The document provides an overview of what is known about carbon storage and sequestration in various UK terrestrial habitats. It notes that the evidence base is still developing and varies in certainty between habitat types. Key points made include: - Woodlands and peatlands store the most carbon, primarily in soils. New woodland creation and restoration of degraded habitats can sequester carbon. - Grasslands are also significant carbon stores, though intensive management may reduce soil carbon. Reducing grazing and soil disturbance helps sequestration. - Heathlands store carbon in soils, especially wet heathlands. Management practices should minimize soil disturbance to avoid carbon emissions. - Further research is still needed to better quantify carbon metrics

1. The role of terrestrial habitats in carbon
storage and sequestration in the UK
A look at the literature
Julie Middleton and Tony Whitbread
For Sussex Local Nature Partnership Carbon workshop
March 2020

2. Habitats and carbon – what we know
• Habitats are ‘stores’ of carbon. The amount they store (per ha) depends on
the habitat type and, in most cases, its condition.
• For most habitats, the majority of carbon stored is held in the soil –
although the role of above and below ground biomass is also important
(e.g. woodland).
• Destruction and/or degradation of habitats tends to result in the release of
carbon into the atmosphere.
• Restoration/management of habitats to improve their condition - tends to
increase the amount of carbon they actively remove from the atmosphere
(sequestration – measured in tonnes C (or C02 equivalent) per ha per year)
• For wetlands, the complication is that restoration/re-wetting can result in
emission of methane
• So- the ‘flux’ of greenhouse gases between habitats and the atmosphere is
complex and depends on many factors

3. Developing natural climate solutions – the information we need
If we are to:
a) adequately protect existing habitats as ‘natural carbon stores’ - from
loss/degradation
b) Encourage investment in habitats as effective carbon sequestration assets
c) Manage the habitats in our care with a conscious understanding of how this
affects their role in carbon storage and sequestration
…we need to understand several things:
• How much carbon is stored by each habitat type (tC per ha)?
• How much carbon new/restored habitats can sequester from the atmosphere (t C
per ha per year – for each habitat type)?
• How our management of a habitat affects this carbon sequestration rate?

4. So where is the problem….
• The science/research in this area is ‘patchy’ i.e. we know the answers to these
questions better for some habitats than others i.e. there is reasonable certainty
and confidence in the evidence for some habitats – and less for others
• For many habitats/types of land-use, there is a wide range of estimates of the
Green House Gas(GHG) flux per unit area in the literature. Often we just have to
chose the ‘median’ value – within a large range of values. This could make us
very far off the mark in terms of what the habitats are doing in practice!
• The evidence base is rapidly evolving
• There is no ‘one-stop-shop’ review of the science that provides the carbon
metrics for each habitat that can be directly applied to project development
• This makes life very difficult for those seeking to ‘evidence’ the role of habitats in
carbon storage and for those developing an ‘offsetting offer’ based on local
habitats.

5. This presentation….
• We set out our understanding of what we know so far – for a range of
habitats found in Sussex
• We can signpost you as we go along – to the core pieces of research
currently being used to develop metrics
• Caveat: we are not quantitative ecologists/scientists – so this is our
basic understanding of the evidence we have found. But we hope it is
a start

6. Questions to bear in mind…
• Is there a clear understanding of how different habitats store and sequester
carbon – and the rates at which they do so?
• Is the evidence base relevant to the south–east UK context we are working
in?
• Do we understand how management practices will change carbon storage
and sequestration?
• How will the sequestration by a habitat change through time? What factors
might affect this (e.g. climate change, pressures on habitats etc)?
• Can we measure (or estimate with confidence) the carbon that will be stored
and actively sequestered?
• Ultimately – can we be confident that a project will ‘do what we say it will’ in
terms of storing carbon through time?
• Why? Reliability and reputation of the project - and ‘investor confidence’ will
depend on this

7. Key terrestrial habitats for carbon storage and
sequestration – present in Sussex:
• Woodland
• Grasslands
• Hedges
• Heathland
• Wetland
• What does the literature say about carbon storage, sequestration and
impact of management on these? Are there any ‘metrics’ for each we can
use for practical application?

8. A word on units of measurement….
Carbon storage is expressed as tonnes C per hectare of habitat
Carbon sequestration is expressed as tonnes C per hectare per year
But - sometimes mass of CO2 equivalent is used!
Important to notice which is being used. Make sure you are comparing
like with like!
• Conversion of carbon units into CO2 units: multiply by 3.66667

9. How much carbon do habitats store?
Natural England (2012). Research report NERR043
http://publications.naturalengland.org.uk/publication/1412347
*Woodland: highest total
vegetation + soil
Units: Tonnes of carbon per hectare
Carbon stores for most
habitats are in the soils!
This is the key government
publication of evidence in this
area to date. NE have told us
it will be updated in a couple
of months!

10. Land Use Type Vegetation carbon stock (MgC
ha-1)
Soil Carbon Stocks (MgC ha-1)
Average Min Max Average Min Max
BL Forest 111 57.4 208 162 70.5 335
Complex Cultivation patterns, fruit
trees and. Berry plantations, land
principally occupied by agriculture,
with significant areas of natural
vegetation; transitional woodland-
shrub
14.7 2.0 36.7 88.4 37.5 120
Coniferous Forest 59.1 26.7 95.8 107 81.9 175
Green Urban Areas, sport and leisure
facilities
8.32 2.0 25.1 91.3 40.0 142
Inland and salt marshes 8.44 1.0 15.0 143 38.4 235
Mixed forest 78.0 47.5 139.0 124 85.6 179
Moors and heathland 7.11 2.0 17.5 103 50.7 196
Natural Grasslands; pastures 3.1 1.0 6.98 121 72.0 204
Non-irrigated arable land 2.36 1.0 4.64 63.9 27.5 88.2
Bioenergy crops 2.9 1.56 4.47 74.6 69.8 80.2
Peat Bogs 7.15 1.57 20.0 576 133 1170
Cantarello, E., Newton, A.C., and Hill, R.A. (2011). Potential effects of future land use change on
regional carbon stocks in the UK. Environmental Science and Policy 14 (40-52).
http://trees-for-transition.co.uk/cantarellocarbon.pdf
Earlier but important piece of work
Peat – the ’soil’ top
performer
Other good soil stores
– grassland, woodland.
Inland and
saltmarshes

11. Other useful sources:
• RSPB Accounting for Nature. This document – also reviews the literature to
identify metrics for the emissions of Green houses gases from habitats.
See section 7.2.1. in annexes
https://www.rspb.org.uk/globalassets/downloads/documents/positions/eco
nomics/annexes-to-accounting-for-nature---a-natural-capital-account-for-
the-rspbs-estate-in-england.pdf
Some of the metrics they identified are set out in this presentation.
ENCA Services datebook.
Produced by ONS, this contains spreadsheets which are based on key metrics
from literature. See https://data.gov.uk/dataset/3930b9ca-26c3-489f-900f-
6b9eec2602c6/enabling-a-natural-capital-approach
This contains a list of sources – under the ‘carbon reduction’ tab

12. Woodlands: carbon storage
Key reference/body of work – FC Woodland Carbon Code.
https://www.woodlandcarboncode.org.uk/
See FC presentation for how this works!
Notes on woodland and carbon storage.
• Storage in biomass (above ground and below ground) – is what makes woodland stand out from
other habitat types!
• But - in woodland, remember that a significant % of the total carbon is in the soils (see previous
tables)
• Carbon losses from the soil caused by disturbance can take decades, even centuries, to make up.
• Previous land use is the most important factor in determining effect of afforestation on net carbon
impact
• e.g. change from cultivated soil to forest is likely to be carbon positive, but carbon stocks in
grassland are already high so there is less opportunity for additional carbon capture on these soils
• Planting on peatland/ or peat rich soils is not advisable – drained peatland will release CO2

13. New woodland creation
• Young/ newly planted trees take time to ramp up their sequestration rates (up
to10 years)
• Carbon rates increase with growth rates, before slowing down as trees reach
maturity
• ‘Peak’ sequestration rate at around 100 years (but opinions on this differ!)
• 0.1ha land needed per tC02 pa over 100 years
• Shallow rooted conifers store carbon in the more easily disturbed surface layers.
Deeper rooted species (e.g. beech) store carbon in the deeper mineral soils aiding
long term sequestration
• Soil carbon increases after planting broadleaved trees (up to 25% in one study) on
agricultural soils, but planting conifers had little effect on soil organic carbon
• Naturally regenerated forests can lock up carbon relatively quickly, but most
scientific evidence comes from tropical areas. More evidence is needed for the
temperate zone.
• Trees only lock up carbon in the long-term if they are kept in the ground! Making
this happen is an important part of any strategy.

14. Broadmeadow, M. 2003. Forests, carbon and climate change: the UK contribution. Forestry
Commission Information Note. June 2003.
Carbon accumulation in woodland over time (in biomass)

15. The role of woodland management
Woodland Carbon stocks
T CO2 p. ha
Carbon sequestration
T CO2 p. ha p.a.
Unmanaged forest 800 6
Close to nature forestry 500 11
Combined objective forestry 450 16
Intensive even aged 400 22
Biomass 200 29
The choice of management options and species has a significant impact on the
potential of a woodland to store carbon
Taken from Alonso et al 2012. (NERR 043, Natural
England 2012)

16. Woodland Project development/design…..
• Forestry Commission Woodland Carbon Code – this is the voluntary standard for
UK woodland creation projects where claims are made about the carbon dioxide
they sequester.
https://www.woodlandcarboncode.org.uk/
• See other presentation for explanation of how this works.
• Does contain calculation tool for baseline, soil and sequestration to be achieved
from creation of new woodland (not management of existing woodland)
• More certainty around woodland creation metrics than other habitat types – but
still tricky to calculate

17. Grasslands: carbon storage
• Grasslands have high carbon stocks – mostly in the soils.
• Grassland soils have the highest carbon stock of any UK broad habitat type
• Semi-natural and semi-improved grasslands are important carbon stocks – due to
‘permanence’ and lack of soil disturbance over time
• Little literature on relative carbon storage by grassland type (calcareous, acid, neutral)
• Land use change from grassland to arable land releases a significant amount of carbon to
the atmosphere (between 1990 – 2006 = 14.26 Mtonnes C). The reverse is also true
(conversion of cropland to permanent grassland increases soil carbon)
• Factors that negatively affect the carbon stock:
• Destruction (through land use change (as above), loss to development)
• Soil disturbance – in general this releases carbon
• Intensive management (improvement and over-grazing alter soil properties)
• Improved grasslands (regularly fertilized and/or ploughed/reseeded) have different soil
properties from semi-natural and semi-improved grasslands.
• Soil carbon stocks (measured to 1m depth) under intensively managed grassland are
significantly lower than intermediately and extensively managed grassland.

18. Carbon sequestration by grasslands
• Grassland of all types are significant carbon stores – but their ability to actively sequester carbon
(and the rate at which this takes place) depends to a large degree on management activities and
the intensity of management (fertiliser application, irrigation and livestock grazing intensity)
• Intensively managed grasslands (high fertilizer application; high grazing densities) may not be
storing carbon at all in their soils. Do not assume that all grassland is actively storing carbon!
• There is little information as to rates of sequestration in different grassland types (acid, neutral ,
calcareous)
• See table for some info on impact of land use change (NERR 043 Alonso et al 2012)
t CO2 p.ha p.a.
emitted
comments
Grassland
Restored from other land use or improved
grassland
-11.62 Minus is good!
Grazed -2.20
Grassland to arable +3.48 plus
Grassland to afforestation -0.37
Grassland to wetland Up to -14
Restored unimproved grassland (first year) -6.9
(Later years) -4.3

19. Grassland management options for carbon
Literature is limited - but a few generalized comments can be
made:
• Reducing grazing pressure in overgrazed systems seems to increase carbon
sequestration, particularly in wetter systems
• Intermediate levels of management intensity seems to be most beneficial for
grassland soil carbon. Extensive management may actually reduce soil carbon
accumulation over time as plant productivity reduces in response to nutrient
limitation.
• Scrub control and cutting/mowing may have the opposite effect
• In all cases – the highest risks of carbon emissions are from soil disturbance rather
than changes to vegetation structure. Minimising soil disturbance/erosion in
grasslands is therefore important

20. Grassland management options for carbon
• Soil compaction – is limiting factor on the accumulation of soil organic carbon
• Drainage of lowland meadows and Molinia –Juncus pastures results in carbon
losses as a result of oxidation of the organic matter
• Restoring grassland from other land use types or improved grassland does
sequester carbon; restoration of unimproved grassland also does.
• But the literature is limited on rates of carbon sequestration due to restoration or
changing management practices.
• See Alonso et al (2012). NERR 043 for more information on the above

21. Heathland: carbon storage
Key points
• Data set out in NERR 043* – shows huge variations and more information/research is
needed to provide better guidance
• Carbon storage by heathland – only ‘roughly’ estimated and varies across sub-types.
Wet heath on peaty soils – more significant stores than drier heaths on sandy/mineral
soils or dunes.
• Most of the carbon stock associated with heaths is in the soil: carbon concentrations in
heathland soils can be greater than in forest soils.
• Sequestration rates depend on growth stage of vegetation. Bare ground stage may be a
net source; building and mature stages are net sinks and there is no net sequestration in
later stages.
• Danish research used by the RSPB in its Accounting for Nature document (Beier et al
2009) adds another data source for carbon storage by lowland heath:
• Lowland dry heathland, lowland acid grassland & bracken: -1.14 tonnes eC02 per ha per year. (median value)
• Lowland wet and humid heath on peaty podzols: -1.26 tonnes eC02 per ha per year (median value)
*Alonso et al (2012). Natural England Research Report 043

22. Heathland: management options carbon
• Carbon emissions can result from soil disturbance, from damage or even from
management and restoration practices which remove or invert soil. Minimising
disturbance to soil when managing is therefore key. Carbon impacts should be factored
in to choice of restoration practices chosen.
• Role of fire in management – important. For example, fast fires can be carbon neutral,
even positive. Hot burns, however, may release carbon from the organic matter in the
soil
• Calculations have been made for different land use/management choices (for HLS – and
set out in Alonso et al 2012):
• Creating heathland from arable: net sequestration of carbon (-5.44 tC02-eha-1yr-1)
• Maintenance has negligible effect on fluxes of carbon (-0.07 tC02-eha-1yr-1)
• Restoration from neglect: slight emission of carbon (+2.56 tC02-eha-1yr-1)
• Restoration from forestry: changed the system from net sequestration to slight emission (+4.46
tC02-eha-1yr-1)
• See table below for more information – but remember problems noted above for
this habitat type and that data relies on single studies in many cases.
(Alonso et al, 2012. NERR 043)

23. Carbon consequences of management options
Alonso, I., Weston, K., Gregg, R. and Morecroft, M. (2012). Carbon storage by habitat: Review of the evidence of the impacts of management decisions
and condition of carbon stores and sources. Natural England Research Report NERR043. http://publications.naturalengland.org.uk/publication/1412347

24. Hedgerows
Very little scientific study (in UK or elsewhere) and more needed.
Not included in the NERR 043 report (Alonso et al 2012)
One research programme by Royal Agricultural University (M. Axe) provides some data.
Findings include:
• Carbon storage in hedges is found in above ground biomass; below ground biomass and soil
• How hedges are managed is key.
• Increasing the height (to 3.5m) and in particular the width of hedgerows (to 2m) is effective in raising carbon
stored in biomass and soil.
Resulting carbon stores:
• Above Ground biomass for 3.5m hedges = 4.2 +/- 3.78 t C ha-1
• Below ground stocks of 38.2 =/- 3.66 tCha-1 almost equaled that for AGB
Sequestration:
• Newly planted hedges sequester +1tCha-1yr-1 for 5 years
• Soil carbon storage +1.23 % yr-1 until equilibrium
• Species mix? How does this play a role? Need to look for literature on this.

25. Wetlands
• Wetlands cover a broad range of habitats and landscapes, and care must be taken
when comparing carbon storage across them.
• Carbon sequestration is most significant in wetlands characterized by
hydrophytes, and conditions are saturated for much of the year resulting in
formation of peat.
• The research focus has been on peat soils due to their high carbon stores and
potential for peat restoration to capture carbon at high rates
• Much less evidence for other wetlands types in UK
• RSPB Accounting for Nature – references some metrics which may be of use – see
following slide

26. Wetlands as carbon stores
Figures from RSPB (2017) – where ‘-’ is carbon sequestration and ‘+’ is carbon emission
Wetland type GHG flux (tonnes of C02 equivalent per
ha per year)
Source
Swamp and Fen -3.91 (median)
Range -7.91 - +0.1
Evans et al (2016)
Existing wet grassland on organic soils.
(For areas below 300m with high water
table and on peat soils)
-6.05 Based on figures taken from
Lloyd (2006) and Levy (2012)
Re-wetted wet grassland on organic soils
(on previous arable land)
+12.60 (median)
Range +4.92 to +20.27
Evans et al (2016)
Wet grassland on mineral soils -1.55 (median)
Range -2.42 to -0.68
From Allard et al (2007)
Not aware of any measurements
of lowland wet grassland mineral
soils; emissions of methane likely
to be negligible because of low
quantity of organic matter
Open Water: Eutrophic/mesotrophic +6.86 (median)
Range +6.07 - +7.65
From Casper et al (2000), Stets
et al (2009) and Finlay et al
(2010)
Oligotrophic +3.94
(range +3.07 - +4.8)
From Casper et al (2000) and
Finlay et al (2010)

27. Illustration of difficulty in comparing sources….
Wetland (summary NERR 043)
Carbon stock
MT C
Carbon sequestration
Wetlands
Peatlands 584 0.2–0.5 T CO2 p. ha p.a.
Fen, marsh, swamp soils (top 15cm of soil) 76 T C p. ha
Bog soils (top 15cm of soil) 74 T C p. ha
Bog soils (top 50cm of soil) 259 T C p. ha
Lowland fen changed to improved grass 20.58 emitted
Lowland fen changed to forest 2.49 emitted
Different units!?
Are these equivalent figures?

28. Wetland destruction and restoration
Key points about wetlands and carbon….
• Land use change from wetlands to other habitat tends to result in net carbon loss (emission)
• Drainage and disturbance causes changes to carbon cycling, decomposition and fluxes
• Damaged wetlands can be restored – and this does increase carbon sequestration
• This does not compensate for net accumulation of carbon in original system before disturbance
• Thus wetland protection is preferential to restoration
Confidence in metrics – low:
• Wetlands act as ‘transitions’ between terrestrial and aquatic systems.
• Understanding carbon ‘fluxes’ – very difficult
• Much more research needed to understand carbon balance of England’s varied wetland habitats
[Source Alonso et al 2012, NERR 043]

29. Conclusions: key messages
• Woodland – greatest certainty around metrics for habitat creation. Carbon Code
in place to confirm and register carbon outputs from new woodland projects.
Similar code exists for peatland – but not as relevant to SE England context.
Existing storage in woodland biomass and soil carbon is significant – and should
be a priority to protect this. No metrics for woodland
management/improvement? Natural regeneration potential for sequestration
needs specific UK research.
• Grassland – relatively good information on carbon stored by existing unimproved/
semi-natural habitats (although not by sub-type). Protection of these is therefore
key. Less knowledge/no reliable metrics for sequestration from grassland
creation or management of existing grassland (although move to less intensive
management is beneficial). More study required?
• Hedgerows - very little UK study of carbon storage role – although has great
potential given soil and below-ground biomass storage. Some sequestration
calculations done from limited study in UK – so apply with great care. Total
storage can be enhanced with management (wider/higher) – so real scope for
developing beneficial management practice. More study required to develop
metrics.

30. Conclusions: key messages
• Heathland. Huge variation in data – so little certainty on metrics. Minimising disturbance
to heathland soils when managing/restoring is key. Types of management practice and
fire used is thus key. Some HLS figures available for habitat creation/restoration but use
with care. In some cases, restoration may result in net emissions so need to balance this
with other objectives. More research needed.
• Wetland. The term wetland tends to be applied to large number of sub–habitat types
which includes peatlands and fens, which are significant stores of carbon. So use general
figures with care if applying to other types of freshwater sites/non peatlands. NE
acknowledge that much more differentiation is needed between wetland types in
England and their contribution to carbon balance. High levels of uncertainty around
sequestration that can be achieved by management or creation of wetlands in England.
e.g. wetland restoration (estimated 0.1- 1.0 tC ha-1 yr-1) or re-vegetation from
arable/grassland (estimated 0.8-3.9 tC ha-1 yr-1) . Treat these figures with care. In general,
land use change from wetland to other land use type results in net emission of carbon
that cannot be compensated for by later restoration. Protection of existing wetlands is
therefore preferable to restoration.

31. Conclusions (cont)
• For the project developer/investor – navigating this literature to
understand which ‘metrics’ are the most appropriate/accurate for
application in practice is very difficult.
• Often ‘median’ values have to be used from a wide range of values and
there is little accompanying ‘confidence level’ for the values used
• Our recommendation is that it would be very helpful to have a scientifically
agreed set of metrics for use in ‘natural carbon solutions’ so that all
practitioners and investors understand that they are using the ‘best
available’ science from the literature.
• We will approach Defra with this suggestion as part of wider South East
LNP network
• Is there anything else LNPs can do now?
• Questions?

32. Key references
Alonso, I., Weston, K., Gregg, R. and Morecroft, M. (2012). Carbon storage by habitat: Review of the evidence of the impacts of management decisions and
condition of carbon stores and sources. Natural England Research Report NERR043.
Axe, M. (undated presentation). Utilising hedgerows for landscape scale carbon sequestration. Royal Agricultural University, Cirencester. Downloaded from
https://www.agroforestry.ac.uk/sites/www.agroforestry.ac.uk/files/Axe%20Utilising%20hedgerows%20for%20landscape%20scale%20carbon%20sequestration
%20final%20v2.pdf
Axe, M.S., Grange, I.D. and Conway, J.S (2017). Carbon Storage in hedge biomass - a case study of actively managed hedges in England. Agriculture, Ecosystems
and Environment. Vol 250 (1). P81-88.
Beier, C., Emmett, B.A., Tietema, A., Schmidt, I.K., Peñuelas, J., Láng, E.K., Duce, P., De Angelis, P., Gorissen, A., Estiarte, M., de Dato, G.D., Sowerby, A., Kröel-
Dulay, G., LelleiKovács, E., Kull, O., Mand, P., Petersen, H., Gjelstrup, P., & Spano, D. 2009. Carbon and nitrogen balances for six shrublands across Europe. Global
Biogeochemical Cycles 23: GB4008, doi:10.1029/2008GB003381. . In RSPB (2017) Annexes to Accounting for Nature: A Natural Capital Account for the RSPB’s
estate in England. https://www.rspb.org.uk/globalassets/downloads/documents/positions/economics/annexes-to-accounting-for-nature---a-natural-capital-
account-for-the-rspbs-estate-in-england.pdf
Broadmeadow, M. 2003. Forests, carbon and climate change: the UK contribution. Forestry Commission Information Note. June 2003Cantarello, E., Newton,
A.C., and Hill, R.A. (2011). Potential effects of future land use change on regional carbon stocks in the UK. Environmental Science and Policy 14 (40-52).
Climate Exchange (Scotland). Workshop on carbon sequestration in grassland (2013). Downloaded from
https://www.climatexchange.org.uk/media/1839/cxc_workshop_on_carbon_sequestration_in_grassland_7_nov_2013_notes.pdf
Hornigold, K. and Bavin, S. (2019). The role of trees and woods in carbon sequestration and carbon balance. Literature Review (Unpublished, Woodland Trust)
Morecroft, M.D., Duffiend, S., Hartley, M., Pearce-Higgins, J.W., Stevens, N., Watts, O., Whitaker, J. (2019). Measuring the success of climate change
adaptation and mitigation in terrestrial ecosystems. Science 366, 1329.
Janet Moxley, Steve Anthony, Khadiza Begum, Anne Bhogal, Sarah Buckingham, Peter Christie, Arindam Datta, Ulrike Dragosits, Nuala Fitton, Alex Higgins,
Vasileios Myrgiotis, Matthias Kuhnert, Scott Laidlaw, Heath Malcolm, Bob Rees, Pete Smith, Sam Tomlinson, Kairsty Topp, John Watterson, J. Webb,
Jagadeesh Yeluripati. (2014). Capturing Cropland and Grassland Management Impacts on Soil Carbon in the UK LULUCF Inventory. Contract Report prepared for
the Department for Environment, Food and Rural Affairs. Defra Project Code: SP1113 CEH Project Code: NEC04909
RSPB (2017) Annexes to Accounting for Nature: A Natural Capital Account for the RSPB’s estate in England.
https://www.rspb.org.uk/globalassets/downloads/documents/positions/economics/annexes-to-accounting-for-nature---a-natural-capital-account-for-the-
rspbs-estate-in-england.pdf
Royal Society and Royal Academy of Engineering (2018). Greenhouse Gas Removal. royalsociety.org/greenhouse-gas-removal
raeng.org.uk/greenhousegasremoval