In a past blog, I investigated how veganism can help solve many environmental and food security issues. However, there are other solutions out there and this week I thought I would look at something new.
After last week’s blog, I was researching more solutions to our fertiliser problem and I found this interesting tweet.
Figure 1: Carbon Brief's enhanced weathering tweet
Therefore, I decided to research enhanced weathering (EW) to see if it is a good alternative to nitrogen fertilisers and also investigate how it can remove CO2 from the atmosphere and contribute to food security.
What is enhanced weathering?
EW is a carbon dioxide removal (CDR) geoengineering technique, which aims to alter the Earth’s natural systems to counteract climate change. CDR techniques aim to reduce CO2 after it has been emitted into the atmosphere and this occurs by increased photosynthesis (figure 2, 1-5) or by abiotic chemical reactions (figure 2, 6-7).
Figure 2: Mitigation and geoengineering techniques a) mitigation, including carbon capture and storage (CCS) and carbon capture and utilization (CCU) b) carbon dioxide removal (CDR) geoengineering techniques c) Radioactive forcing geoengineering (RFG) techniques.
Natural chemical weathering processes draw CO2 out of the atmosphere and sequester it in rock minerals (such as silicates found in basalt). This works as cations are releases during weathering processes which bind to CO2 forming bicarbonate and carbonate ions. EW aims to speed up this process through dispersing ground silicate rocks with a larger surface area to volume ratio (figure 3).
Figure 3: Enhanced weathering process
Currently, the Leverhulme Centre for Climate Mitigation is working on the UK’s largest geoengineering project. They aim to deliver transformative understanding of EW both as a negative emission technology and a way of achieving resource-efficient food security (figure 4).
Figure 4: Leverhulme Centre for Climate Mitigation introduction
Is enhanced weathering a good idea?
Geoengineering techniques seem good in theory, but they are often expensive, have limited effectiveness or have potential safety risks (figure 5). Figure 5 shows EW is highly effective but has medium-low affordability. In 2009, the Royal Society marked EW as one of the safest techniques, but it has since gone down to a medium safety rating. Despite this, it is still one of the most promising geoengineering techniques we have today (figure 6).
Figure 5: The effectiveness, affordability, safety and timeliness of different geoengineering techniques. Arrows indicate changes in the assessment since the Royal Society report and abbreviations in blue refer to academic studies assessing each technique.
Figure 6: Enhanced weathering benefits
In the next section of the blog, I will draw on several academic studies to critically assess whether EW is a good solution for both climate change and food security.
Climate change
Applying 50 tonnes of basalt per year to 70 million hectares in North America could sequester as much as 1.1 billion tonnes of carbon dioxide in the future. To do this, more than 3 billion tonnes of basalt is needed– equivalent to almost half the current coal production. Mining and crushing rocks would be needed adding to deforestation, biodiversity loss and carbon dioxide emissions. However, a 2014 study found that even in a pessimistic scenario, CO2 sequestration from EW would be almost 3x that of mining, crushing, transport and application emissions combined (figure 7). Furthermore, they noted the added benefit of EW improving the efficiency of other CDR techniques, including biochar and afforestation.
Figure 7: Carbon dioxide budgets per tonne of rock in an optimistic and pessimistic scenario. A represents the maximum carbon dioxide sequestration per tonne of rock for each scenario.
Despite these promising figures, a 2012 paper noted there are uncertainties in CO2 budgets due to differing weathering rates. Furthermore, it puts operational costs of EW at $52-480 per tonne of CO2 sequestered which is greater than $39-100 per tonne for bioenergy with carbon capture and storage (BECCS).
Food security
Silicon released from weathering products is a beneficial nutrient for many plants as it allows resistance to certain diseases and increases crop yields. This reduces the need for fertilisers and helps prevent issues associated with excessive reactive nitrogen use (explained in last week’s blog). However, a 2017 study noted that EW with materials such as olivine could cause toxic heavy metal contamination of food.
Furthermore, EW increases the pH of soils and waters having potentially negative ecological consequences, especially in peatlands where some species have adapted to a low pH. However, in other areas the increased alkalinity would help combat ocean acidification.
Is this the solution we have been waiting for?
Every paper I have read concluded with the same statement – there is more research needed to understand how EW could be implemented and to recognise the potential ecological and societal side effects. This made it clear that this technique is not ready for widespread implementation. However, I will be keeping up to date with the Leverhulme Centre for Climate Mitigation progress with bated breath.
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