GSP Webinar: RECSOIL: Recarbonization of Global Soils, 17 June 2020, Zoom platform. Presentation by Pete Smith, Professor of Soils and Global Change, Aberdeen University and Science Director of Scotland’s ClimateXChange.

1. Is soil organic carbon sequestration really
feasible? How to scale it up?
Pete Smith
Professor of Soils & Global Change, FRS, FRSE, FNA, F.EurASc, FRSB
Institute of Biological & Environmental Sciences
University of Aberdeen,
Scotland, UK.
E-mail: pete.smith@abdn.ac.uk
RECSOIL seminar, FAO, Rome, 7th April 2020

2. Soil organic carbon sequestration is
feasible and the potential is large…

3. Soil C sequestration – global mitigation potentials
Technical potential = 1.3 Gt Ceq/yr
Economic potential at 20-100 US$/tCO2eq = 0.4-0.7 Gt Ceq/yr
Paustian et al. (2016); Smith GCB (2016)

4. Bossio et al. (2020)
Additional SOC storage potential for 12
natural pathways to climate mitigation

5. … and it has range of co-benefits…

6. Beneficial
impacts for
Soil C
sequestration
on ecosystem
services and
the UN SDGs
Smith et al. (2019)

7. … but beware of some limitations…

8. Smith (2008) International Journal of
Agricultural Sustainability 6(3),169–170
• “There are a number of well rehearsed arguments against
reliance on carbon sequestration for tackling climate change,
involving saturation of the carbon sink (the carbon is only
removed from the atmosphere while the tree is growing or
until the soil reaches a new equilibrium soil carbon level;
Smith, 2005), permanence (carbon sinks can be reversed at
any stage by deforestation or poor soil management; Smith,
2005), leakage/displacement (e.g. planting trees in one area
leads to deforestation in another; Intergovernmental Panel on
Climate Change (IPCC), 2000), verification issues (can the sinks
be measured; Smith, 2004), and total effectiveness relative to
emission reduction targets (only a fraction of the reduction
can be achieved through sinks; IPCC, 2007)”.

9. Soil C
Vegetation C
Time since management change
Cstock
Management change
Saturation – the time course of C
sequestration
• Sink saturation ~ 20-100 years
• Sink strength declines towards new equilibrium
Smith (2004a)

10. Permanence
25
35
45
55
65
75
85
1844 1894 1944 1994 2044 2094
Year
TotalSOCto23cm(tCha
-1
)
Management change
Conversion to low-input cropland
Manure treatment in red,
Woodland in blue
Smith (2005)

11. Leakage / displacement: are we actually
sequestering carbon or just moving it about?
Farm with more manure Farm with less manure
Manure Manure Mineral N
More manure here….but……..less manure here
Effect over the whole cropland area = zero

12. …and we can scale it up with suitable
monitoring, reporting and verification

13. Soil Monitoring, Reporting and Verification
Smith et al. (2020)

14. Thank you for your attention