scale, costs etc
19 February 2018  16:00
Guest post: How ‘enhanced weathering’ could slow climate change and boost 
crop yields

*Prof David Beerling 
director of the **Leverhulme Centre for Climate Change Mitigation* 
<>*, and **Prof Stephen Long* 
<>* from the Department of Crop 
Sciences and Plant Biology at the**University of Illinois at 
Urbana–Champaign* <>*.*

Achieving the Paris Agreement 
<> goals 
of keeping global warming to “well below” 2C, or to 1.5C, above 
pre-industrial levels will require rapid decarbonisation of human society.

But national commitments 
<> to 
rein in greenhouse gas emissions are currently insufficient 
meet these agreed limits. It is increasingly likely that “negative 
emissions”, or “carbon dioxide removal”, technologies will be needed to 
take up the slack.

These techniques involve extracting CO2 from the atmosphere and storing it 
indefinitely. Scientists have proposed a range of different approaches 
we now need realistic assessment of these strategies, what they might be 
able to deliver, and what the challenges are.

In a new paper for Nature Plants 
<>, we tackle an 
under-discussed technique of CO2 removal called “enhanced rock weathering”. 
Our research highlights the potential wider benefits for crop yields and 
soil health, and sets out a research agenda for the next steps.
What is enhanced weathering?

As you might remember from geography classes at school, chemical weathering 
is a natural process that continuously erodes away rocks in our landscapes 
and sequesters atmospheric CO2 over millions of years.

The process begins with rain, which is usually slightly acidic having 
absorbed CO2 from the atmosphere on its journey to the ground. The acidic 
rain reacts with the rocks and soils it lands on, gradually breaking them 
down into minute rock grains and forming bicarbonate in the process. 
Eventually, this bicarbonate washes into the oceans, where the carbon is 
stored in dissolve form for hundreds of thousands of years or locked up on 
the sea floor.

Enhanced weathering scales up this process. It involves pulverising 
silicate rocks such as basalt – left over from ancient volcanic eruptions – 
to bypass the slow weathering action. The resulting powder, with a high 
reactive surface area, is then spread on large areas of agricultural land 
where plant roots and microbes in the soil speed up the chemical reactions.

[image: Graphic on 'Advanced weathering'] 

As natural rock weathering absorbs around 3% of global fossil fuel 
emissions, enhanced weathering can provide a boost to remove even more CO2 
from our atmosphere.

But the potential benefits do not end there. As enhanced weathering makes 
water more alkaline, it can help counteract ocean acidification 

And adding minerals to soils can boost nutrient levels 
improving crop yields and helping restore degraded agricultural soils.
Food demand

The need to cut CO2 emissions is unfolding alongside an unprecedented 
increase in food demand – linked to dietary changes and a growing 
population that may surpass 11 billion by 2100 
At the same time, farming itself a growing contributor to climate change 

Critically, enhanced rock weathering works together with existing managed 
croplands.  Unlike other negative emissions techniques under consideration, 
it doesn’t compete for land used to grow food or increase the demand for 

While enhanced weathering can be applied to any soils, arable land is the 
most obvious candidate as it is worked and planted throughout the year. It 
covers some 12m square kilometres – 11% of the global land area.

In fact, arable farms already apply crushed rock in the form of limestone 
to reverse acidification of soils caused by farming practices, such as the 
use of fertilisers. And there is a long history of small-scale farming 
using silicate rocks to improve crop yields in highly-weathered soils in 
Africa, Brazil and Malaysia.

Swapping silicate for limestone, and increasing the application rate, would 
do the same job to help tackle acidification, but help capture CO2 from the 
atmosphere at the same time.

Managed cropland, therefore, has the logistical infrastructure, such as 
road networks, and the machinery needed to undertake this approach at 
scale. These considerations could make enhanced weathering potentially 
straightforward to adopt.

You can see this in action in the video below from the Leverhulme Centre 
for Climate Change Mitigation.

Using silicate rocks as a resource in this way could also have a number of 
important wider benefits. These include supplying silica back into soils to 
improve crop health and protection from pests and diseases, and supplying 
nutrients to increase yields.

If realised, these benefits would reduce the usage of agricultural 
fertilisers and pesticides, lowering the cost of food production, 
increasing the profitability of farms and reducing the barriers to take up 
enhanced weathering for the agricultural sector.
Estimates and challenges

So, in theory, there are a lot of potential upsides for using enhanced 
weathering. However, like many negative emissions technologies, 
implementation is still in its very early stages. It needs further 
research, development and demonstration – not just across a range of crops 
and soil types, but also different climates and spatial scales.

There have been some successful field tests of using enhanced weathering – 
though for purposes other than capturing CO2.

For example, in a 12-year study <> 
in a New Hampshire forest, scientists measured the effect of spreading 
silicate powder as a method of accelerating recovery from acid rain. The 
results confirmed some of the main impacts of enhanced weathering – a rapid 
increase in dissolved silicate and calcium making it into streams, and 
alleviation of acidification in the ecosystem.

Similarly, in Mauritius, sugarcane trials as far back as 1961 added crushed 
basalt to soils and increased yields by 30% over five successive harvests.

There are other challenges too. The process of mining, grinding and 
spreading rocks on a large-scale would likely have negative environmental 
and ecological impacts, and would therefore require careful management. 
Depending on the size of the grains of powder the rocks are pulverized down 
to, the energy demand could account for 10-30% of the amount of CO2 
sequestered. Using renewable energy sources would minimise this.

Costs, too, need to be considered. Current cost estimates are uncertain and 
vary widely. The most detailed analysis to date 
operational costs at $52-480 per tonne of CO2 sequestered – though these 
estimates are poorly constrained and improvements in crop yields and lower 
fertiliser needs will offset some of these costs. This compares with a$39-100 
per tonne of CO2 <> for 
another, more talked-about negative emissions technology, bioenergy with 
carbon capture and storage 

Credit: Dr Ilsa Kantola, University of Illinois, Champaign-Urbana

But the potential is significant. For example, applying 50 tonnes of basalt 
powder per hectare per year to 70m hectares of the corn belt of North 
America might sequester as much as 1.1bn tonnes of CO2 in the long run – 
equivalent to 13% of the global annual emissions from agriculture.

Countries with considerable productive farmland have the largest potential 
to sequester CO2 through enhanced weathering. These include the US, China, 
India and Russia, which all grow crops on a massive scale and make up the 
highest emitters of CO2.

Scaling estimates up to a global level is tricky, but – for example – 
adding 10-30 tonnes of silicate per hectare per year to two-thirds of the 
world’s most productive cropland could take 0.5-4bn tonnes of CO2 out of 
the atmosphere per year by 2100. But current estimates are highly uncertain 
and require more research.
Putting theory into practise

Human societies have long known that volcanic plains are fertile; ideal 
places for growing crops without adverse human health effects but, of 
course, with little consideration for how adding additional rocks to soils 
might capture carbon.

We now need to take the theory and laboratory tests out into real crop 
fields to see how enhanced weathering fits – practically and economically – 
in the wider portfolio of options for removing CO2 from the atmosphere.

However, there is still a long way to go and research in this area remains 
in its infancy.  Improved assessments are required to understand how much 
CO2 the approach would capture, how much rock is required, how much energy 
is required to crush and distribute the rock, and to better understand the 
long-term effects on soils and water courses.

We need to undertake carefully monitored assessments on arable land. For 
example, can we demonstrate the expected benefits to crops amidst the 
seasonal and annual variations in the weather?

And finally, we need to better understand the public perception of enhanced 
rock weathering as a strategy for carbon capture, communicate the process, 
benefits and risks, and understand any public concerns about what this 
means for our landscapes and farmlands.

Beerling, D. J. et al. (2018) Farming with crops and rocks to address 
global climate, food and soil security, Nature Plants, 

On Monday, February 19, 2018 at 6:07:11 PM UTC, Andrew Lockley wrote:
> X-post: it's CDR, in a good journal. CDR list tends to host more ongoing 
> discussion of such papers, but replies are welcome here
> A
> ---------- Forwarded message ----------
> From: "Greg Rau" < <javascript:>>
> Date: 19 Feb 2018 18:02
> Subject: [CDR] Farming with crops and rocks to address global climate, 
> food and soil security | Nature Plants
> To: "Carbon Dioxide Removal" < <javascript:>
> >
> Cc: 
>> “The magnitude of future climate change could be moderated by immediately 
>> reducing the amount of CO2 entering the atmosphere as a result of energy 
>> generation and by adopting strategies that actively remove CO2 from it. 
>> Biogeochemical improvement of soils by adding crushed, fast-reacting 
>> silicate rocks to croplands is one such CO2-removal strategy. This approach 
>> has the potential to improve crop production, increase protection from 
>> pests and diseases, and restore soil fertility and structure. Managed 
>> croplands worldwide are already equipped for frequent rock dust additions 
>> to soils, making rapid adoption at scale feasible, and the potential 
>> benefits could generate financial incentives for widespread adoption in the 
>> agricultural sector. However, there are still obstacles to be surmounted. 
>> Audited field-scale assessments of the efficacy of CO2 capture are urgently 
>> required together with detailed environmental monitoring. A cost-effective 
>> way to meet the rock requirements for CO2 removal must be found, possibly 
>> involving the recycling of silicate waste materials. Finally, issues of 
>> public perception, trust and acceptance must also be addressed.”
>> --
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