Now, he's focusing on climate change, agreeing with the overwhelming majority of scientists who warn of a looming climate disaster.

The good news is Gates believes it's possible to prevent a catastrophic rise in temperatures.

The bad news?

He says in the next 30 years, we need scientific breakthroughs, technological innovations, and global cooperation on a scale the world has never seen.

The story will continue in a moment.

You believe this is the toughest challenge humanity has ever faced?

Absolutely.

The amount of change, new ideas, it's way greater than the pandemic.

And it needs a level of cooperation that would be unprecedented.

That doesn't sound feasible.

No, it's not easy.

It sounds impossible.

But hey, we have 30 years.

We have more educated people than ever.

We have a generation that's speaking out on this topic.

And, you know, I got to participate in the miracle of the personal computer and the Internet.

And so, yes, I have a bias to believe innovation can do these things.

He's talking about innovations in every aspect of modern life, manufacturing, agriculture, transportation, because nearly everything we now do releases earth-warming greenhouse gases, mainly carbon dioxide, into the atmosphere.

He took us to his favorite burger joint in Seattle to explain.

You're talking about changing everything in the economy, I mean, every aspect of it.

Yeah, the physical economy.

So, of what we can see right now, of us sitting around here, what specifically would be impacted?

Well, this cement would be made in a different way.

The steel in the building would be different.

You know, the meat in the burger is a big deal.

These, you know, all this plastic and paper, potatoes.

With potatoes, you're talking about fertilizer, the irrigation system that's used.

All the tractors, the transport.

Or trucks that bring them to this restaurant.

All that has to change.

Hey, when you're going to zero, you don't get to skip anything.

Gates says going to zero means eliminating all greenhouse gas emissions or else.

If they wait 100 years to do this.

It's way too late.

Then the natural ecosystems will have failed.

The instability, you know, the migration.

Those things will get really, really bad well before the end of the century.

When you're talking about migration, you're talking about hundreds of thousands of people trying to move from North Africa to Europe every year.

Exactly.

The Syrian war was a 20th of what climate migration will look like.

So the deaths per year are way 10 times greater than what we've experienced in the pandemic.

In a new book, How to Avoid a Climate Disaster, Gates outlines all the solutions he believes we need.

He says the U.S. has to lead the world getting to zero greenhouse gas emissions by 2050.

He supports President Biden's decision to rejoin the Paris climate agreement, but is asking the administration to massively increase the budget for climate and clean energy research to $35 billion a year.

You've said that governments need to do the hard stuff, but not just go after the low hanging fruit.

What's the low hanging fruit?

Passenger cars, part of the electric generation with renewables.

The things everybody knows about, that's getting almost all the money, not the hard parts, which is the industrial piece, including the steel and cement.

Those pieces we've hardly started to work on.

No one thinks much about cement and steel, but making it accounts for 16 percent of all carbon dioxide emissions, and the demand is only growing.

The world will add an estimated 2.5 trillion square feet of buildings by 2060.

That's the equivalent of putting up another New York City every month for the next 40 years.

So one innovative company Gates has been pouring money into is CarbonCure.

They inject captured carbon dioxide into concrete.

What they do is they stick CO2 in here, in the cement, and they mix them up.

And so you're able to actually get rid of some CO2 by sticking it in the cement.

Right now they get rid of about 5 percent, but they have a next generation they can get to 30 percent.

The carbon has been just injected into this, so it's captured it, so it's not going to be released into the atmosphere.

That's right.

Gates has already invested $2 billion of his own money on new green technologies and plans to spend several billion more.

In 2016, he also recruited Jeff Bezos, Mike Bloomberg and nearly two dozen other wealthy investors to back a billion-dollar fund called Breakthrough Energy Ventures, making long-term, often risky, investments in promising technologies.

It kind of blows my mind, you know, what's the cost of making that stuff?

Gates regularly consults with the fund's team of top scientists and entrepreneurs who've so far invested in 50 companies with cutting-edge ideas to reduce carbon emissions.

What's like the most far-flung idea you've backed?

There's one that's so crazy it's even hard to describe.

Wait a minute.

It's so crazy it's hard to describe.

How do you pitch that to investors?

They find geological formations and they just pump water down into them.

The energy they've used to pump it in, then they can draw that energy back out.

So it's a water pressure storage thing, which, you know, when I first saw it, I thought, that can't work.

But...

But you gave money to it?

Yeah, lots of money.

Because cows account for around 4 percent of all greenhouse gases, Gates has invested in two companies making plant-based meat substitutes, Impossible Foods and Beyond Meat.

But farming the vegetables used to make many meat alternatives emits gases as well.

So Gates is also backing a company that's created an entirely new food source.

This company Nature Find is using fungi and then they turn them into sausage and yogurt.

Pretty amazing.

When you say fungi, do you mean like a mushroom or a microbe?

It's a microbe.

The microbe was discovered in the ground in a geyser in Yellowstone National Park.

Without soil or fertilizer, it can be grown to produce this nutritional protein that can then be turned into a variety of foods with a small carbon footprint.

This is the yogurt.

Oh, this is good.

Wow.

I've had like cashew yogurt or oat yogurt.

It's sort of along those lines.

Yeah, with the burgers, they're, you know, like beyond impossible.

They're getting close to the real thing, but you can still tell.

These I'm not sure I could have...

I'm more of a burger expert than I am a yogurt expert.

Gates never planned to focus on climate change.

But while working in Africa with the foundation he started with his wife Melinda in 2000, he came to see just how vulnerable those in developing countries are to the effects of rising temperatures.

So 15 years ago, Gates started educating himself on climate change, bringing scientists and engineers to his office in Seattle for what he calls learning sessions.

He also reads voraciously books and binders full of scientific research.

Yeah, so this is the most recent one, which is about clean hydrogen.

So you're reading thousands of pages every few days on topics.

Yeah, my reading is key and then asking questions when it doesn't make sense.

Gates isn't just looking to cut future carbon emissions.

He's also investing in direct air capture, an experimental process to remove existing CO2 from the atmosphere.

Some companies are now using these giant fans to capture CO2 directly out of the air.

Gates has become one of the world's largest funders of this kind of technology.

But of all his green investments, Gates has spent the most time and money pursuing a breakthrough in nuclear energy, arguing it's key to a zero carbon future.

He says he's a big believer in wind and solar and thinks it can one day provide up to 80 percent of the country's electricity.

But Gates insists unless we discover an effective way to store and ship wind and solar energy, nuclear power will likely have to do the rest.

Energy from nuclear plants can be stored so it's available when the sun isn't shining and the wind isn't blowing.

Were you always a big proponent of nuclear?

In 2008, he founded TerraPower, a company that has redesigned a nuclear reactor.

This is your prototype?

Exactly.

TerraPower's naturing reactor.

This is a rendering.

We haven't built it yet.

But here's the nuclear island right here.

This is the reactor? Gates says TerraPower's reactor is less expensive to build, produces less waste, and is fully automated, reducing the potential for human error.

Gates and Director of Engineering Lindsay Bowles showed us what they say is another key to its safety.

What is it that we're looking at here?

So these individual fuel pins are actually where the uranium fuel is, and that's what generates all the heat in our natrium reactor.

This is what everybody is worried about?

Yes, exactly.

In a normal reactor, it's water that's flowing past and heating up.

And it'll boil and generate a lot of high pressure.

That high heat and pressure can cause an explosion, like in Chernobyl in 1986, when radioactive material was spread for thousands of miles.

But Gates says the TerraPower reactor won't use water to cool down the fuel rods.

They plan to use liquid sodium.

The liquid sodium can absorb a lot more heat, and so we don't have any high pressure inside the reactor.

In October, the Department of Energy awarded TerraPower $80 million to build one of the first advanced nuclear reactors in the U.S.

Nuclear power can be done in a way that none of those failures of the past would recur, because just the physics of how it's built.

I admit, convincing people of that will be almost as hard as actually building it.

But since it may be necessary to avoid climate change, we shouldn't give up.

You've been criticized for being a technocrat, saying technology is the only solution for tackling climate change.

There are other people who say, look, the solutions are already there.

It's just government policy is what really needs to be focused on.

I wish that was true.

I wish all this funding of these companies wasn't necessary at all.

Without innovation, we will not solve climate change.

We won't even come close.

Gates credits young activists for keeping climate change in the headlines, but he knows some consider him an imperfect ally.

Are you the right messenger on this?

Because you fly private planes a lot and you're creating a lot of greenhouse gases yourself.

Yeah, I probably have one of the highest greenhouse gas footprints of anyone on the planet.

You know, my personal flying alone is gigantic.

Now I'm spending quite a bit to buy aviation fuel that was made with plants.

You know, I switched to an electric car.

I've used solar panels.

I'm paying a company that actually at a very high price can pull a bit of carbon out of the air and stick it underground.

And so I'm offsetting my personal emissions.

Those are called carbon offset.

Right.

So, you know, it's costing like four hundred dollars a ton.

It's like seven million dollars.

So you're paying seven million dollars a year to offset your carbon footprint.

Yep.

He's encouraging others who can afford it to buy carbon offsets and green products so that what he calls the green premium, the added production costs for reducing carbon emissions will go down and quality of products up, driving the innovations that may get us to zero.

It just seems overwhelming if every aspect of our daily life has to change.

It can seem overwhelming.

But you are optimistic.

Yeah.

There are days when it looks very hard.

If people think it's easy, they're wrong.

If people think it's impossible, they're wrong.

It's possible.

It's possible.

But it'll be the most amazing thing mankind has ever done.

That's what it has to be.

Yeah.

It's an all out effort, you know, like a world war.

But it's us against greenhouse gases.

Bill Gates' advice on how to combat mistrust in science at 60minutesovertime.com.

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