scale, costs etc
GUEST POSTS <https://www.carbonbrief.org/category/in-focus/guest-posts>
19 February 2018 16:00
Guest post: How ‘enhanced weathering’ could slow climate change and boost
*Prof David Beerling
director of the **Leverhulme Centre for Climate Change Mitigation*
<http://lc3m.org/>*, and **Prof Stephen Long*
<https://lab.igb.illinois.edu/long/team/long/>* from the Department of Crop
Sciences and Plant Biology at the**University of Illinois at
Achieving the Paris Agreement
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
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
<http://nature.com/articles/doi:10.1038/s41477-018-0108-y>, 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.
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 <http://www.publish.csiro.au/en/EN15113>
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 <https://www.nature.com/articles/nclimate2870> 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
> ---------- Forwarded message ----------
> Date: 19 Feb 2018 18:02
> Subject: [CDR] Farming with crops and rocks to address global climate,
> food and soil security | Nature Plants
>> “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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