Earth Science Asked on September 5, 2021
A recent Guardian article "Spreading rock dust on fields could remove vast amounts of CO2 from air" has gotten some attention in the nongovernmental and UN organizations working in the Sahel who are desperate to combat the adverse effects of climate change in the region. This article is based on a Nature publication on enhanced rock weathering (ERW).
Let’s pretend a large international organization has tasked a newly employed software developer to look into the feasibility of performing ERW in the Sahel. Now this let’s say this software developer, who has no geological background whatsoever, is trying to figure out what it would take to run a ERW pilot in the Sahel and decided to investigate Bol, Chad to have a specific place to focus on.
Ideally, this pilot would seek to test two things (i) is ERW feasible to perform in the region of conflict, (ii) does the crushed basalt or silicate, which is added to the soil, increase crop yield?
In order to determine if this pilot is feasible to even consider I think the following should be investigated:
What else should I look at?
If you were given this (completely hypothetical) task where would you start?
Is there any giant red flag I am missing which would be enough of a reason not to move forward with a pilot?
More information on ERW here:
Farming with crops and rocks to address global climate, food and soil security
Hot climates are good for ERW -- the kinetics of weathering are temperature dependent. But as noted above you need water too.
Answered by David Beerling on September 5, 2021
Note that the sahel is a lost cause for the rainfall/CO2 absorption side of the equation. Heat tends to mineralize soil and reduce its organic content, so the sahel may be too hot. For fertiliser, rock dust is economically significant.
The program should be quantified:
Available budget for the project.
KG mass of rock:
Quarry cost. Transport cost. Truck+Fuel cost. Crushing machine cost. Energy cost. Dissemination labour organization. Training schemes to instruct dust dissemination. Dissemination machines. Rain window period. Maximium rock load for a given precipitation rate, i.e. 10g/m2 per 1cm of rain.
Using planes to lift 100 tonnes of dust per day may be cheaper than using trucks (a 747 can lift 112 metric tonnes).
Answered by DeltaEnfieldWaid on September 5, 2021
OK I did a paper on mitigating climate change by enhanced weathering of rock on agricultural land for my masters (2014) it's not brilliant, but it does include some useful references if you want to research this further.
I would imagine the main limiting factor in the Sahel region would be that the process needs to be wet. So you're possibly only talking about being able to add material to irrigated areas. There are also the limitations you've already discussed of getting the material on site. In terms of crop yield, I would suggest that it will only increase plant growth in areas which do not already have alkaline geology (and I have no idea what the geology looks like in the Sahel, I'm afraid) and adding too much to soils may well actually decrease site fertility without the addition of something else (manure is the traditional amendment)
As far as I'm aware, enhanced weathering is perfectly technologically feasible, but it does have a limited application - due to the sheer quantity of it we'd need.
Hope this helps.
Answered by Will on September 5, 2021
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