We have a good understanding of how much carbon from fossil fuels is released into the atmosphere, but we’re less informed about the amount that is stored in products created by humans. According to ecological economists, around 400 million tons of fossil carbon are added annually to durable items like plastics, buildings, and infrastructure. While these items might function as a ‘carbon sink,’ effective waste management is crucial to ensure they do not become environmental threats.
We have solid insights on the carbon emissions from fossil sources, but our knowledge about the carbon captured in human-made products is still limited. A recent study published on December 20 in the journal Cell Reports Sustainability by ecological economists reveals that humans contribute approximately 400 million tons of fossil carbon each year to long-lasting materials, including plastics and buildings. These materials can act as a “carbon sink,” but appropriate waste management is vital to keep them from becoming environmental dangers.
“We have gathered more carbon in human-made products than what exists in nature, yet we often overlook this, and the amount continues to rise,” explains Klaus Hubacek, an ecological economist and senior author from the University of Groningen. “The key takeaway is to focus on stocks instead of merely flows.”
The true extent of fossil carbon stored in what is termed the “technosphere”—the collection of all human-created objects, whether in use or discarded—is poorly understood. To gauge these stocks and track changes yearly, researchers used publicly accessible data on material inputs and outputs across various economic sectors globally for the year 2011, which is the only year with such comprehensive data available globally.
Following this, they calculated the carbon inflow and outflow for different sectors by analyzing the average carbon content of various products (for instance, plastics typically consist of about 74% fossil carbon). The study took into account not only end products like durable plastics and bitumen but also fossil carbon sources used as intermediate materials in various industries.
The researchers discovered that in 2011, 9% of the fossil carbon extracted was stored in enduring products within the technosphere. If this quantity of carbon had been released as CO2, it would be nearly equivalent to the EU’s emissions that year (3.7 Gt of accumulated carbon versus 3.8 Gt released). The creation of buildings and infrastructure contributed the most to the accumulation of fossil carbon (34%). When analyzing product categories, rubber and plastic contributed 30% of the stored fossil carbon, followed by bitumen (24%; used in roofing and roads), and machinery and equipment (16%).
Subsequently, the research team projected their 2011 findings to estimate the flow of fossil carbon into the technosphere from 1995 to 2019, utilizing monetary data from that timeframe. Overall, they approximated that 8.4 billion tons of fossil carbon were added during those years, which is about 93% of the global CO2 emissions in 2019. The annual influx of carbon into the technosphere grew every year from 1995 to 2019.
A large portion of these fossil carbon products either end up in landfills or become litter, taking many decades to even centuries to decompose. Based on the average lifespan of buildings, infrastructure, and other products, researchers estimate that 3.7 billion tons of fossil carbon were disposed of in that period—1.2 billion tons went to landfills, another 1.2 billion tons were incinerated, 1.1 billion tons were recycled, and the rest became litter.
“On one hand, it’s viewed as a method of carbon sequestration when fossil carbon is relegated to landfills, but on the flip side, it can cause environmental issues. Furthermore, burning it raises carbon emissions,” notes Franco Ruzzenenti, co-author and ecological economist from the University of Groningen.
To mitigate the volume of fossil carbon in waste systems, the researchers suggest enhancing the lifespan of products and improving recycling rates. They also highlight the necessity of implementing policies that restrict the overflow of waste from landfills.
Looking forward, the team intends to carry out a similar study focusing on biogenic carbon, which derives from plant materials.
“For our next project, we aim to explore the long-term prospects of biogenic carbon capture in durable goods,” states Kaan Hidiroglu, the first author from the University of Groningen. “This research will help us evaluate whether diversifying carbon capture methods, like using biogenic carbon in durable materials such as wood for construction, could be a feasible solution.”
