Construction materials and household items form long-term carbon sink

Construction materials and household items form long-term carbon sink
by Robert Schreiber
Berlin, Germany (SPX) Dec 23, 2024

A significant portion of fossil-derived carbon is stored in human-made products, according to a study published on December 20 in Cell Reports Sustainability. Researchers estimate that approximately 400 million tons of fossil carbon are added annually to durable goods like plastics, buildings, and infrastructure. While these items may act as a "carbon sink," the study emphasizes that effective waste management is critical to prevent these materials from becoming environmental threats.

"We have accumulated more carbon in human-made stuff on the planet than there is carbon in the natural world, but we completely overlook it, and those stocks get bigger and bigger," said Klaus Hubacek, ecological economist and senior author from the University of Groningen. "The message is to look at stocks rather than just flows."

The researchers examined the "technosphere" - all human-made artifacts in use or discarded - by analyzing 2011 data, the only year with comprehensive global material input and output records. They assessed carbon flows into and out of different sectors using the average carbon content of products like plastics, which contain about 74% fossil carbon.

The study revealed that in 2011, 9% of extracted fossil carbon was stored in long-lasting technosphere products. This figure, if emitted as CO2, would nearly equal the European Union's emissions for the same year. Construction materials and infrastructure accounted for the highest accumulation of fossil carbon (34%), followed by rubber and plastic products (30%), bitumen (24%), and machinery (16%).

Expanding their analysis from 1995 to 2019, the researchers estimated that 8.4 billion tons of fossil carbon entered the technosphere during this period, equivalent to 93% of global CO2 emissions in 2019. The annual accumulation of carbon in human-made products increased steadily throughout those years.

Disposal of these materials presents a challenge. Researchers estimate that from 1995 to 2019, 3.7 billion tons of fossil carbon were discarded - 1.2 billion tons went to landfills, 1.2 billion tons were incinerated, 1.1 billion tons were recycled, and the remainder ended up as litter.

"On the one hand, you can consider it as a form of carbon sequestration if this fossil carbon ends up sequestered in landfill, but on the other hand, it poses an environmental hazard, and if you burn it, you increase carbon emissions," said Franco Ruzzenenti, ecological economist and coauthor from the University of Groningen.

The study advocates for extending product lifespans and increasing recycling rates to reduce the amount of fossil carbon entering waste streams. It also calls for stronger policies to limit landfill waste.

Looking ahead, researchers plan to analyze biogenic carbon - carbon derived from plant materials - within durable goods. "For the next step, we plan to investigate the long-term potential of biogenic carbon sequestration in durables," said first author Kaan Hidiroglu. "This will allow us to assess whether diversifying carbon sequestration strategies, such as relying on biogenic carbon in durables such as wood materials for construction, could be a viable option."

Research Report:The Extent and Fate of Fossil Carbon Accumulation in our Technosphere