Will Volcanic Dust Soak Up Carbon?

Guest Post by Ian Magness

As a somewhat lapsed geologist, this old chestnut – save the planet by spreading volcanic dust as fertiliser – interests me and I see that, like so many other discredited climate memes, it’s doing the rounds again:

 

 

Sprinkling volcanic dust onto crops boosts yields by up to 20 per cent while pulling carbon dioxide from the atmosphere, scientists have shown.

https://www.telegraph.co.uk/news/2024/03/28/volcanic-dust-crops-soaks-up-carbon-emissions-yield/

 

There is, however, a little twist to this as number of business types have already jumped on the bandwagon to make a quick buck out of gullible, virtue-signalling punters. You only need to look on eBay or Amazon to see bags (all sizes to 25kg) of the stuff being sold. Larger bags seem to cost around 75p per kg – with 1kg apparently enough to treat 2 square metres, presumably for a year but that isn’t specified. So, that’s 37.5p per square meter, probably per year. At a wild guess, industrial quantities might cost a third of that – shall we say 12.5p per square meter but, of course, there would be highly significant costs on top of that, as I shall explain.

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So, what’s not to like? Fertilise your ground and save the planet. Let’s roll this out across the UK to ensure we reach net zero a lot faster! Ignoring the obvious point that CO2 doesn’t actually drive the climate, so this is a fatuous pursuit anyway, let’s humour the project sponsors and analyse it. Points are as follows:

1) The existing dust itself appears to be taken, presumably cheaply, from the waste piles of existing mining and crushing of basalt in the UK.

2) It is claimed that crop yields are boosted by 10% to 20% by the dust.

3) The article states that "It is estimated that if rolled out widely, the process could remove up to 30 million tonnes of carbon dioxide by 2050, representing 45 per cent of the atmospheric carbon removal Britain requires to reach net-zero.

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So far so good. But:

a) Is a yield enhancement of 10% to 20% that great compared to existing fertilisers? If the enhancement was below 20%, would farmers even bother with all of the extra cost? I doubt it. There is no doubt that crushed basalt contains many minerals useful to plants. Then again, chemically complex basalt averages around 50% silica alone, which is completely useless from a plant nutrition perspective. It’s a shame that the study doesn’t specify what % of volcanic dust is useful fertiliser (clearly, significantly less than 50%) and compares that to the % usefulness of present industrial fertilisers. I suspect that modern fertilisers are a lot more efficient by weight and volume – otherwise why waste all those extra costs for manufacture, packaging, transportation and distribution?

b) Government statistics indicate that “croppable” British land covered some 6 million hectares in 2023. 1 hectare is 10,000 square metres. So, the croppable area covers approximately 60 billion square metres. At 1kg per 2 square meters, this requires 30 billion kg of volcanic dust per annum. Yes, that’s 30,000,000,000kg per annum.

c) Under the fantasy scenario revealed in this article, approximately 1.2 million tonnes of CO2 will be removed by this process per annum. I assume they mean metric tonnes, so that’s 1.2 billion kg of CO2. So that’s 30 billion kg of ground spread volcanic dust to reduce “carbon emissions” by 1.2 billion kg a year, of course ignoring those pesky production and distribution “emissions”.

d) What is the estimated impact on global warming of removing this 1.2 million tonnes of CO2? Well, it is estimated that removing 7,800 million tonnes of CO2 would result in a drop in CO2 concentration of 1ppm. But, global mean surface temperature has only risen around 1.5C as a result of c220 more ppm of CO2. So, the temperature difference per 7,800 million tonnes is 1.5/220 = 0.0068C. We, however, are only talking about 1.2 million tonnes, so the annual difference in mean global temperature will be 0.0068 x 1.2/7,800 = 0.000001C. Hmmm, can we even measure that? Would it matter if 100 countries did the same? Maybe not. Oh, and that’s before related emissions from the processes.

e) Looking at the distribution costs in terms of CO2 emissions, let’s do a back-of-the envelope calculation. Let us assume that a large, multi-axle truck can carry 40 tonnes of rock dust. With 30 million tonnes to shift, that’s 750,000 return truck journeys. Let’s assume that the average return journey would be 200 miles. So, that equates to 150 million truck miles per annum. Now, estimates vary but a reasonable figure might be CO2 emissions of 5 metric tonnes per 1,000 miles of travel. The return journey would be a lot lighter, so let’s guestimate 3.5 metric tonnes per 1,000 miles. At 150 million miles, that equates to 525,000 metric tonnes of CO2 emissions. Remember, we are only avoiding 1.2 million tonnes of CO2 in the first place. Even if these heroic estimates are somewhat inaccurate, the truck distribution emissions alone take a sizeable chunk out of the savings. That, of course, ignores the emissions from the mining and crushing processes noted below.

f) It is not clear just how much spare dust our basalt processing industries create per annum but I would assess that the chances of it being 30 billion kg per annum to be approximately zero. In practice, this would mean that a whole new rock mining and processing industry would have to be created to create the dust and, gosh, just think of the carbon emissions that all those men, machines and consumables would generate in crushing all those tons of basalt. And that’s all before the billions of kg of dust is packaged up and transported on journeys across Britain.

g) Most mineable basalt in the UK is found in the so-called Tertiary volcanic district of western Scotland, the Hebrides and the tip of Northern Ireland. There are other possible areas with older basaltic rocks – the Campsie Fells and the Lake District spring to mind – but, again, the bulk are well north of where most "croppable" agricultural land is. There are significant transport and distribution costs in terms of cash and "carbon emissions" resulting from that fact.

To summarise, we are looking at the creation of a new multi-billion £ industry just to make an inefficient fertiliser compared to chemical fertilisers as available to farmers right now. Further, if you add up the "carbon" costs of the mining, processing and distribution resulting from this new heavy industry, and compare that to the "carbon" supposedly to be removed from the atmosphere (and that’s using pretty dubious assumptions), is this scheme even worth considering? It certainly won’t make any discernible difference to the climate that’s for sure.

I don’t doubt that there are good, viable localised scenarios where basaltic dust can be efficiently used by the farming or domestic communities, very especially if the dust is simply a waste product of other industrial processes. When you consider this – as the proponents do – on a national scale, however, the maths just don’t add up either for monetary or CO2 cost. This just seems yet another completely ridiculous scheme to me. The numbers are not hard to find or crunch so, yet again, why didn’t this journalist do the simple maths?

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Paul’s Thoughts

I have one very basic question for those pushing this harebrained scheme:

If it is such a good and cost effective fertiliser, then surely farmers would be using it already?

As they are not, it appears just to be another waste of money, pursuing miniscule savings of carbon emissions, which as Ian Magness points out, probably won’t even exist once the supply chain is taken into account.