Despite decades of warnings from climate scientists, the world is still struggling to cut down its CO2 emissions, the main driver of climate change. But a handful of researchers and private companies are trying to fill in some of the gaps with an idea that was once considered fringe: capturing carbon.

In an effort to learn more about how carbon capture works, CBS News' Brook Silva-Braga found himself on the roof of an industrial plant outside Zurich, Switzerland, where rows of circular vents suck carbon dioxide right out of the air.

Louise Charles represents Climeworks, one of a handful of start-ups fighting carbon dioxide by removing it. But to make it a business they needed buyers for the carbon dioxide. They found their first one just a few hundred yards away at a greenhouse looking for fertilizer.

And just down the road from Climeworks, professor Markus Friedl has started using carbon to make fuel. The methane comes out of a gas pump at Rapperswil University of Applied Sciences and into a small fleet of cars. Friedl said the beauty of methane – as opposed to say an electric car – is that the gas is easily stored. An electric battery relying on solar power in the Swiss winter would be hard to charge.

"I'm very convinced that this is part of the solution for climate change," Friedl said.

For that, Climeworks will need more customers, and they got a big one on the day we visited last week: Coca Cola. At a picturesque bottling plant in the Alps, their Swiss carbonated water brand, Valser, became the world's first drink with captured carbon.

Patrick Wittweiler, Coke's sustainability manager in Switzerland, convinced the bosses it was worth paying Climeworks $600 a ton for CO2 that they could get elsewhere for almost nothing.

"Yeah, it's more expensive but to change something and support such a company you have to invest a little bit more," Wittweiler said.

But even all the CO2 in all those bottles is less than a drop in the climate bucket. The Valser plant uses 600 tons of CO2 a year while humanity emits 37 billion tons. And each Climeworks scrubber removes about a ton per week.

But before you dismiss carbon removal – and you wouldn't be alone – consider that intergovernmental climate projections count on some of these methods working.

National Geographic journalist Andrew Revkin has been following the climate story for decades. He's watched as failure to cut emissions forced governments into mathematical contortions to prove it was still possible to hit their CO2 targets and limit warming.

"So this concept emerged of negative emissions. Like something that actually – it's a take-back thing," Revkin said.

According to him, it's the only way to make the math work.

This family of ideas is known as geo-engineering. It could mean carbon removal like Climeworks is doing -- planting millions of trees, which of course consume CO2, or even dumping iron into the ocean to jumpstart it's natural CO2 absorption.

But even if we bring CO2 emissions to zero, temperatures could stay dangerously high for decades.

So Harvard professor David Keith has another idea: Deliberately reflecting away some of the sunlight. We already know volcanic ash does something similar. Spraying aerosols into the stratosphere and reflecting back some sunlight is probably also the cheapest, surest way to lower the global average temperature. There is a catch.

"You don't really care about global average temperature, you care about whether there's a heat wave, or whether your crops have enough water," Keith said.

Keith, who is also involved in carbon removal through his company Carbon Engineering, has spent decades studying what would happen if we dimmed the sun but has run into massive resistance to even the smallest real-world test. Much of the opposition comes from environmentalists.

"People who spent decades trying to fight for emissions cuts are terrified that if we let this topic out in the open that people will use solar geo-engineering as an excuse to keep emitting. They'll say, 'Oh, we've got this problem solved … that's completely wrong," he said.

He thinks its imperative we do both. That's the argument from Climeworks, too, which is trying to dramatically scale up their capacity and bring down their costs. They're working to not only recycle CO2 in soda and fuel, which is carbon-neutral, but at a site in Iceland, actually burying it, making it carbon negative.

Climeworks admits that to scale up to a meaningful size there will have to be a price on CO2 emissions, basically a tax of hundreds of dollars per ton that will make certain things like air travel much more expensive.