The Technosphere: The Hidden Carbon Sink

How human-made products quietly store carbon and impact climate strategies

Time has always been a fascinating concept to me. I still remember hearing about the concept of time travel and “changing” the past of the butterfly effect and thinking for hours about its implications or ways people could use this in their favor.

But it wasn’t just time travel. In school, biology and history were my favorite subjects. Seeing what happened in the past and how that shaped our present realities, I thought, was one of the most fascinating questions in life. It is no wonder that I ended up becoming a paleontologist.

While most have heard of “the carbon cycle” multiple times, when you work in paleontology and climate change science, this is something that you always have in the back of your mind when you present your findings at a conference, when you teach students or read a new research paper.

We know that there’s a limited amount of carbon on earth and that we would rather have it sink to the bottom of the ocean or deep in rock layers than as carbon dioxide in our atmosphere. We talk about ways to naturally sequester this carbon back through plant photosynthesis and other geological processes.

However, I never thought that I had a bling spot about where this carbon was going, or other ways we are requesting it and preventing it from being released to the atmosphere. Or, in other ways, how not all carbon being extracted from sinks is being released into the atmosphere, driving climate change.

I’m talking about the carbon from human-made products.

When we think of carbon and its role in the environment, our minds often go straight to emissions, smokestacks, and climate change. But what if we told you there’s a hidden carbon sink all around us, embedded in the things we use every day?

From the plastics in our gadgets to the asphalt beneath our feet, fossil carbon is quietly stockpiling in the technosphere, a term for the entirety of human-made objects and structures. A recent study in Cell Reports Sustainability highlights just how significant this accumulation is and why it deserves more attention.

As you can imagine, this overlooked carbon storage is rapidly growing, making it a critical topic for understanding our global carbon footprint and its environmental implications.

But let’s look at how they performed this study first.

Researchers turned to a mix of global economic and material data to quantify the fossil carbon stored in durable goods and infrastructure. They focused on 2011, the only year with comprehensive global material flow data, and analyzed carbon flows in and out of various sectors.

Using average carbon content values (e.g., plastics typically contain about 74% fossil carbon), they estimated how much carbon was embedded in products like construction materials, machinery, and consumer goods (yes, like your toothbrush). They then extrapolated their findings to cover 1995 to 2019, offering a long-term perspective on this hidden stockpile.

Ultimately, this approach allowed them to capture the scale of carbon accumulation over decades, emphasizing the need to track these trends as part of climate strategies. See the figure below for a visual explanation of their methods.

And the most important thing: What did they find?

Well, researchers were quite surprised. Between 1995 and 2019, humans added an estimated 8.4 billion tons of fossil carbon to the technosphere.

The thing is that each year, around 400 million tons of this carbon end up in long-lasting products, human-made objects, and constructions that won’t be released into the atmosphere any time soon. To put this into perspective, this is enough to rival the European Union’s annual carbon emissions in 2011.

Construction materials like bitumen, a petroleum-based material that’s primarily used as a binding agent in asphalt pavements, accounted for 34% of this accumulation, with rubber and plastic products contributing 30% and machinery making up 16%.

But here’s the thing: while these products’ carbon is temporarily stored as carbon, this is just a temporary solution, and human-made objects are not requesting new carbon, just preventing it from being released.

Many end up in landfills or as litter, where they take decades or even centuries to degrade. During this period, they’re at risk of being incinerated, releasing carbon back into the atmosphere, or breaking down into microplastics, posing some other environmental challenges.

Interestingly, the study’s authors found that 3.7 billion tons of fossil carbon were disposed of during the study period: 1.2 billion tons ended up in landfills, 1.2 billion tons were incinerated, and 1.1 billion tons were recycled, with the remainder becoming litter. This complex disposal landscape highlights these materials’ dual role as carbon sinks and potential environmental hazards.

On top of that, there’s the fact that these materials were already properly stored in carbon sinks for millions of years before we got them out to make man-made products. So the only silver lightning here is that, once out, they may not contribute as much to carbon emissions as one may think.

But let’s take a step back here. What does this all mean for everyday people, climate activists, and policy-makers?

The study’s authors point out a dual reality: on the one hand, these carbon-rich products can be seen as a “form of sequestration,” especially when they’re confined to stable buildings or landfills for long periods.

On the other hand, without proper waste management, which, let’s be honest, is the most common scenario, they can become environmental hazards. “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,” said Dr. Klaus Hubacek, one of the study’s authors.

This overlooked stockpile grows each year, reminding us of the need to rethink how we manage the lifecycle of durable goods.

I don’t know about you, but I find the idea that human-made materials surpass natural carbon stores extremely shocking and disturbing. It challenges traditional perspectives on carbon management, primarily focusing on emissions and natural sinks like forests and oceans.

This research, however, brings attention to the technosphere, expanding the scope of what we consider part of the carbon cycle. Ultimately, these findings suggest that studies, policies, and practices must evolve to address this underrecognized aspect of carbon storage.

But what’s important here?

There are actionable steps we can take to prevent the potential environmental harm of this hidden carbon sink. Extending the lifespan of products is one way to delay their entry into the waste stream (aka. making them more durable). Improving recycling rates can reduce the demand for virgin fossil carbon. And, of course, policies that focus on minimizing waste discharge from landfills are crucial for limiting environmental harm.

Practical strategies like these mitigate environmental risks and contribute to a circular economy that minimizes waste and maximizes resource use, a necessary step on many fronts.

Ultimately, this research challenges us to expand our understanding of carbon management. It’s not just about reducing emissions but also about managing the materials we create and discard. Doing one without the other will defeat the purpose.

But beyond that, we need to start treating the technosphere as a significant player in the carbon cycle if we want to work towards more sustainable practices that balance human activity with the planet’s needs. Addressing this hidden carbon sink can help us develop innovative solutions to mitigate its impact and integrate it into global climate strategies.

Because knowledge will make us powerful.

Originally published in the Medium Publication The Environment