Imagine holding a giant sponge, and your job is to soak up as much water as possible. But along the way, some water drips off, some gets absorbed by other things, and some even turns into steam! This is similar to how scientists try to remove carbon dioxide (CO₂) from the air using special kinds of rock powder. These losses and adjustments in carbon dioxide removal efforts show that, just like our sponge, not all of the CO₂ stays where we want it. Losses and adjustments in carbon dioxide removal are inevitable in this process.
Importantly, we can measure these losses to ensure that the final certified CO₂ removal reflects every stage of the removal and storage process.
How do we capture CO₂ with rocks?
To facilitate Enhanced Rock Weathering, farmers spread tiny rock particles over soil, and when these rocks mix with rainwater, a chemical reaction happens. This reaction helps pull CO₂ from the air and store it safely in the soil and water. Like our sponge that loses some water, not all the CO₂ we try to capture actually stays put. These losses and adjustments in carbon dioxide removal are part of the equation. As Dr. Matthew Clarkson, Head of Carbon at InPlanet puts it,
“We have losses due to soil, vegetation, and strong acids. We lose CDR efficiency in the rivers and in the ocean too. But everything else is stored permanently.”
Where does the CO₂ go?
When trying to capture CO₂, some of it gets lost in different ways. Here are the main ones:
Soil and plants take some
• When the rock powder breaks down, it releases important nutrients like calcium and magnesium, known generally as cations.
• These cations must be present to balance against the removed CO2. If the cations are lost, the CO2 is re-released.
• Plants, like sugarcane, love these nutrients and absorb them. But when the plants are harvested and taken away, so too are the cations. As a result some of the CO₂ is lost. As Dr. Junyao Kang, Data Analysis and Modeling Lead at InPlanet explains,
“When we have more sugarcane, and larger sugarcane, then they will also take more cations from the system, causing the Carbon Dioxide Removal (CDR) loss.”
Water carries some away
• Co2 removed in the soils is present as dissolved bicarbonate, which washed down river to the ocean
• On its journey, the bicarbonate molecules may experience changes in their environment. Sometimes the rivers can be more acidic (lower pH) which causes some of our stable bicarbonate to return to the atmosphere
• Once the bicarbonate reaches the ocean another change in the environment occurs, causing more CO2 loss
• What’s left after these losses and adjustments in carbon dioxide removal is permanently stored. We calculate these loss factors based on real data and peer-reviewed research.
Strong acids steal some
• Soil naturally contains different acids. Some of these existing acids come from the use of nitrogen-based fertilizers, which cause acidic soils.
• These acids compete against the carbonic acid in the soil porewater, and can break down the rock powder in ways that don’t store CO₂, meaning some of the captured CO₂ is lost. Dr. Kang described this by sharing that not every part of the rock powder dissolution is driven by CO₂ and that some of it is due to strong acids.
Understanding energy-related emissions
Crushing and transporting the rock powder takes energy, which releases some CO₂ into the air. Scientists subtract these emissions from their total CO₂ removal numbers to make sure they report only the real net impact. According to Dr. Philipp Swoboda, Impact and Science Lead at InPlanet,
“We also had to account for the emissions for our monitoring. So after having everything calculated, we had to measure all the emissions for driving in the field, making the measurements, and conducting analysis.”
How do scientists make adjustments?
To make sure estimates are accurate, scientists measure everything rigorously and carefully. They take soil and water samples, compare different areas, and adjust their results so they don’t overestimate how much CO₂ has actually been removed. These measurements help in understanding losses and adjustments in carbon dioxide removal.
For example:
If they think they captured 1,000 tons of CO₂, but 200 tons were lost to rivers and 100 tons were taken by plants, they will adjust their estimate to 700 tons of CO₂ removal. They also add a little extra caution by using conservative estimates, meaning they assume they captured slightly less than they really did. This helps make sure the results aren’t exaggerated.
“In the long run, 84% of the probability is that we are underestimating our true CDR value,” said Dr. Kang.
Why does this matter?
Carbon removal is super important because it helps fight climate change. But if scientists don’t carefully track what happens to the CO₂, it’s possible to over-estimate removals! That’s why our team spends so much time making sure their calculations are as accurate as possible and accounts for losses and adjustments in carbon dioxide removal.
So, just like making sure our sponge really holds as much water as we think, our team of scientists work hard to make sure carbon removal works the way we expect. And every bit of CO₂ we keep out of the air helps make the planet a better place for everyone.
