Introducing “Project Carbdown”: Our first “enhanced weathering” field trial aims to remove CO₂ from the atmosphere
90% of Iceland is basalt, a great rock for enhanced weathering (Photo by Dirk Paessler).
Zur Deutschen Version/Go to German version
The weathering of rock permanently binds CO₂ from the air and thus removes it from the atmosphere. Can this be used to mitigate climate change? For a few months now, we have been preparing a scientific project together with several scientists and our partner Fieldcode in which we want to accelerate and measure the weathering of rocks, in order to possibly expand the toolbox for climate protection.
Today we are proud to announce: Project Carbdown.
Introduction
To support the global effort to mitigate climate change one goal is to find a set of solutions that - on a global scale - can potentially scale up to collect ~10 gigatons of CO₂ annually from ambient air between 2030 and 2040 (based on calculations in the SR15 by the IPCC). We believe that enhanced weathering will become an important method among these carbon removal solutions. In our blogpost “Let's do something with enhanced weathering” we describe our reasons for looking at EW and in our Interview with Professor Jelle Bijma he explains why he thinks that only nature-based solutions like EW will be able to master this job.
In recent weeks we - together with several experts from different academic fields - have come up with a plan for a field project that we are conducting in 2021. Let’s have a look!
What do we need to stop climate change?
To limit climate change to 2 or even 1.5 degrees Celsius we must reduce emissions, eventually stop emitting new CO₂ and we must remove CO₂ from the atmosphere - which is called Carbon Dioxide Removal (CDR). CDR technologies and/or processes that are suitable for this endeavour must meet three major criterias, among others:
Scalability: The technology must be scalable into megatons of CO₂ removal per year.
Speed: The CO₂ removal must happen over just a few years, not decades or centuries.
Permanence: The collected carbon must be stored in safe and permanent storage.
Also cost, use of land, energy, and potential side effects must be kept in mind and limited as much as possible.
CDR with enhanced weathering seems to check all these boxes! Let us explain:
Our idea
The basic idea of Project Carbdown is to incentivize the spreading of rock powder along with biochar on agricultural fields which lead to the removal CO₂ from the atmosphere through a process called “enhanced weathering.” This allows farmers to sell CO₂ removal credits along with their produce, giving them extra income. This process may also provide additional co-benefits such as increased crop yields through improved soil pH and nutrient addition delivered by the rock (which will partly replace fertilizer and lime).
In the end, a farmer should be able to make an additional income of several hundred Euros per year per hectare of farmland, while at the same time fighting climate change (we expect a CO₂ price of ~€100/ton in a few years).
Given the massive size of farmland and quantity of fertilizers currently used on our planet, this concept has the potential to scale globally to megatons and even gigatons of captured CO₂ in the future.
How does it work?
When certain rocks like basalt or dunite (~90% olivine) are exposed to the ambient air their surface starts to chemically react with the CO₂ in the air. In this process, the minerals these rocks are made of react with CO₂ and water to form harmless carbonates. These dissolved products either remain in the soil, or wash away via rivers and ultimately end up in the seas, where they help improve the ocean alkalinity. This can potentially help counteract the acidification of the oceans - a troubling side effect of climate change. From there, animals like corals use the carbonate to build their skeletons and eventually it precipitates to form sediments on the seafloor. The removal is permanent as the CO₂ remains locked into geologic formations like the Dolomites in the Italian Alps.
Mineral weathering is Earth’s natural long-term carbon removal mechanism that normally takes hundreds of millions of years. Every year about 1 Gigaton of CO₂ is naturally removed from the atmosphere this way. But us humans are adding 40 Gigatons to our atmosphere each year, so this is by far not enough. Through intentionally selecting the optimal minerals and using farming to accelerate the weathering rate, we can speed up this process so that it is relevant on human time scales for CDR. One ton of rock can remove between 0,1 and 1 ton of CO₂ depending on rock type and other parameters. With the amount of land currently under cultivation, we believe enhanced weathering paired with farming offers us an ideal and untapped tool with massive potential to help humans fight climate change.
What are the problems and our solutions?
There are five problems:
Problem 1: The natural process of weathering is slow in part due to the limited rock surface area available for reaction with atmospheric CO₂.
The solution to this first problem is to grind the rocks to small particles like sand or powder: This massively increases the surface area between the reactive minerals and ambient air and thus the CO₂, which dramatically speeds up the weathering process compared to the natural, geological process.
Problem 2: Only a tiny fraction of the ambient air is CO₂ (0,04%), which also limits the speed of the weathering process.
The second problem can be mitigated by mixing the rock flour into farmland soil. This will considerably speed up the CO₂-removal process because there is so much more CO₂ in soil than in the air (usually ten to hundred times more due to plants, roots, bacteria, etc.).
CO₂ in ambient air: 415 ppm; CO₂ in soil: between 400 and 40.000 ppm
Problem 3: Large land areas are needed in order to remove huge amounts of CO₂.
This third problem can be solved by using farmland for CO₂ removal that is at the same time used for crops so there will be no competition for land use.
Problem 4: There is no reliable accounting for land-based CO₂ removal yet which is necessary for the farmers to get paid for the CDR work on their farmland.
The solution to this problem will be a smart monitoring concept in the fields used for CDR. Our goal is to enable science and make fast progress with regard to developing a robust method to determine the rate of permanent CO2 sequestration and ultimately solve the CO₂-accounting problem.
Problem 5: (Almost) nobody has actually done this in practice or at scale. Although there are hundreds of scientific studies about enhanced weathering, to date very few experiments have been conducted on actual farmland. The main reason is that there has been almost no scientific funding so far.
Our goal is to speed up the scientific work by immediately enabling experiments and field work without waiting for usually slow public funding processes.
Our experimental design will of course obey all EU/German regulations for farmland amendments. We hope to demonstrate that our concept actually works to permanently (i.e. on human time scales) remove substantial amounts of CO₂ in a verifiable way without creating massive downsides (e.g. lowering the crop yield or release of toxins). If this is demonstrated, we believe there is potential for enhanced weathering with farming to be considered as a common carbon dioxide removal and climate change policy for countries worldwide.
Practicalities
So what are we actually going to do in 2021 and eventually 2022?
We will run experiments where different types and forms of rock dust will be spread on farmland before the crop is planted/seeded. Throughout the year we will measure various parameters (soil, chemistry, weather, crop size) using automated and manually collected measurements and samples.
In parallel we will run lab experiments with the same material and similar setups along with pot experiments in a greenhouse so we can later compare the results from the field with those from the lab/greenhouse, where we have more control over the ambient parameters.
Step 1: Select locations and materials
We are planning to use three fields, two in Germany and one in Greece. We will be using basalt and dunite, both quite common rocks, combined with biochar.
Step 2: Prepare the farmland/crop
Just before the vegetation season we will use a cultivator (dt. “Grubber”) to prepare 90 m long stretches of the field, each 3 m wide, and mark 12 m long plots. Then we will spread various combinations of basalt, olivine and biochar on random plots, leaving some plots untouched for reference. After spreading, the cultivator will again go over the plots to mix the rocks into the upper crust of the soil.
On our plots we will apply 4 kg of rock per m², corresponding to 40 tons per hectare, plus 0,2 kg of biochar per m². So the theoretical amount of CO₂ we expect to capture with the rocks is between 4 tons and 40 tons per hectare. The main question we want to answer is how long it will take.
Afterwards the usual crop is planted/seeded (e.g. corn, cotton, elephant grass) and we will install various measurement devices into the plots, including sensors for pH, alkalinity, moisture, temperature, conductivity, etc. plus lysimeters for water samples.
Step 3: Wait and monitor
Now we will wait and watch the crop grow. In case there is very little rainfall we will irrigate the plots (weathering reactions require water). The automated measuring systems will constantly deliver various measurements, e.g. temperature, moisture, conductivity, pH, and other metrics. Additionally, at regular intervals water samples will be collected and analysed in the lab to monitor side effects.
Step 4: Harvest and measure
In the fall we will harvest the crop, measure the results and soil metrics for each plot with different setup and rock-combinations used. Also crops and soil will be analysed for traces of toxins and improved carbon uptake due to the expected soil improvements.
Step 5: Analyse and report
Until the end of the year we will prepare and publish an initial report with a preview of our results. Also we will share notable results throughout the year to inform the public and attract others to join this project.
Our goals
For 2021
At the end of 2021 our goal is to be able to tell how much CO₂ has been removed from the atmosphere per m² in one year. We want to be able to assess possible side effects and come up with a simplified and easy to use monitoring concept for the CO₂ removal (what metrics will work well?). We then plan to test further in 2022.
Supporting the 2050 carbon neutrality goal of the EU and Germany
Based on our initial calculations if every farmer would use this practice Germany could potentially become a substantial building block for Germany’s carbon neutrality pledge for 2050 and for negative emissions for the future. An average German causes 10 tons of CO₂ emissions per year and there are almost 17 million hectares of agricultural land in Germany. We suggest applying 40t/hektar annually. If it takes 5 years for the basalt to weather (optimistic estimate) we would reach an annual run rate of 100% = 40 tons of CO₂/hektar in the 5th year of annual basalt application. The key point is that both figures are in the same order of magnitude (83 mio Germans x 10 tons = 830 megatons, 17 mio ha x 40 tons = 680 megatons).
FAQ
Will there be enough rocks to scale this concept into megatons and gigatons?
Yes, there is plenty.
Can we mine and crush enough rock to make a difference for the climate?
Yes. According to IPCC scenarios globally we might need to remove 10 gigatons of CO₂ per year, which requires ~10 gigatons of rocks per year. For comparison: currently 50 gigatons of sand and gravel are moved by humans annually on the whole planet, plus coal, ores, oil, etc.
Mining and grinding the rocks will require energy. Are you sure that your approach will not create more CO₂ emissions than what you can collect?
There are several scientific reports which have calculated this and they all concluded that this can be reasonably CO₂ negative even if fossil energy would be used. Preferably renewable energy should be used for mining, transport and grinding, of course. In any case the project will monitor this via a life cycle analysis.
People involved (in alphabetical order)
Prof. Dr. Jelle Bijma (Alfred Wegener Institut, Germany).
Dr. Mathilde Hagens (Wageningen University & Research, Netherlands)
Prof. Dr. Jens Hartmann (University of Hamburg, Germany)
Dipl.-Ing. Dirk Paessler and Ralf Steffens (Carbon Drawdown Initiative, Germany)
Dr. Ingrid Smet (Fieldcode, Greece)