Carbon dioxide emissions from cement are quietly doubling in 20 years

Carbon dioxide emissions from cement are quietly doubling in 20 years

Heat-trapping carbon dioxide emissions from cement manufacture, a less discussed but major source of carbon pollution, have doubled over the past 20 years, new global data shows.

In 2021, global emissions from the manufacture of cement for buildings, roads and other infrastructure reached nearly 2.9 billion metric tons (2.6 billion metric tons) of carbon dioxide, equivalent to more than 7% of global carbon emissions, according to emissions scientist Robbie Andrew of Norway CICERO Center for International Climate Research and the Global Carbon Project. Twenty years ago, in 2002, cement emissions were about 1.4 billion tons (1.2 billion metric tons) of carbon dioxide.

Driven by China, global cement emissions have more than tripled since 1992 and have recently risen by 2.6% per year. Not only is more cement being made and used. At a time when all industries should clean up their processes, cement is actually going in the opposite direction. According to the International Energy Agency, the carbon intensity of cement – how much pollutants are emitted per tonne – increased by 9.3% from 2015 to 2020, mainly because of China.

“Cement emissions have been growing faster than most other carbon sources,” said Stanford University climate scientist Rob Jackson, who leads the Global Carbon Project, a group of scientists that tracks global climate pollution and publishes their work in peer-reviewed journals. “Cement emissions have also been unusual in that they have never fallen during COVID. They didn’t grow as much, but they never declined like oil, gas, and coal. To be honest, I think it’s because the Chinese economy has never really shut down completely.”

Cement is unusual compared to other key materials such as steel because not only does it require a lot of heat to produce, causing emissions, but the chemical process of making cement itself produces a lot of carbon dioxide, the main man-made long-term heat storage gas.

Cement’s formulation requires a lot of a key ingredient called clinker, the crumbly binder throughout the mix. Clinker is formed when limestone, calcium carbonate, is taken from the ground and heated to 2700 to 2800 degrees (1480 to 1540 degrees Celsius) to turn it into calcium oxide. But that process removes carbon dioxide from the limestone and it becomes airborne, Andrew said.

Rick Bohan, senior vice president of sustainability at industry group Portland Cement Association, said, “In the US, 60% of our CO2 is a chemical fact of life… The fact is, concrete is a universal building material. There isn’t a single construction project that doesn’t use a certain amount of concrete.”

Cement, the main component of concrete, is found in buildings, roads and bridges.

“Every person on Earth uses an average of more than a kilogram of cement per day,” said University of California Earth system scientist Steve Davis. “Obviously you’re not going to, you know, buy Home Depot and buy a bag of cement every day. But on your behalf, the roads and buildings and bridges out there consume more than a kilogram. And that’s kind of amazing to me.”

Although there are greener ways to make cement, drastically reducing its emissions is so difficult and requires such a massive change in infrastructure and ways of doing business that the International Energy Agency does not expect the cement industry to reach zero carbon emissions by 2050. Instead, it will there are still emissions from cement, steel and aviation that need to be offset with negative emissions elsewhere, said IEA researchers Tiffany Voss and Peter Levi.

“They’re tough, hard to cut,” Andrew said.

But the industry’s Bohan said his group is confident it can achieve net-zero carbon emissions by 2050 if it has the support of governments, and especially cement users, to embrace and use green cement properly. One of several ways to make greener cement is to mix in fly ash, a waste product from burning coal, in place of some of the clinker, and he said that even with reduced coal use, there was more than enough fly ash available.

The IEA’s Voss said the move to green cement “isn’t there yet” due to technology, infrastructure and other concerns. But many inside and outside the industry are working on the problem.

China plays a key role as it accounted for more than half of global cement emissions in 2021, while India is a distant second at about 9%, Andrews data shows. The United States caused 2.5% of emissions from cement, ranking fifth behind Vietnam and Turkey.

“China is a huge country and its development has increased greatly,” Andrew said. “It drove everything.”

Not only is China producing and using more cement, but carbon intensity has risen sharply recently, the IEA’s Voss said. That’s because China used cheaper, weaker, low-clinker cement earlier in its development and buildings and bridges collapsed, so the Chinese government is now mandating stronger cement, said Andrew from Norway.

That’s sensible conservatism that’s slowing efforts to make greener cement, Davis said. People aren’t keen on trying untested cement recipes because “these are the structural materials of our society,” he said.

For example, Portland limestone cement has 10% fewer emissions, but customers are so concerned about strength that they often say they would only use it if they use 10% more, said the industry’s Bohan.

Different cement applications have specific requirements, such as B. Strength versus durability, but users often just want the strongest and most durable when they don’t need it, and that creates unnecessary emissions, Bohan said.

And while people are talking about cutting down on flying, less than half of the world’s emissions from aviation come from concrete, according to the Global Carbon Project. There is “flight shaming” among scientists and activists, but no building shaming, Davis said.

Cement absorbs some carbon dioxide from the air as it ages, just like trees do, in small, measurable, significant amounts, Jackson said.

“Our primary focus needs to be on the use of fossil fuels because that’s where most of the emissions come from,” Stanford’s Jackson said. “I don’t think cement is on the radar of most policymakers.”

Maybe not for most, but for some it is. California, Colorado, New Jersey, and New York have all passed cleaner concrete laws, and the trend is growing.


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