Negative Emissions 101: An Introduction
What are negative emissions?
“Negative Emissions” is a term used to describe the process of taking carbon out of the atmosphere and then using or storing it in some kind of way. “Negative” is thereby nothing bad but describes the fact that we subtract from the atmosphere, rather than to add to it.
Clarification on Carbon positive, neutral and negative
Positive:
- You go to a forest and burn a tree. That is carbon positive since it releases more carbon into the atmosphere than it withdraws.
Neutral:
- You plant a tree, and it sequesters 1 ton in its biomass and the surrounding soil. You burn the tree, and all sequestered carbon is released. That is carbon neutral since the amount of carbon taken from the atmosphere and put into the atmosphere are equal.
Negative:
- You plant a tree, and it sequesters 1 ton from the atmosphere, and you do not burn it. That is carbon negative since it removes more carbon from the atmosphere than it emits.
- You plant a tree, and it sequesters 1 ton from the atmosphere. You log it and use the wood as building material. That is carbon negative since when using wood as a building material, the carbon stored in the biomass is not released.
Why do we need them?
Carbon is generally nothing bad. In fact, 18% of your body is carbon, and carbon is referred to as “the building block of life”. So the problem is not the amount of carbon there is on our planet, it is the position or balance of this carbon.
Preferably, we want a balance that allows the ecosystems to be in good health, that our life is dependent on. At the moment, the amount of carbon and other greenhouse gases in our atmosphere is too high, which lead to the climate crisis and puts our living conditions at risk. Although the amount of carbon in the atmosphere and the industrial emissions (as seen in the figure) might appear to be fairly small, they pose an existential threat. The atmosphere is really nothing to mess with. In fact, all five mass extinctions we know about were related to atmospheric composition or the climate.
Over the last centuries (and also now), we paid companies to extract carbon-rich substances like coal, oil or gas from the ground, so we could burn them to make our machines go. These companies became very rich, powerful and good at extracting carbon-rich substances from the ground. Our society undoubtedly benefited enormously from the benefits of a fossil-fueled economy. Unfortunately, that has thrown us “a bit” off-balance, in terms of carbon. As the graph indicates. To make it even worse, 1Kg of Oil does not result in 1Kg of CO2 but in 3Kg. (see here for detailed list).
What is their role in comprehensive climate-action?
So we learned: to mitigate the effects of the climate crisis, we need to reduce the amount of carbon in the atmosphere. And there are two ways to do that:
- Avoid new carbon getting into the atmosphere (in terms of our newly learned slang, that would be “reduce positive emission”)
- Withdraw carbon from the atmosphere (i.e. “negative emission”)
Even though this blogpost is about negative emissions, it is important to me to clarify that the majority of our efforts should be dedicated to the first category. As in so many cases, it is easier and cheaper to avoid damage than to repair it. Vital steps in that direction are: reducing the fossil reliance of our economy, using resources more efficiently, and preventing the release of Carbon from natural carbon-sinks like forests, mangroves or permafrost regions.
Unfortunately, if we want to achieve the 1,5°C goal of the Paris agreement, even a best-case scenario for reducing our emissions is not sufficient. Actually, all Scenarios by the IPCC, which result in a below 1,5°C world, include negative emissions on the giga-ton scale. (global emissions since the industrial revolution are between 300–400 giga-tons). So while the majority of our efforts should go into reducing emissions, we need to invest some part of our efforts in withdrawing Carbon from the atmosphere.
Forms of negative emissions (technologies):
Humans can create negative emission by utilizing technology or by using plants and ecosystems.
Negative Emissions through land-use:
Forests:
Forests are a classic example of creating negative emissions. They store carbon in their biomass, but also increase the carbon stored in the soil. A study by the ETH-Zurich found that there is unused land suitable for afforestation that would accumulate to the size of the USA. And if all of this land was used for forests; “once mature, these new forests could store 205 billion tonnes of carbon: about two-thirds of the 300 billion tonnes of carbon that has been released into the atmosphere as a result of human activity since the Industrial Revolution.” Obviously, there are potential conflicts in land-use for example agriculture. And we have to keep in mind that the carbon is released from the tree again when it rots or burns, therefore a forest can stop being a carbon sink after a certain amount of time or in case of a wildfire.
There is a certain potential for afforestation as a solution but many scientists believe, that planting forrest is only a small part of the solution. David McKay, author of the book “Sustainable Energy - without the hot air”, came to the conclusion that every European would need an area the size twice of Britain to match the rate of emission with the rate of uptake by the forrest. Therefore he and many others concluded that planting trees is a solution that does not add up.
But in any case the partial contributions are still valuable to reduce CO2 concentrations in the atmosphere, and additionally forrest are important for many more reasons than storing carbon. So no bashing on tree-planter and tree-huggers please. Btw also here, it is important to note that existing forests are far more effective in storing carbon than newly planted forests.
Soils in Agriculture:
It is maybe unexpected or even disappointing to hear about soil when you came to this blog post to hear about a cool technology solution. But agriculture plays a very special role in our quest for ending the climate crisis. Agriculture currently makes up a big chunk of the global emission and has in contrast to the other chunks in this pie chart, the possibility to transform itself from an emitting to sequestering industry.
This has mainly to do with soil. The American NGO Carbon180 states that “U.S. agricultural soils alone have the capacity to sequester up to 10% of domestic greenhouse gas emissions annually for as little as $10 per ton.”
There are a lot of elements to so-called regenerative agriculture, but two essential aspects are increased biodiversity (fewer monocultures) and not exposing the soil. If you are interested to learn more about that, I can highly recommend this small explainer/documentary-video by Ecosia.
Agroforestry:
Agroforestry is a land-use management practice that largely overlaps with regenerative-agriculture. It is about combining trees with crops and/or livestock to create mutual benefits between the species, to make them more resilient and productive and has ecological and economic benefits. It lies between afforestation and agriculture. So I put it as a separate solution.
Negative Emissions Technologies (NETs):
BECCS:
BECCS stands for Bio-Energy with Carbon Capture and Storage. 🤨.Let me explain. Bio-Energy is about gaining energy from biomass, for example, by burning it. So if we were to grow an extra forest and then burn the wood to gain electricity, we could call that carbon neutral. This is were the CCS part comes in play. An example of CCS would be to capture carbon at the end of the pipe of a coal plant and then storing it in building material. In that example, it leads to a coal plant being less carbon positive. But if we start off by planting a forest, instead of using coal. The trees would take carbon from the air, we would burn them, gain energy, and prevent the carbon from entering the atmosphere by capturing it and storing it permanently.
There is definitely potential in this solution, but it also comes with a lot of critiques since it could pose conflicts of interest in the use of land. Our population is still growing, we need land for food production, and currently, agriculture is the leading cause for deforestation.
DAC:
Finally, a magic machine that can suck carbon out of the air. That’s what DAC stands for Direct Air Capture. And yes it exists, it works, and it is operational. I am a big fan of this technology and subscribed to some “carbon removal services”, and can watch the sequestered CO2 grow in my personal impact report. The Carbon can be used to fizz drinks, in actual greenhouses, in building materials or it can be stored in solid rock formations.
The challenges to this technology are the energy use and price per ton.
If we generate the energy for DAC by burning coal, this will not get us anywhere. Therefore, clean energy is a crucial first step to enable this technology to unfold its potential. Luckily, it does not really matter where the DAC-plants are located since the amount of carbon in the atmosphere is spread mostly equal. This is why Climeworks located their first plant in Iceland, “where about 85% of the total primary energy supply is derived from domestically produced renewable energy sources” (mostly geothermal).
The other challenge is the price. Currently, the cost lies between 400 and 1000 dollars per ton. This is too expensive to cover it with a carbon tax. But DAC is a relatively young technology, and the price is expected to drop as more research is done, experiences are made, and operations are scaled. This is why it is critical to support this technology now because we need it asap, and it needs to evolve fast.
Moreover, there is not only Climeworks but also Carbon Engineering and Global Thermostat as the most prominent players, if you want to look closer into it.
Interestingly enough, big oil companies are invested in this technology. This is maybe due to their interest in synthetic-fuels, also called Solar-Fuels. These could be produced from the captured carbon, water and sunlight. Similar to DAC, this technology is operational, but currently too expensive.
Burning these fuels would be carbon neutral because only the amount of carbon is released that has been captured before. Compared to the current implications of burning fuel, that would be a giant leap. This would be especially important for industries that are difficult to electrify, such as planes and freight ships. Since these need energy carriers with a high energy density, today liquid fuels store 20 to 60 times more energy in the same volume compared to batteries. And compared to hydrogen they require much less sophisticated infrastructure. Which poses a severe hurdle in many regions.
Resume
I hope this blogpost was insightful and a joy to read. I think it is safe to say that there are sound solutions to create negative emissions. But these are by no means an excuse to delay a radical transition of our economy and society. These solutions are essential but should function as clean-up tools when we reached a carbon-neutral economy. Or as a vital buffer to gain a bit more time. There is no single solution and no easy solution for the climate crisis. We should not wait for a magical machine to solve our problems. But we should change our lifestyles and our economies, and we should support the magical machines we already have such as trees, oceans and soils. And ensure to bring the cost down of the magical machines that we invented like DAC. But these techno-fix solutions should not soothe a strong movement towards a lifestyle that is in harmony with our environment.
Abbreviations that can be confusing, if you read more sophisticated articles:
Additional Reading / Sources:
Ecosia documentary about regenerative agriculture: https://www.youtube.com/watch?v=TPkXAi_IKwQ
Carbon180: https://carbon180.medium.com
Solar fuels paper: https://www.cell.com/joule/pdf/S2542-4351%2819%2930373-3.pdf
Solar fuel video by ETH Zürich: https://www.youtube.com/watch?v=s1-soaZn4B0
David McKays great book, which you can download for free: http://www.withouthotair.com
Carbon Cycle: https://www.noaa.gov/education/resource-collections/climate/carbon-cycle
Global Carbon: https://www.fs.usda.gov/ccrc/topics/global-carbon
Global greenhouse gas emission data: https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data
Environmental emission of carbon dioxide CO2 when combustion fuels like coal, oil, natural gas, LPG and bio energy: https://www.engineeringtoolbox.com/co2-emission-fuels-d_1085.html
