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Over the past 20 years, cement manufacturers have quietly doubled their carbon dioxide emissions, highlighting a sector that has received relatively little public scrutiny despite contributing nearly three times as much to global warming as the airline industry. With cement production only expected to increase through mid-century, a growing number of people are now calling for a more concerted effort to tackle concrete’s expanding carbon footprint.

Scientists say that the cement industry will need to decrease its annual emissions by at least 16 percent by 2030 to be in line with the Paris Agreement. But between 2002 and 2021, the industry’s global emissions doubled from 1.4 billion tons of carbon dioxide to nearly 2.9 billion tons, according to data from the CICERO Center for International Climate Research and the Global Carbon Project that was shared with the Associated Press. 

Cement manufacturing now accounts for at least 8 percent of all the world’s CO2 emissions. In comparison, aviation accounts for about 2.8 percent of total global emissions, according to a 2020 report from the International Energy Agency.

“Cement emissions have grown faster than most other carbon sources,” Rob Jackson, a climate scientist at Stanford University who leads the Global Carbon Project, told the AP, adding that the climbing emissions can largely be tied to increased manufacturing in China.

Used to build much of the infrastructure that enables today’s modern society—think roads, bridges, buildings and even the ground you walk on—concrete is the second-most widely used substance on Earth, behind only water. And according to the IEA, the cement sector is the third-largest consumer of energy and the second-largest emitter of carbon dioxide when looking at industrial players alone.

Making cement is by its nature a highly energy-intensive process. Raw materials like clay and limestone are heated to more than 2,500 degrees Fahrenheit to turn them into a binding agent for sand, gravel or other coarse materials. But unlike other major construction commodities, concrete produces carbon emissions in two ways, not just one. 

Manufacturing steel, for example, produces greenhouse gas emissions because running the steel plants requires energy, and that electricity and heat still overwhelmingly comes from burning fossil fuels. Manufacturing concrete similarly requires power, but the chemical process of making cement itself also produces significant amounts of carbon dioxide. Altogether, roughly 1,370 pounds of CO2 is produced for every metric ton of cement manufactured, researchers say.

That makes the cement industry especially difficult when it comes to reducing its climate impact. But a growing movement, led by researchers and environmental activists, is pushing the industry and government regulators to do just that. At least two states, New York and California, have recently passed laws that aim to reduce greenhouse gas emissions from the cement industry.

Last year, California became the first state in the nation to require mandatory emissions reductions from cement manufacturing. Under that new law, the carbon emissions per ton of cement produced in the state must be cut by 40 percent below 2019 levels by 2035. New York also passed a law in 2021, albeit a much narrower one. Under New York’s legislation, the state is required to set an emissions standard for concrete used in public works. 

In May, more than 50 corporations pledged at an international economic summit to begin purchasing “low-carbon” versions of cement, steel, aluminum and other major construction commodities that typically have a high carbon footprint. Among the companies that made the pledge were tech giants Microsoft, Google and Salesforce.

“We are creating a demand for low-carbon products,” particularly for nascent clean technologies in steel, aviation, aluminum, cement and chemicals, Borge Brende, president of the World Economic Forum, told the New York Times.

Such commitments are galvanizing the race to find new ways to produce more climate-friendly cement. Last year, a pair of researchers from the University of Tokyo, for example, discovered a way to reduce the carbon emissions of concrete by making it out of food scraps.

But the search for greener cement has also led to trends that are making many climate activists nervous. In some cases, the surge of interest and funding going into making the industry less carbon-intensive has led policymakers to look to controversial technologies like carbon capture and storage as a way to bring down the cement sector’s footprint.

California, for example, is heavily relying on nascent and unproven carbon removal technologies to achieve much of the state’s mandatory emissions reduction targets for several industrial sectors, including cement manufacturing. Many environmentalists have long objected to carbon removal technologies, saying they are expensive, difficult to scale and distract from proven solutions like switching to renewable energy sources like solar and wind.

“Carbon capture and storage is pitched as one simple trick that can solve the genuine challenge of hard-to-abate emissions, but it may actually make the climate problem worse,” Steven Feit, an attorney at the Center for International Environmental Law, told California lawmakers at a recent public hearing. “It will be a lifeline for emitting facilities and will lock in fossil fuels for decades to come.” 

That’s it this week for Today’s Climate. Thanks for reading, and I’ll be back in your inboxes on Tuesday.

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