L16- Greenhouse Gas Removal Using Enhanced Weathering

Guest lecture→ David Beerling

• Leverhulme Centre for Climate Change Mitigation→ £10million climate change research institute

• work is focused on taking CO2 out of the atmosphere to mitigate climate change

Past:

• last 100 years→ due to burning fossil fuels, now about 40Gt CO2 released every year

• what we need to do over the next 100 years→

  • transition to clean energy

  • reduce emissions

  • need to take CO2 out of the atmosphere

    • some sectors will be really hard to decarbonise e.g. agriculture and transport

    • need to take it out because there is too much in there

  → need to research now

  

Enhanced Weathering-

• CO2 removal technology

1. maize plants growing in field, add crushed silicate rocks (basalt)- have higher reactive surface areas, react quickly in soil

2. CO2 and H20 in the soil make carbonic acid, wears the rocks, releases bicarbonate ions which is CO2 fixed in a soluble form

3. bicarbonate ions are transferred into the oceans over time

   

• helps reduce ocean acidification→ CO2 dissolves into ocean

• harnesses natural reactions that have been stabilising the climate for millions of years

• is deployable at scale within a decade or two→ know how to mine and apply rocks already

• co-deployable with other CO2 removeable strategies

Literature-

• wrote this out in 2018- outlined that it is CO2 removal but also improves soil health and food security

• had mixed responses to this

Co-benefits of enhanced rock weathering:

• reverse soil acidification→

  • apply lime for pH management for soil to take up nutrients

  • using rocks instead increases yield and capture carbon

• reverse silica stripping→

  • food crops accumulate silica, but take silica off fields when removing crops, reduces ability to defend themselves

  • put down silicate rocks to replenish pool

• replenish other micronutrients→

  • e.g. phosphorus, potassium, molybdenum

  • are critical for crop health

  • reduce use of fertilisers and cost

• improve soil health→

  • stimulate root growth, fungi

→ increases crop production and crop protection

How it works:

• basalt combines with co2 and water→ bicarbonate→ drains into ocean

• managing pH→ improve nutrient uptake→ increases yields

• do due diligence→ check fate of metals in feedstock

  

3 wins of ERW:

• CO2 removal

• mitigation of other GHG emissions e.g. nitrous oxide

• avoid GHG emissions e.g. reducing need for fertilisers reduces amount of phosphorous and potassium used

Benefits of ERW:

• unlimited carbon sequestration capacity

• uses existing technologies

• is synergistic with other land uses

• provides social justice opportunities→ increase value of own land, job opportunities for those losing jobs in fossil fuels

Carbon sequestration of different CDR techniques:

• in 2015, didn’t know how much co2 could be removed or costs with different techniques:

  

• first few years of project→

  • develop numerical modelling tools to understand this

  • apply to individual nations

  • couple models with climate models, including constraints of resources

• advances→

  1. how quickly are rocks used up

  2. how age cohorts are managed

  3. making nitric acid

  4. resource availability

  

UK:

• aim to be net-zero by 2050

• understanding the potential of ERW with UK crops:

  • found that we could meet half of net zero emissions using ERW with UK crops

  • net CO2 removal increases over time→ 8Mt of co2 per year (after accounting for emissions), with current mining rates

  • increasing mining rates→ using 150Mt of rocks takes net CO2 removal to 30-40Mt

  

→ decisions centre around increasing mining industry in the UK→ issues for social scientists

• particle size→ more grinding of rocks require more energy

  • 80% of particles are less than or equal to 20 micrometres in diameter→ grinding rocks to 20 micrometres can get 10Mt removal by 2045 but if you leave them 10x bigger, can still get 10Mt removal a few years later

  

  → leaving them big reduces energy but can still get the same results a few years later

US:

• Biden administration released a long-term strategy report to get US to net-zero but ignored ERW as a strategy

• made simulations to look at what the US could do e.g. states on the East coast currently produce high amounts of basalt, moving this onto US corn belt

  • by 2050, could get between 0.2-0.4Gt of CO2 removal, whilst also improving soils

    

• are there potentials for re-release of CO2 through this?

  • found that there is only 5% leakage, not a huge loss

    

  → could offer 30-60% of their engineered CDR goals

Field sites:

• have set up a global network of field sites:

  

Corn belt trials, US:

• have added this every year since 2017

• grow crops on rotation→ maize- requires high nitrogen fertiliser, soybean- fixes nitrogen and lowers potential of pests

  

• measuring co2 released→

  • measure bicarbonate ions- difficult to do

  • measure how many ions of calcium have been lost from feedstock and use charge balance to work out how many bicarbonate ions have been made

    

  → have found a way to use isotope dilution mass spectrometry

• applying second technique:

  • rates of co2 removal→ can see how noisy soils are, is increasing

    • more rocks, the cumulative CO2 removal increases to 20T per hectare

    

  • increasing number of samples, annual rate of co2 removal stabilises

  

  → can optimise sample strategy in the field

• pH→

  • control- adding fertilisers reduces pH

  • applying basalt- pH increases in soil, similar response with lower depth of soils

    

• yield→

  • increase in yield by 8%, second year no increase, increase in 16% in soy, 12% increase in maize

  • big benefit initially, decays away, is better than liming though

    

  → basalt provides additional nutrients for crop growth

• can see reduction in nitrous oxide in 7/8 years

  

• air quality→

  • reduction in daily average of ozone in the corn belt by doing enhanced weathering at scale

    

    → interesting feedbacks on air quality

  • yield increases of both maize and soybean by reducing future ozone increases:

    

    → non-trivial increases by doing this at scale

• how does increasing CO2 in plants affect weathering:

  • hypotheses→ all show that elevated CO2 would increase mineral weathering

    

  • in the field→ hypotheses are broadly supported: as CO2 goes up, there is a strong feedback on crop production that drives enhanced weathering

    

UK EW Trials:

• funded by UK government

• 4 aims→

  

• arable crops→

  • study site:

    

  • results→

    • applying basalt increases pH

    

    • applying basalt increases higher alkalinity and in ions

      

    • all trace elements show no significant increase after treatment for three years, only exception is molybdenum but disappeared

      

    → crops don’t accumulate heavy metals→ due diligence

    • no increases of any trace metals draining into the water

      

    • earthworms love basalt→ may have digestive enzymes to inject and break down the minerals

      

• lowland pasture→

  • study site:

    

  • collected storm water and measured chemistry to tell about carbon capture→

    • 2/3 storm events always had are higher pH in both 2023 and 2024

      

    • all storm events had higher alkalinity events in both 2023 and 2024

      

    • no increases in trace metals, slight decrease due to indirect pH effects

      

    • CO2 removal→ still in progress

      

• how do they know models are accurate?

  • benchmark against data

  • theory was 30-60Mt of CO2 a year and field results show it is actually 38-48Mt of CO2 a year

    

    → are in the right ballpark

Future-

• 20 commercial companies doing this worldwide

  • concern is are we measuring co2 removal accurately to sell CO2 credits on the markets?

  • is exciting but need to avoid the risk of the bottom→ assuming that CO2 is being removed

  

  • scandal happened with avoiding deforestation e.g. Verra boss stepping down over this

  

• need a range of processes for the monitoring, reporting and verification of CO2

• need numerical models to understand how much CDR we get once the rocks are put down and over time using

• having an app that certifies amount of CDR-

  

  • are currently making this:

    • put in details-

      

    • simulates changes-

      

Conclusion-

• enhanced weathering exploits what human societies have known for centuries- volcanic rocks are very good for farming

  • e.g. extinct volcano in Vietnam

    

  • e.g. mount vesuvius- exploit nutrient rich volcanic rocks

    

Questions-

• basalt is the most abundant rock in the world→ will work best in tropics with high agriculture, high basalt, and perfect climate conditions

• still need to reduce co2 emissions first, but need this research now to figure out which technologies will work