How machines pull pure CO2 straight out of thin air

HostWe talk a lot about how trees breathe in the stuff we don't want in the air. But now we're building these giant metal boxes that try to do the same thing, just way faster. I have been wondering how you even catch something you can't see that's spread so thin through the wind. How do these machines actually grab a specific gas out of the sky?

GuestIt's a huge task because the air is mostly nitrogen and oxygen. If you imagine a big stadium filled with a million balls, only about four hundred of them would be carbon dioxide. To find those few balls, these machines use giant fans to pull the air in. Once the air is inside, it passes over a special material that acts like chemical velcro. This material is designed to only be sticky for that one gas. The rest of the air, the nitrogen and oxygen, just flies right out the back of the machine. But those few bits of carbon dioxide get stuck to the surface of the filter.

HostSo it's like a filter for a furnace, but for one specific kind of gas. But once that filter is full and covered in this gas, what happens? You can't just throw the filter away like you do at home.

GuestNo, you have to get the gas off so you can use the filter again. This is where the real work happens. You close the box so no more air can get in, and then you change the environment inside. Usually, that means turning up the heat to a very high point or using a lot of hot steam. When the material gets hot enough, it loses its grip. It's like the velcro melting a little bit so the gas just falls off. Now you have a pure stream of the gas collected in a tank, and your filter is clean and ready to go back to work catching more from the wind.

HostThat sounds like it would take a massive amount of power. If we're burning gas or coal to get the heat to run a machine that's supposed to help the planet, are we not just making the problem worse while trying to fix it?

GuestThat's the biggest hurdle. If you use dirty power to run these fans and heaters, the math doesn't work out. You might end up putting more carbon into the sky than you pulled out. That's why these plants are usually built in places where there's a lot of clean energy. There's a famous one in Iceland that sits right next to a power plant that gets its energy from the heat of the earth. They use that clean heat to shake the gas loose from the filters. It has to be a closed loop where the energy you use isn't adding to the pile of gas you're trying to shrink.

HostEven if we have the clean power, it feels like a lot of extra steps. Why go through all the trouble of building high tech fans and heaters when a forest does it for free?

GuestTrees are great, but they have limits that machines do not. A tree needs a lot of water and a lot of land, and it takes decades to grow. Plus, when a tree dies or burns in a fire, all that gas it stored goes right back into the air. These machines take up a tiny amount of space compared to a forest. You can put them in the middle of a desert where nothing grows. And once these machines catch the gas, we can put it somewhere it'll never get out. We're not just holding onto it for a few years; we're trying to put it back where it came from.

HostSo where's back? If you have a tank full of this gas, you can't just leave it sitting in a parking lot. Do we just pump it into the ground and hope it stays put?

GuestSome people do pump it into old oil wells, but the coolest way to do it's to turn the gas back into solid rock. In that project in Iceland, they take the gas and mix it with a ton of water, almost like making a very bubbly soda. Then they pump that fizzy water deep into the ground into a type of dark volcanic rock. Because of the minerals in that rock, the fizzy water has a chemical reaction and turns into white veins of stone. It happens pretty fast, too, like within two years. Once it's stone, it's not going anywhere for millions of years.

HostBut this still seems so small compared to how much we pull out of the ground to drive our cars and heat our homes. Is this actually a real fix, or just a very expensive science project?

GuestRight now, it's definitely expensive. It costs hundreds of dollars to pull just one ton of the gas out of the sky. We put out billions of tons every year. So, the scale is the problem. We would need tens of thousands of these giant fan walls all over the world to really move the needle. But the hope is that as we build more, we find cheaper ways to make the sticky chemicals and better ways to use the heat. It's a bit like the first computers or solar panels. They were huge and cost a fortune, and now they're everywhere and cheap.

HostSome people worry that if we get too good at this, we'll just keep burning oil and gas because we think the machines will just clean it up later.

GuestThat's a real worry. This technology should be the last resort for the stuff we can't easily stop, like the fuel for giant planes or making steel. It's much easier to not put the gas in the air in the first place than it's to try and fish it out later with a giant fan. But we have already put so much up there that just stopping now might not be enough. We might need these machines to actually start cleaning up the mess we made over the last hundred years.

HostScientists are even looking at using the captured gas to make things like carbon fiber for bikes or even bubbles for drinks, but the main goal is still getting it back into the earth.

GuestThose giant fans in Iceland are proving that we can actually turn the sky back into stone if we have enough clean heat to power the grab.

HostThe idea of those white veins of stone forming deep underground makes those metal boxes feel a lot more like the trees we were comparing them to at the start.