AMNA NAWAZ: This week, a group of countries may approve what's widely seen as the first carbon tax on the global shipping industry.

The International Maritime Organization is poised to approve new levies on ships for their emissions.

Payments would become mandatory near the end of the decade and are designed to get companies to cut back emissions substantially by mid-century.

But the Trump administration argues it's a harmful tax and is threatening tariffs.

William Brangham has a look now at a key business player who's attracting attention for his efforts to make that industry and others greener.

WILLIAM BRANGHAM: Sailing into New York Harbor, it may look unremarkable, but the Green Pioneer is a ship with a difference.

It's the first cargo ship partially powered by green ammonia, a carbon-free fuel that some say could help decarbonize the notoriously dirty global shipping industry.

That industry's traffic makes up 3 percent of all greenhouse gas emissions, which is more than double the pollution of France or England.

ANDREW FORREST, Founder and Executive Chairman, Fortescue: We can get sun, wind, water, or you get to make ammonia.

That's it.

WILLIAM BRANGHAM: Australian billionaire Andrew Forrest is the force behind the Green Pioneer, and he is a surprising climate activist.

Forrest runs Fortescue, one of the world's largest iron ore mining companies.

But three years ago, he pledged to eliminate nearly all carbon emissions from his operations by 2030.

ANDREW FORREST: As soon as we worked out that there is a way and that technology development was totally on our side, but we could go, if you like, fully green, we could stop burning fossil fuel, there are economically powerful, profitable solutions for you to stop burning fossil fuel.

So why keep doing it?

WILLIAM BRANGHAM: Forrest now travels the world, evangelizing this message, meeting with everyone from legendary oceanographer Sylvia Earle to world leaders.

That included a stop last month in New York during the United Nations General Assembly, where he publicly criticized President Trump's speech to the U.N., where Trump belittled the facts of climate change and efforts to address it.

DONALD TRUMP, President of the United States: Climate change, it's the greatest con job ever perpetrated on the world, in my opinion.

If you don't get away from this green scam, your country is going to fail.

ANDREW FORREST: I want to say to the president, you had no basis of fact to make that statement.

No matter how many times someone must repeat a lie, it doesn't change it to a truth.

It's still a lie.

And I don't mean my comments to be offensive.

I think you will see the adoption of green energy simply because it's in the best interest of the American people to have a lower cost of power so, for the same money, they can have a higher standard of living.

WILLIAM BRANGHAM: At Fortescue, Forrest is deploying the full suite of renewable technologies, including solar and wind farms, newly engineered battery-powered trains and long-haul trucks.

The company just announced layoffs in the U.K.

and Australia and will instead outsource more from other countries, including China.

ANDREW FORREST: Not going to be an easy task.

WILLIAM BRANGHAM: Forrest is frequently attacked by other mining and fossil fuel interests for his stance on green energy.

He was also just mentioned in a defamation case brought by ExxonMobil in California, where the oil giant is suing the state and some activist groups he funds of smearing the company.

ANDREW FORREST: Well, look, I would say to my critics, your criticism is fine.

It makes you stronger.

It's not going to change our course.

We have everything on our side.

All you can do is hide the truth, OK?

The truth is going to win out.

You might delay it.

But that's the best you can do.

Ready to roll?

WILLIAM BRANGHAM: So how did a mining executive, a man whose past carbon footprint is likely bigger than some small island nations, end up a climate advocate?

Forrest says it was two things.

One, after studying for a Ph.D.

in ocean ecology a decade ago, he learned the true extent of the climate crisis.

And, two, the rapid evolution of green energy technology convinced the capitalist in him that he could make a difference and make a profit.

ANDREW FORREST: All of this ecosystem of creating 24/7 energy, but the cheapest in human history, unapologetically green.

Why green?

Not because we're woke, but because we are ruthlessly good businesspeople, and we are taking the best choice to create the greatest margin for our shareholders and our countries.

WILLIAM BRANGHAM: Sailing his ammonia-powered ship into New York was another part of Forrest clean energy pitch.

He also wanted to pressure delegates who were about to vote at the International Maritime Organization, the IMO, on new binding clean emissions standards for the shipping industry.

The Trump administration has been trying to block them, arguing they would help China and harm U.S.

consumers.

ANDREW FORREST: When I found that the U.S.

were threatening countries who were going to vote for the IMO with visa denials, with tariffs, with economic coercion, then I thought, I'm going to sail the Green Pioneer straight into the United Nations General Assembly city for Climate Week and we're going to prove that green shipping is already here.

WILLIAM BRANGHAM: The Green Pioneer, the little ship that can, is now sailing to Brazil for the next United Nations climate conference set to begin next month.

For the "PBS News Hour," I'm William Brangham.