Investors led by Bill Gates and Kleiner Perkins have poured more than $500 million into carbon-capture tech. Meet the 5 buzziest startups that are turning harmful emissions into fuel and other products.

• To limit global warming to 1.5 degrees and avoid some of the most catastrophic effects of climate change, experts say we have to go beyond reducing emissions and start pulling carbon dioxide directly out of the air. 
• A growing number of startups promise to do that, and they're backed by major VCs including Bill Gates, Khosla Ventures, and Kleiner Perkins, in addition to oil and gas giants like Chevron and ExxonMobil. 
• Companies like Carbon Engineering suck carbon dioxide (CO₂) out of the air and turn it into fuel. Others inject the greenhouse gas into concrete, saving concrete producers money and storing CO₂ indefinitely. 
• Here are the startups garnering the most attention, based on interviews with more than half a dozen investors. 
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Here's the bad news: We've spewed so much carbon dioxide (CO₂) into the air that to limit planetary warming to 1.5 degrees and prevent some of the worse impacts of climate change, we can no longer just limit emissions.

Climate scientists say we need to suck greenhouse gases out of the atmosphere, too.

The good news is that CO₂ isn't just a greenhouse gas. It also has plenty of beneficial uses, like making bubbly sodas, low-emissions fuels, and even helping to strengthen concrete. Once you figure out how to extract it from the air (or from a power plant), you have a near-endless supply. 

"You can either capture CO₂ from a waste stream or use direct air capture technologies and then create a value-add product, whether it's a synthetic fuel, which you can use as jet fuel, or maybe a new polymer," Louis Brasington, an analyst at the research firm Cleantech Group, told Business Insider. 

That's exactly what a trove of new startups is trying to do. Companies like Carbon Engineering and CarbonCure are betting they can turn CO₂ into value — by turning it into fuel or injecting it into concrete.

They're pursuing this technology even absent of a high price on emissions, though these businesses could become even more lucrative if more countries place taxes or limits on emissions.

Some of the world's top clean-energy investors are betting on the tech, too. They include Bill Gates, Kleiner Perkins, and Khosla Ventures, in addition to oil and gas giants like BP, Chevron, and ExxonMobil. In the last two years, they've poured half a billion dollars into carbon capture, storage, and utilization startups, according to PitchBook. 

"If we're going to hit a 2-degree target, and look at the pathways we're on, direct-air capture is very likely going to have to be part of the equation," said Jim Cabot, a managing director at Breakthrough Energy Ventures, a fund spearheaded by Bill Gates. "That would be an area where I expect you're going to see a lot more action in the coming years." 

Here are the top startups where that action is taking place, according to half a dozen investors in the energy industry. They're listed by how much funding they've raised from least to most.

CarbonCure — $11 million

Here's a shocking statistic: If the cement industry was a country, it would be the third-largest greenhouse gas emitter in the world, right behind China and the US, generating 8% of global CO₂ emissions.

And it's not likely to get better anytime soon. According to the International Energy Agency, cement production could increase by as much as 23% in the next 30 years, in response to urbanization and population growth. 

It's in this reality that CarbonCure — a startup that promises to lower emissions in the cement industry — has taken root with a strong coalition of funders. As of 2016, the Canadian company had raised around $11 million, per PitchBook, but it did not disclose the total of its most recent funding round led by Breakthrough Energy Ventures, a fund spearheaded by Bill Gates. 

CarbonCure reduces emissions by sequestering CO₂ in concrete. The company pumps recycled CO₂ into wet concrete while it's being mixed, at which point the gas reacts with water and calcium ions in the cement, forming solid limestone. The carbon is stuck in the limestone indefinitely. What's more, is that this mineralization process makes ready-mix concrete slightly stronger than some alternatives, according to the company. 

CarbonCure technology is installed in nearly 150 concrete plants across North America and Southeast Asia, the company says, and it's used by 100 concrete producers across North America. 

One such producer is the concrete giant Thomas Concrete, which supplied CarbonCure concrete to a new, 42,000 square foot building owned by the Georgia Institute of Technology. The startup says CarbonCure technology saved 40,000 pounds of CO₂ from reaching the atmosphere. 

CarbonCure's founder, Rob Niven, told Business Insider that it's now working on expanding its partnerships and developing new innovations, such as to reduce the use of water.

Climeworks — $34 million

A Swiss-based startup, Climeworks is among the smaller companies selling carbon capture technology, with publicized investment amounting to a little over $30 million. A good chunk of that sum comes from the Zurich Cantonal Bank, the fourth largest bank in Switzerland. 

Climeworks is small, but it's considered a pioneer in the industry. According to reporting by The Washington Post's Steven Mufson, the company — which uses a chemical approach to extract CO₂ from the air — was the first company of its kind to sell CO₂ to a commercial customer.

Among those customers is the Coca-Cola brand Valser, which now sells sparkling water with recycled carbon emissions; a powerplant in Iceland that uses Climeworks technology to capture CO₂ and sequester it in rocks underground through mineralization; and another powerplant in Switzerland, which send the captured emissions to a greenhouse, where it's used as a fertilizer. 

Compared to other carbon capture startups, Climeworks is expensive — it costs about $600 to remove a ton of CO₂ at its plant in Switzerland, as of 2018.

A spokesperson for the company told Business Insider last year that she expects the price to drop to about $200 per ton in the next three or four years. Within the next decade, Climeworks aims to hit its long-term goal of $100 a ton. 

Carbon Engineering — $112 million

Carbon Engineering has raised a little over $110 million to date, per PitchBook, and it's backed by powerful investors including the Bill Gates-led fund, Breakthrough Energy Ventures, and oil and gas giants Chevron, BHP, and Occidental. 

Carbon Engineering pulls CO₂ directly out of the air; its tech is not attached to concentrated emissions sources. Basically, a large fan (or array of fans) pulls in enormous quantities of air and passes it through a chemical solution that reacts with CO₂, sucking the gas out of the air.

The solution, now loaded with carbon, is then mixed with another chemical called calcium oxide to produce pellets of limestone. Finally, those pellets are heated to create what's called quicklime, a substance that, if heated to even higher temperatures, will produce a stream of pure CO₂ that can be used to make synthetic fuel, among other things. 

The startup has a demonstration plant at its headquarters in Squamish, B.C., which captures a meager 1 ton of CO₂ when it's operating, according to the company.

Now, Carbon Engineering is developing its first commercial facility in the Permian Basin in partnership with the oil giant Occidental.

A spokesperson told Business Insider that this new plant, to be completed and operating by 2023, will be able to capture 1 million tons of the greenhouse gas each year. In this case, the captured CO₂ will be pumped into Occidental wells to extract more oil, using an industry practice known as enhanced oil recovery. 

As complicated as Carbon Engineering's process sounds, the company published research in 2018 suggesting its cost-per-ton for capturing CO₂ is $94 to $232, which is far lower than previous estimates for so-called direct-air capture (DAC) technology. It's also lower than the cost estimated by competitors in the industry. 

Solidia Technologies — $118 million

Similar to CarbonCure, Solidia Technology is working to reduce carbon emissions in the cement industry and it's backed by big investors including Kleiner Perkins and BP Ventures. The New Jersey-based startup has a valuation of $261 million, per PitchBook, and it's raised nearly $120 million so far. 

A key step in making cement is heating up a large, rotating kiln filled with limestone and other materials to more than 1,400 degrees. That produces pea-sized clumps of material known as clinker, which are then cooled and ground into a powder. Mix that powder with gravel or sand and water and voila — after it cures, you get hard concrete. 

Within this process, Solidia's technology reduces CO₂ emissions in two ways. First, the startup manipulates the chemistry of the cement ingredients so that the kiln will produce clinker at a lower temperature. Then, instead of using just water to cure the cement, the startup also adds recycled CO₂, which reacts with the cement to form concrete. In other words, Solidia fixes carbon emissions inside the cement. 

The company says it can cut emissions of cement and concrete by up to 70%, while producing a material that is higher-performing and cheaper. 

LanzaTech — $503 million

Since it was founded in 2005, LanzaTech has raised more than half a billion dollars from investors including Khosla, Siemens, and Indian Oil Corporation, making it the largest startup by funding focused on carbon capture and utilization, according to PitchBook. 

LanzaTech turns carbon emissions into ethanol. It captures CO₂ directly from industrial sites, such as steel mills, and then pipes it into a bioreactor filled with carbon-loving microbes. Those microbes eat through the CO₂ and, as a byproduct, produce ethanol — an alcohol that can be sold and blended with gasoline to create fuel. 

The startup is further along than most others in the industry. In May of 2018, it opened its first commercial facility attached to a steel mill in China, which has produced over 10 million gallons of ethanol, according to the company. Later that year, LanzaTech partnered with Virgin Atlantic and Boeing to partially power a commercial flight — from Orlando, FL to Gatwick, England — using jet fuel created with recycled emissions.  

Now, the startup is experimenting with technologies to turn carbon emissions into the building blocks of plastics, polymers, and even Omega-3 fatty acids. The startup is based in Skokie, IL. 

This story is part of Business Insider's energy reporting. Did we miss a company that you think is transforming the carbon capture and utilization industry? Let us know by contacting this reporter at bjones@businessinsider.com.