Twelve clear trays with rock dusts and other materials from our experiments, from white and ochre to dark red and black

What we do / Scientific Research

Enhanced Rock Weathering Research

What is enhanced rock weathering?

Enhanced rock weathering (ERW) is a carbon dioxide removal (CDR) method where crushed rocks are added to the soil. We speed up the natural weathering process by several orders of magnitude by grinding the rocks and putting them in a favorable place.

Grind. Rock such as basalt is ground to dust. The finer the grains, the more surface there is to react.
Spread. The dust is spread on farmland, like lime or fertiliser.
React. In the presence of water, the rock dissolves through a chemical reaction that changes CO₂ into bicarbonate (HCO₃⁻).
Store. The stable bicarbonate traps the carbon as it travels through rivers to the ocean, where it can remain stored for over 10,000 years.

Six glass beakers in a row holding growing amounts of grey basalt dust, labelled 10, 20, 40, 100, 200 and 400 t/ha, with a toy figure in a safety vest on the left and an orange folding rule on the right — How much rock dust is that? Each beaker holds as much basalt as its base, 5 cm across, would receive at the application rates of our experiments. The three on the left, 10 to 40 tonnes per hectare, are common rates in practice.

In practice, the hard part is not the spreading. It is measuring how much CO₂ a field really removes, and that is what our experiments are for.

The field is young: in 2025 enhanced rock weathering accounted for about 3,800 of the 2 million tonnes of CO₂ that all newer removal methods took out of the air.

Source: The State of Carbon Dioxide Removal, 3rd Edition, June 2026, page 162.

Information board with the words Project Carbdown at the edge of a meadow; behind it, out of focus, a tractor pulls a red spreader across the grass — Spreading 27 tonnes of basalt on one of our experimental fields in Fürth, April 2022.

1. Scientific Research

Leading Global Research in Enhanced Rock Weathering

Alongside many others, we believe that enhanced rock weathering will become a crucial component of the CDR toolkit in the future. However, the CO₂ removal effects of enhanced rock weathering in soils are not yet fully understood and in-situ measurements continue to pose significant challenges. Since 2020, we have contributed to this global scientific endeavour through multiple field and greenhouse experiments with extensive data collection. Our focus is on high-frequency lab measurements and continuous 24/7 monitoring using hundreds of electronic sensors in large-scale experiments spanning several years. Our aim is to identify which soil and rock combinations are most effective, or in some cases ineffective, at CO₂ removal. There are three main field and greenhouse experiments, the latter likely being the largest ERW experiment on the planet. We publish new data and results every few weeks in our blog.

Panorama of the greenhouse: two long tables with rows of black pots, most of them with tall green grass, under a white shade cloth — Our greenhouse experiment. Each pot is one experiment: one soil, with or without rock dust.

Field trials in Fürth and Greece2021 to 2025
Basalt and olivine-rich rock dust spread on fields, observed by soil sensors.
XXL lysimeters in Fürthsince 2022
20 buried soil tanks of 300 litres, with up to 400 tonnes of basalt per hectare.
Greenhouse experiment 2023/20242023 to 2025
Up to 400 pots with 17 soils and 14 rock materials.
Greenhouse experiment 2025/20262025 into 2027
Designed for more than 500 pots in two greenhouses: more soils and rocks, fewer replicates.

Our main experiments since 2021. Each bar runs from the set-up to the last data we have published. A fading end means we have no end date.

Our experiments are conducted in partnership with scientists from the 17 universities and research institutes shown below. Our research network also includes the scientific teams of the CDR startups we have invested in.

On standards for measuring and certifying enhanced rock weathering we work closely with Cascade Climate, Isometric and the Ithaka Institute.

Scientific collaborations 17 institutions

Enhanced rock weathering standard development 3 partners

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Our Experiments in Pictures

Photos from our field trials, the XXL lysimeters and the greenhouse, in the order in which it all happened. Select a photo to enlarge it. The arrows on the screen and the arrow keys take you to the next one.

Twelve clear trays in two rows, each holding a different rock dust or granulate, in colours from white and cream to ochre, brown, grey and black

Rock dusts and other materials from our experiments

Twelve small heaps of soil in different shades of brown, numbered 1 to 12 by hand on a white sheet

Twelve soils side by side

Aerial view of a tilled strip of field beside a red barn, with one round plot marked by a pale ring and a darker round plot next to it; two vans, a trailer and a few people stand at the edge

Setting up the first field trial in Fürth, April 2021

Four people with dust masks carry buckets and scatter rock dust by hand on bare soil, dust hanging in the air

Spreading basalt by hand, April 2021

Aerial photo of a meadow beside a red barn with three round plots mown into the tall grass, labelled 0, 1 and 2, four small letters c, a 100 metre scale and a compass rose

The test plots of the first field trial from above

Small barn with a red roof on open meadow land under a heavy sky glowing orange-brown, a village on the right

An orange sky over the field site in Fürth, March 2022

Tractor pulling a red spreader trailer that throws dark basalt dust onto a meadow at the edge of a forest

Spreading basalt dust on grassland, 2022

Aerial view of a mini excavator and a wheel loader digging a long trench at the edge of a meadow while a person watches

Digging the trench for the XXL lysimeters, 2022

All parts of one lysimeter laid out on pavement: tank, two beer crates, grid plates, fleece and mesh, blue tubes, a camera and six wireless sensors

All parts of one XXL lysimeter

A helper standing in the trench and setting the first green tank into place, with a bag of filter sand beside the trench

The first tank goes into the trench

Helpers filling soil into a long row of green lysimeter tanks set in a trench, one compacting the soil with a red hand tamper

Filling the tanks with soil

A black sensor with an orange label lies at the bottom of a hole in brown soil, an orange folding rule beside it

A soil sensor goes into the ground

Hands tipping a portion of earthworms from a plastic tray onto the soil of a lysimeter

Earthworms for every lysimeter

A man sits at a makeshift table and holds a probe into a small sample bottle, a handheld meter and brown sample bottles in front of him

Measuring water samples with a handheld meter

Field camera view in the rain: a person in an orange rain jacket and shorts stands in wet grass beside the row of lysimeters, a red van parked next to them

Heavy rain, August 2022: Ralf Steffens pumps water out of the lysimeters that hold extra electronics

Wheelbarrow piled high with cut cosmos plants on the lawn of the experiment site, a brick barn behind

Harvesting the plants to weigh the biomass, 2022

A full rainbow arches over green meadows and trees under a blue sky with clouds, the red barn of the field site on the right

A rainbow over the field site in Fürth, September 2022

Rows of black pots filled with bare soil, each with a white drip ring and a printed label, connected by thin tubes on a greenhouse table

Pots with fresh soil on the greenhouse table, 2023

About twenty team members sit on benches along a long table in the greenhouse and smile at the camera

The team that set up the greenhouse experiment, March 2023

Black lysimeter pots with sprouting grass, drip rings and Project Carbdown labels, connected by tubes on a greenhouse table

The greenhouse experiment with young grass, autumn 2023

Four long rows of small sensor units with lit displays, wired to power strips on a wooden floor

A test run for dozens of sensors

Four grey tubes standing upright, each topped with an orange and yellow unit with a small display, connected by cables to a hub on a tiled floor

Four of our self-built CO₂ sensors

A team member working with pliers behind rows of pre-assembled fluxmeter electronics and a pile of ribbon cables

Assembling the fluxmeters by hand

Six transparent fluxmeter chambers glowing green and white on a lawn at night during a test run

Fluxmeter chambers on a test run at night

Long-exposure night photo: short star trails and a pink aurora glow above the horizon, the barn and the lights of the village below

Aurora and star trails over the field site in Fürth, May 2024

Wide-angle view of a greenhouse table full of lysimeter pots topped with transparent fluxmeter chambers and controllers

Fluxmeter chambers measure the CO₂ that leaves the soil

Four small orange-framed displays labelled Carbdown CO2 Sensor, mounted on the side of a black pot and showing readings such as 2216 and 4064

CO₂ readings from four sensors on one pot

Eight people stand smiling behind rows of grass-covered pots in the greenhouse, one of them holding up a phone for a selfie

A group photo among the pots

Two men in winter jackets and hats talk on a farm track beside a snow-covered field, one leaning on a long metal sampling rod, an orange bucket on the ground

Jens Hammes and Ralf Steffens during fieldwork in the snow, late 2024

Upturned soil column with fleece and sand layer on top, a hand holding the label 6.0.A against soil riddled with small worm tunnels

A soil column after two years, ready for sampling

Red-capped sample tubes with handwritten pot codes, sorted in pairs into plant trays

Samples sorted in plant trays, 2025

Rows of labelled zip bags with tea bags laid out on a greenhouse table

Tea bags awaiting analysis

A crane truck loaded with white big bags stands in front of a brick barn; one person sits on the truck bed, another stands beside it

Big bags arrive by crane truck, April 2025

Aerial view of a paved yard beside the greenhouse with a long row of white big bags along the fence, a mini excavator and blue tarpaulins

Big bags lined up next to the greenhouse

Seen from above, six people stand on a blue tarpaulin around a mini excavator and fill material into white sacks

Preparing soil with a mini excavator

The greenhouse experiment on film

Our 15-minute documentary tells the story of the greenhouse experiment from 2023 to 2025: how we built it, what went wrong, what we found and how we took it apart again.

Documentary: Carbon Drawdown Greenhouse Experiment 2023-2025Video by Dirk Paessler. Loads from YouTube when you click.

What We Have Found So Far

16 of 49

soil and rock combinations in our greenhouse removed at least 0.5 tonnes of CO₂ per hectare per year. Two years of greenhouse data

1,400 days

outdoors, and our 20 lysimeters show no significant sign that basalt removed extra CO₂ (and our specific soil is the reason). The lysimeter series

More than 10 times

more of the weathering products stayed in the two soils we examined in detail than left with the water. Our preprint on alkalinity

0.95

correlation between cheap conductivity sensors and alkalinity across the whole dataset, but not for every single soil and rock combination. The MRV proxy series

All greenhouse posts

All field and lysimeter posts