The 4 per
mille initiative was launched at COP21, where the Paris Agreement was adopted,
and one of the main aims of the Paris Agreement is to stop the planet from
warming an additional two Celsius degrees.
Two numbers and an optimistic proposition
The amount of carbon that is lost to the
atmosphere as carbon dioxide from fossil fuel emissions alone is estimated at
8.9 Gigatonne (Gt) per year. Scientists estimate the amount of soil organic
carbon (SOC) stock (not concentration) to a depth of 2 m at 2400 Gt. Therefore,
by simple math the annual increase in global SOC stock that could offset the
fossil fuel carbon dioxide emissions would be 8.9/2400 or approximately 4 per
1000 (mille). Minasny and a panel of scientists engaged at the 21st
Conference Of the Parties (or COP2, Paris Agreement 2015) to the United
Nationals Framework Convention on Climate Change Agreement proposed this
concept of “4 per mille soils for Food Security and Climate” in 2017.
The aim of the initiative is to promote land
management practices leading to an increase in the SOC stock at the rate of
0.4% of the initial value per year for 20 years. It was proposed that if this
rate was achieved for all soils globally to a depth of 40 cm, it could effectively
offset global anthropogenic greenhouse gas emissions by 35%.
Criticisms and a riposte
4permille has been received by the broader
scientific community as an overt optimism (De Vries, 2017; White et al, 2017). Among
the prominent criticisms are an assumption that soil carbon stock can increase
indefinitely, the lack of accounting for response of altered land management on
the carbon dioxide equivalent (CO2-e) of other major greenhouse gas
productions like methane and nitrous oxide, and the absence of a plan for
economically incentivizing farmers to adopt to new practices. Newer practices
proposed are addition of farmyard manure, adoption of no-till and conservation
practices in agricultural fields.
Recent literature Lal (2016)
states that the technical potential of SOC sequestration in the world's
cropland and grazing lands is finite: 0.4 to 1.2 Gt C yr−1 for
cropland, 0.3 to 0.5 Gt C yr−1 for grazing lands, and 0.5 to 1.4 Gt
C yr−1 for restored degraded soils. Results from a long-term study
provided empirical evidence that SOC stocks increased between 0 and 0.1% after
20-157 years of diverse management practices for carbon sequestration (Poulton
et al., 2018). And, the true abatement of greenhouse gas emission is likely
to be deficient in cases where land is converted to pasture due to methane
emissions from the grazing animals. Methane is a much more potent greenhouse
gas, ~25 times stronger than carbon dioxide in its global warming potential.
Currently, there is no tradable value for soil
carbon as a commodity. Financial incentives are limited to taxpayer subsidies
through government interventions as currently practiced in Australia and the
state of California in the United States: currently
USD 3.3 per tonne CO2-e in the voluntary international carbon market
(Hamrick and Goldstein, 2016) or less than USD10 per tonne CO2-e
for 75% of global emissions under government mandated schemes (World Bank, 2016).
Promise
of the future
The economic reality and the truth is
that the world needs resources to feed a population of over 9 billion people by
2050. Recently, a new
agricultural bill has been introduced in the UK’s parliament mandating
preservation and improvement of the nation’s soil health in light of the
estimated 60 harvests left. Based on current knowledge, the
science behind SOC sequestration is somewhat factious. But, the scientific community concurs that strategies
to mitigate climate change must include radical land use change coupled with enhanced carbon sequestration
technology. Acceleration in concerted efforts are needed to precisely quantify
the benefits of SOC increase on soil productivity and resilience, so that a
monetary value can be attributed to SOC. Another area in which science can make
a significant impact is in better methods of measuring SOC change in the field and
in identifying spatially-resolved areas where the most significant changes in
SOC are likely to be achieved, globally.
As
Milasny et al. (2018) state in their rejoinder, 4 per mille is ‘the right
and honest way to help persuade land managers, policy-makers and society of the
importance of soil for climate and food security, engaging farmers, scientists,
and marketers’.
References:
De
Vries, W. 2017. Soil carbon 4 per mille: a good initiative but let’s manage not
only the soil but also the expectations. Geoderma, 309: 111-112.
Hamrick,
K., and Goldstein, A. 2016. Raising Ambition: State of the Voluntary Carbon
Markets 2016. Washington, DC: Ecosystem Marketplace. Retrieved from
http://www.greenresources.no/Portals/1/Articales/StateoftheVoluntaryCarbonMarket18July_Final.pdf
Lal,
R. 2016. Beyond COP 21: potential and challenges of the “4 per Thousand”
initiative. J. Soil Water Conserv. 71, 20A–25A.
Minasny,
B., Malone, B.P., McBratney, A.B., Angers, D.A., Arrouays, D., Chambers, A.,
Chaplot, V., Chen, Z.S., Cheng, K., Das, B.S., Field, D.J., Gimona, A., Hedley,
C.B., Hong, S.Y., Mandal, B., Marchant, B.P., Martin, M., McConkey, B.G.,
Mulder, V.L., O'Rourke, S., Richer-de-Forges, A.C., Odeh, I., Padarian, J.,
Paustian, K., Pan, G., Poggio, L., Savin, I., Stolbovoy, V., Stockmann, U.,
Sulaeman, Y., Tsui, C.-C., Vågen, T.-G., van Wesemael, B., Winowiecki, L.,
2017. Soil carbon 4 per mille. Geoderma 292, 59–86.
Minasny,
B., Arrouays, D., McBratney, A. B., Angers, D. A., Chambers, A., Chaplot, V., …
Winowiecki, L. 2018. Rejoinder to Comments on Minasny et al., 2017 Soil carbon
4 per mille. In press.
Poulton,
P., Johnston, J., Macdonald, A., White, R., Powlson, D. 2017. Major limitations
to achieving “4 per 1000” increase in soil organic carbon stock in temperate
regions: evidence from long-term experiments at Rothamsted Research, United
Kingdom. Global Change Biology, 2018:1–22
White, R.E., Davidson, B., Lam, S.K., Chen, D. 2018. A critique of the
paper ‘Soil carbon 4 per mille’ by Minasny et al. (2017). Geoderma, 309, 115-117.
World Bank. 2016. Climate change action plan 2016-2020.
