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The IPCC’s 2018 special report on the impacts of global warming of 1.5° above pre-industrial levels specifically famously stated that the 1.5° target can only be met if CO2 is actively removed from the atmosphere. An approach that the IPCC stuck to in their report of this year. Of course, continued delays in large-scale mitigation of emissions would only increase the need for negative emissions. And as the removal of CO2 is itself significantly more laborious than mitigation measures, delayed action will have serious economic consequences.
For some years, enhanced weathering has played an important role in the portfolio of proposed carbon dioxide removal (CDR) strategies, alongside afforestation/reforestation, direct air capture and bioenergy with carbon capture and storage (BECCS) among others. Enhanced weathering relies on the geological process of chemical rock weathering, which naturally consumes and regulates atmospheric CO2 levels over millions of years, storing the sequestered carbon in carbonite minerals.
The modern method of enhanced weathering speeds up this geologically gradual process by grinding suitable rocks to flour-like grain-sizes (to radially increase the reactive surface area) and spreading them onto agricultural land – although my recent research has shown that coarser grains can yield higher sequestration once total surface area is controlled for. The method works best in humid regions, as water is needed for the reaction and weathering speeds increase with temperature. As such, (sub-)tropical regions are best places to achieve the highest rates of carbon removal by weathering.
Recent desk and lab studies are showing that enhanced weathering is cost competitive with other CDR methods (in the range of $50-300 per tonne of CO2 removed) with an overall potential as high as 5 gigatonnes of CO2 removed per year.
Yet while BECCS is prominently represented in global studies and models, enhanced weathering features to a much lesser extent. The main reason for this is the current state of the research. Today, the studies reporting actual field results can be counted on the fingers on one hand. This implies that uncertainties are still high and the real-world implementation of this method will have to wait, while other approaches like direct air capture¹, biochar or even the CCS aspects of BECCS are starting to report actual carbon sequestration, albeit in negligible quantities.
So, while enhanced weathering relies on already existing technology and has theoretically been proven to provide substantial CO2 sequestration potential, the practical evidence is lacking. This is what needs to change.
A connected challenge is the difficulty of monitoring the CO2 sequestered by enhanced weathering projects due to the highly diffuse uptake of CO2 in agricultural soils and the fact that any additional CO2 dissolved in rainwater is nigh impossible to capture, measure and attribute. We must also take into account the fact that the nutrients contained in rocks like basalt (a favoured choice for enhanced weathering) are likely to fuel additional plant growth, potentially enhancing CO2 uptake by 50% in a virtuous circle that would be deserving of additional carbon credits.
By contrast, direct air capture or bioenergy-based projects for carbon removal often claim to provide a single-point quantity of CO2 which can easily be gauged, yet these are often only methods of capturing CO2 and do not solve the long-term storage question. This is a problem for enhanced weathering as, clearly, before these projects can be used in a carbon emission trading scheme (or any other kind of compensation mechanism) it must be clear how sequestered CO2 is measured, reported, and verified (MRV). Only if the sequestered carbon can be properly accounted for will it ever be economically interesting and attract large-scale investments beyond venture capital. Research in this direction is just starting but needs to speed up.
One step forward, fourteen steps back
To solve this crucial issue, more money needs to be spent on research. The EU spent up to €10 billion on environmentally relevant research and development in 2019, while subsidizing the fossil sector with more than €137 billion. Of course, this is comparing apples to pears, but the sheer discrepancy alone (a factor of nearly 14) should raise eyebrows.
Funds have to created which are accessible without bureaucratic hurdles. For example in Germany, scientists can apply for EU grants like this one, but the process remains painfully slow. On top of this, the success rate is low (roughly one in three in the EU and Germany). Once you have acquired a grant, you may still be distracted by extensive paper work or see funding withdrawn.
Funding problems like this apply to all CDR methods, but enhanced weathering suffers particularly from the unavoidable fact that the process of weathering is slow. Even if sped up by an order of magnitude or two, measuring reliable and generally applicable results is almost impossible given the limited resources. Given that enhanced weather is always identified as a promising CDR solution, this needs to change, so that we may all better understand the scale of the contribution it can make.
The necessary investment in enhanced weathering research could come from private investors, entrepreneurs, and philanthropists, who acknowledge the need for speed. But this, of course, comes with its own risks in terms of democratic buy-in and transparency.
With wildfires getting out of hand, rivers drying up, and heavily unfair subsidies for the fossil fuel industries, the younger generation now sees what will be in store for them in the future and is beginning to take matters into their own hands, responding with radical methods like gluing themselves to roads and paintings. With this in mind, it seems cynical have yet another meeting to define roadmaps, discuss proposal texts and compete for as yet only pledged money from public funds.
Dr Thorben Amann is a postdoctoral researcher at the University of Hamburg. He specialises in geology and his recent publications have focused on carbon flux in relation to negative emissions.