Heat trapping carbon dioxide emissions from making cement, a less talked about but major source of carbon pollution, have doubled in the last 20 years, new global data shows.
In 2021, worldwide emissions from making cement for buildings, roads and other infrastructure hit nearly 2.9 billion tonnes of carbon dioxide, which is more than 7 per cent of the global carbon emissions, according to emissions scientist Robbie Andrew of Norway’s CICERO Center for International Climate Research and the Global Carbon Project. Twenty years ago, in 2002, cement emissions were about 1.4 billion tonnes of carbon dioxide.
Driven by China, global cement emissions globally have more than tripled since 1992, recently growing at a rate of 2.6 per cent a year. It’s not just that more cement is being made and used. At a time when all industries are supposed to be cleaning up their processes, cement has actually been going in the opposite direction. The carbon intensity of cement – how much pollution is emitted per tonne – has increased 9.3 per cent from 2015 to 2020, primarily because of China, according to the International Energy Agency.
“Cement emission have grown faster than most other carbon sources,” said Stanford University climate scientist Rob Jackson, who leads Global Carbon Project, a group of scientists that track worldwide climate pollution and publish their work in peer reviewed journals.
“Cement emissions were also unusual in that they never dropped during COVID-19. They didn’t grow as much, but they never declined the way oil, gas and coal did. Honestly, I think it’s because the Chinese economy never really shut down completely.”
Cement is unusual compared to other major materials, such as steel, because not only does it require a lot of heat to make, which causes emissions, but the chemical process of making cement itself produces a lot of carbon dioxide, the major human-caused long-term heat-trapping gas.
The recipe for cement requires lots of a key ingredient called clinker, the crumbly binding agent in the entire mixture. Clinker is made when limestone, calcium carbonate, is taken out of the ground and heated to 1,480 to 1,540 degrees Celsius to turn it into calcium oxide. But that process strips carbon dioxide out of the limestone and it goes into the air, Andrew said.
Rick Bohan, senior vice president for sustainability at the industry group Portland Cement Association, said, “in the US, 60 per cent of our CO2 is a chemical fact of life … The reality is concrete is a universal building material. There is no single construction project that doesn’t use some amount of concrete in it.”
Cement, which is the key ingredient in concrete, is in buildings, roads and bridges.
“Each person on the planet is consuming on average more than a kilogramme of cement per day,” said University of California Earth systems scientist Steve Davis. “Obviously, you’re not going to, you know, Home Depot and buying a sack of cement every day. But on your behalf, the roads and buildings and bridges out there are using more than a kilogramme. And that’s kind of mind boggling to me.”
Even though there are greener ways to make cement, cutting its emissions dramatically is so difficult and requires such a massive change in infrastructure and the way of doing business, the International Energy Agency doesn’t envision the cement industry getting to zero carbon emissions by 2050. Instead there will still be emissions from cement, steel and aviation that need to be balanced out with negative emissions elsewhere, said IEA researchers Tiffany Voss and Peter Levi.
“These are hard, hard to cut,” Andrew said.