Emissions of carbon dioxide trapped by heat from cement production, a less talked about but significant source of carbon pollution, have doubled in the last 20 years, according to new global data.
In 2021, global emissions from cement production for buildings, roads and other infrastructure hit nearly 2.9 billion tonnes (2.6 billion metric tonnes) of carbon dioxide, which is more than 7% of global carbon emissions, according to Norway’s emission scientist Robbie Andrew. CICERO Center for International Climate Research and the Global Carbon Project. Twenty years ago, in 2002, cement emissions were about 1.4 billion tonnes (1.2 billion metric tonnes) of carbon dioxide.
China-led global cement emissions have more than tripled since 1992, recently rising at a rate of 2.6% per year. It is not just that more cement is made and used. At a time when all industries are supposed to clean up their processes, cement is actually moving in the opposite direction. Cement carbon intensity – how much pollution is emitted per tonne – has increased by 9.3% from 2015 to 2020, mainly due to China, according to the International Energy Agency.
“Cement emissions are rising faster than most other carbon sources,” said Rob Jackson, a climate scientist at Stanford University who leads the Global Carbon Project, a team of scientists monitoring global climate pollution and publishing with judges. “Cement emissions were also unusual as they never fell during COVID. They did not grow as much, but they never declined like oil, gas and coal. “Honestly, I think it’s because the Chinese economy has never closed completely.”
Cement is unusual compared to other main materials, such as steel, because not only does it require a lot of heat to build, which causes emissions, but the chemical process of cement production itself produces a lot of carbon dioxide, the main anthropogenic long-term trapping gas. heat.
The cement recipe requires a lot of a key ingredient called clinker, the brittle binder in the whole mix. Clinker is made when limestone, calcium carbonate, is removed from the soil and heated to 2700 to 2800 degrees (1480 to 1540 degrees Celsius) to be converted to calcium oxide. But that process removes carbon dioxide from the limestone and goes into the air, Andrew said.
Rick Bohan, senior vice president of sustainability at the Portland Cement Association, said, “In the United States, 60% of our CO2 is a chemical fact of life … The reality is that concrete is a universal building material. “There is no construction project that does not use any amount of concrete in it.”
Cement, which is the main component of concrete, is found in buildings, roads and bridges.
“Every person on the planet consumes an average of more than a pound (2.2 pounds) of cement a day,” said Steve Davis, a University of California’s Earth systems scientist. “Obviously, you’re not going to, you know, Home Depot and buy a bag of cement every day. But on your behalf, the roads, buildings and bridges out there use more than a pound. And that confuses me. “
Although there are greener ways to produce cement, dramatically reducing its emissions is so difficult and requires such a massive change in infrastructure and business, the International Energy Agency does not predict that the cement industry will have zero carbon emissions by 2050. Instead, there will still be emissions from cement, steel and aviation that need to be offset by negative emissions elsewhere, said IEA researchers Tiffany Voss and Peter Levi.
“These are difficult, difficult to cut,” Andrew said.
However, industry Bohan said his team is confident it can reach zero carbon emissions by 2050 if it receives help from governments and especially cement users to accept and use green cement properly. One of the various ways to make greener cement is to mix it with fly ash, which is a waste of coal burning, in place of a clinker, and said there is more than enough fly ash available even with reduced carbon usage.
The IEA Voss said the transition to green cement “does not yet exist” due to technology, infrastructure and other concerns. But many inside and outside the industry are working on the problem.
China is the key because it produced more than half of the world’s cement emissions in 2021, with India second with about 9%, according to Andrew. The United States released 2.5% of its emissions from cement, ranking fifth behind Vietnam and Turkey.
“China is a huge country and its growth has accelerated,” Andrew said. “It drives everything.”
China does not just produce and use more cement, but coal intensity has risen sharply in recent years, the IEA’s Voss said. This is because earlier in its development, China used cheaper, weaker low-clinker cement and buildings and bridges collapsed, so now the Chinese government is imposing stronger cement, said Andrew of Norway.
“This is a reasonable conservatism that is slowing down efforts to produce greener cement,” Davis said. “People are not willing to try untested cement recipes because” these are the building blocks of our society, “he said.
For example, Portland limestone cement has 10% less emissions, but customers are so concerned about durability that they often say they are only willing to use it if they use 10% more, said Bohan of the industry.
Different uses of cement have specific needs, such as longevity, but users often just want the strongest and most durable when they do not need it, and this causes unnecessary emissions, Bohan said.
And while people are talking about restricted flights, global aviation emissions are less than half that of concrete, according to the Global Carbon Project. There is “flight embarrassment” between scientists and activists, but not building, Davis said.
As cement ages, it absorbs some carbon dioxide from the air, just like trees, in small, measurable quantities, Jackson said.
“Our main focus should be on the use of fossil fuels because that’s where most emissions come from,” said Stanford-based Jackson. “I do not think cement is on the radar of most politicians.”
Maybe not in most, but it is in some. California, Colorado, New Jersey and New York have all passed legislation for cleaner concrete, and the trend is growing.
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