.

“We have to get to a point where everyone realizes blue hydrogen is a con,” Dr. Forrest said. “It’s no better than fossil fuels.”

Eventually, the group landed on specific goals. By Dec. 15, Mr. Herring agreed to have a road map for decarbonizing trains, ships and mining equipment so they would be ready to operate in 2022. As a group, they also finalized plans on their top 10 solar and wind projects. Five had no clear title but needed to get done.

After the day’s last meeting, walking near a room filled with photos of his great-uncle, Dr. Forrest said he needed to find a pathway to wealth for the company. Novelty becomes legacy only when others buy in and benefit.

“If it’s not profitable, we’ll have no followers,” he said. “We need to hold ourselves up as an example.”

The sun was setting over the Ashburton River. It was nearly time for dinner — on a bridge built a century ago out of concrete and steel.

A long, narrow table had been set up in the middle, with views up and down the river. After glasses of Spanish cava, Dr. Forrest announced that they were all part of another first — the first time dinner had been served on the bridge.

As plates of paella appeared, a Fortescue tradition commenced, with speeches from everyone. None of the toasts cited temperature rise or biodiversity or drought. Mostly, the group seemed energized by engineering and adventure.

Michael Dolan, a hydrogen scientist, spoke about a recent whirlwind world tour with Dr. Forrest, including a lunch with Bill Gates after a long night with too many drinks. Gordon Cowe, FFI’s director of development and projects, said he had returned to Fortescue after many years away, working for the fossil fuel industry, because “it’s time for a reversal.”

Dr. Forrest spoke last. As he looked from one length of the bridge to another, it suddenly became clear that he had chosen the location for its narrative potential. Pointing to the far end, behind him, he said that side represented the resistance to their climate change plans — it was the old way of doing things. In his view, those who came from there had no cause for shame.

But, he said, it was time to move on. He pointed forward, toward what he saw as humanity’s promising future, and said: “That side is where we must go.”

In between was Fortescue.

“If you are responsible, you must act,” Dr. Forrest said.

A pair of galahs, loud pink-bellied cockatoos native to Australia, flew overhead, providing a natural chorus. Everyone at the table fell silent. But one seat was empty.

Ms. Shuttleworth hadn’t made it to the end of the evening. Halfway through, she stood to leave. Fortescue Future Industries — the bridge, in Dr. Forrest’s metaphor — just signed a deal for a wind farm in Argentina. She needed to thank local officials for agreeing to be a part of the future that Fortescue envisioned.