Expert meeting on enhanced rock weathering in Paris
This spring, researchers, students, interest groups, non-profit organisations & startups met at the Ecole Normale Superieure in Paris to discuss the barriers and opportunities for enhanced rock weathering in Europe. The workshop aimed to facilitate exchange among different actors around enhanced rock weathering, a technique which aims to remove carbon dioxide from the atmosphere by spreading crushed rock material on land or coastal areas. When rocks contain silicate they bind carbon dioxide from the atmosphere as they weather. This carbon dioxide is then locked away for thousands of years when the weathered products are transported by rivers and reach the ocean.
Interest in the technology is growing
Interest in enhanced rock weathering is increasing sharply in recent years, but it remains among the least known measures for carbon dioxide removal. The public perception of enhanced rock weathering is rather positive. Among members of the public (in Western nations) most concerns are directed towards its impact on the oceans rather than soils where it is applied in the first place, reports Emily Cox from Oxford & Cardiff Universities. A reason therefore could be that rock dust has a history of use as a soil conditioner in agriculture. Carl Boedecker from ZeroEx reports that some of the German farmers they work with are surprised to learn from their fathers that rock dust was used on the farm in the past. It had been abandoned for economic reasons, thus the 'new' revenues from carbon dioxide removal could lead to a renaissance of its use.
Scaling up will require massive resource
In order to scale enhanced rock weathering to levels required to contribute to climate change mitigation, Cara Maesano, from the RMI, estimates a massive & continued investment of several hundreds of million USD for the USA would be required. What is often forgotten is the large mining sector required to supply rock material which requires the opening of new mines. Otherwise basalt supply can quickly become the main bottleneck for enhanced rock weathering. Opening new mines requires a long time horizon that comes with massive investments, strict regulations, public concerns, and environmental and human rights issues. Today, practical challenges for small sized businesses like ZeroEx & climerocks are related to delivering several truck loads of rock material to farmers and upfront investments for the application of enhanced rock weathering. The latter could become more challenging if proposed shifts in regulation are implemented which would result in payments tracing carbon dioxide removal which occurs over the course of several years after application.
The challenge of quantifying carbon dioxide removal
While regulations for monitoring, reporting and verification are being put in place in the European Union, the quantification of carbon dioxide removal remains a major challenge. While high-resolution satellite observation which resolves single trees are becoming game-changers in monitoring afforestation, it is still a long way before they become suited for monitoring below-ground changes. Tom Reershemius from Yale presented a novel approach for enhanced rock weathering based on mass balance which shows promising results in a field trial, while start-ups present at the workshop are exploring their own approaches. Although there is complexity in tracing carbon dioxide removal in the natural field environment, established literature validates existing approaches, and each measurement approach has strengths and limitations, reports Christina Larkin from Inplanet. While modelling capabilities are improving, they still largely focus on tracing abiotic and inorganic carbon impacts ignoring the response of organisms and organic matter.
Environmental side-effects remain largely unknown
The side-effects of enhanced rock weathering on biology are getting into focus of research, but still we know little how plants and soil organisms respond to enhanced rock weathering. As rock material once applied is virtually impossible to remove, its consequences can be long-lasting, says the organizer of the workshop, Daniel Goll. Harun Niron from Antwerp University which shows new evidence from experiments in pot which confirm that soil organisms like microbes and earthworms are affected by rock material applied and even can affect weathering rates. Results from a field trial in a rubber plantation shows that enhanced rock weathering improves soil fertility, tree nutrition and multiple ecosystem services, as reported by Maoyan Bi and Zuoqiang Yuan from Northwestern Polytechnical University. The application in forestry and reforestation, which is rarely considered, has the potential to contribute to efforts in reducing global warming during the next decade, as Yann Gaucher from the LSCE reported. enhanced rock weathering can't do the job alone, but it can be an important part in a portfolio of carbon dioxide removal technologies. Katsumasa Tanaka from the LSCE stresses that an over-reliance on carbon dioxide removal technologies, may inadvertently jeopardise near-term mitigation efforts. This reminds us of the utmost importance of prioritizing the emission reduction from fossil fuel combustion.
The risk of application outpacing scientific understanding
A concerted effort is needed in order to fill gaps in our understanding of enhanced rock weathering. Companies play an important role due to their plans for a massive roll-out of enhanced rock weathering. On the one hand, this poses the risk that application outpaces scientific understanding and therefore its safe use. On the other hand, it can provide opportunities for accelerated understanding if data and knowledge is shared. In the future, tailored feedstocks instead of recycling mining trials could help to reduce costs & provide the right solution for a large range of end users, reports Benjamin Moeller from ZeroEx. However, as Emily Cox reported, this runs the risk of encountering more negative public attitudes, as well as environmental and legislative challenges.
Ways forward
foster joint actions between academic and private sectors
jointly monitor organic and inorganic soil carbon responses to ERW
develop open-source modelling solutions tailored for stakeholders
deploy holistic approaches integrating geochemistry, ecology & sociology
The workshop was organised by the CLand Convergence Institute funded by the French government which researches land-management solutions for managing the ecological and energy transitions of the 21st century. The recordings of the presentation are freely available on our youtube channel.