The cement industry is a big emitter of carbon dioxide, making up about 7% of emissions globally. There’s interest in changing that, including from the industry itself.

Two major producers of cement, Holcim and CRH, are backing a startup called Sublime Systems, the company announced Tuesday. It’s developed an alternative way of creating cement that generates fewer emissions than the traditional process.

Cement is traditionally made primarily from limestone. It’s heated up in kilns to around 2,732 degrees Fahrenheit.

So hot, electricity won’t really get the job done, said Jeremy Gregory, who leads the Massachusetts Institute of Technology’s Climate and Sustainability Consortium. 

“We pretty much have to use fossil fuels now, either coal or natural gas,” Gregory said.

Gregory, who also counts Holcim as a backer of his research at MIT, said that’s one reason cement-making is carbon intensive. Another is that limestone emits carbon as it’s heated up.

Cement is a key ingredient — basically the glue — in concrete, which we use a lot of.

“Concrete is the most-used substance on Earth besides water,” Gregory said.

There are ways to make cement with less carbon, including using biomass instead of fossil fuels to heat up the kilns. 

Also, companies are making cement blends that include alternatives to limestone.

There’s also a push to capture the carbon that’s being emitted at cement plants, said Paul Adeleke with the Global Cement and Concrete Association.

But, he said, decarbonization does come at a price. 

“It would add about 5% onto the cost of a typical house, being able to deliver sort of net zero cement and concrete,” Adeleke said.

Another possibility? Use less concrete as we build cities, said Jay Koh of the Lightsmith Group, a climate-focused private equity firm. 

“If you converted areas back into parkland or greenery, then that has a much more absorptive capacity for flood events or for rain events that are increasingly happening,” Koh said.

Essentially, less gray infrastructure and more green.