Some readers pointed out there are critiques to the Soil Carbon 4 per mille initiative, and especially our paper published in Geoderma (2017). We have responded to those critiques with a rejoinder, especially the tabloid-style writing by Baveye et al.
There’s also a headline “Soil cannot halt climate change” which is a rhetoric, in fact nothing can halt climate change!
Here is just a recap of our response, in case you haven’t read it.
Most of the commentators agree that soil organic carbon (SOC) sequestration is important for improving the quality of soil, however they argue that we have overstated the potential of soil carbon sequestration. We welcome the comments and appreciate that the issue of SOC sequestration has always been somewhat factious.
We clarify that our paper (Minasny et al., 2017) mainly deals with potentials for the 20 countries and regions, where SOC sequestration can also be seen as a way to improving the resilience of the soil to future climate change, that is, improving adaptation rather than mitigation. We believe that in some parts of the world where food security is threatened, the benefit of soil carbon management for adaptation should be stressed more than for mitigation. This is the reason why the 4 per mille initiative explicitly includes food security.
The “4 per mille Soils for Food Security and Climate” initiative is just one of many national and global initiatives on SOC sequestration for mitigating climate change. The Intergovernmental Technical Panel on Soils (ITPS) of the Global Soil Partnership (GSP) discussed incorporating the topic of SOC in the IPCC Assessment Report (ARs), from AR6 onwards. The IPCC has also put a focus on soil in their upcoming special report “Climate Change and Land” (http://www.ipcc.ch/report/sr2/). The recent FAO Global Symposium (GSOC17) assembled experts engaged in FAO, GSP and its ITPS, IPCC, UNCCD-SPI and WMO activities to work together for the common goal of appropriate SOC management as part of overall sustainable soil management within the climate change mitigation and adaptation, sustainable development, Land Degradation Neutrality (LDN) and food security agendas (http://www.fao.org/about/meetings/soil-organic-carbon-symposium/en/). The Global Research Alliance on Agricultural Greenhouse Gases (GRA) focused on opportunities to reduce agricultural greenhouse gas emissions and increase soil carbon sequestration while still helping to meet food security objectives (http://globalresearchalliance.org/about/). The Common Agriculture Policy in the EU is currently being revised to include the potential use of SOC as an indicator.
For the antagonists, do we need to attack and disagree with them all?
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. The two-degree target, although suggested by scientists through modelling work, was chosen more for political and pragmatic reasons.
This is beautifully captured by David Titley:
“Perhaps the most powerful aspect about the 2°C threshold is not its scientific veracity, but its simplicity as an organizing principle.”
The 4 per mille initiative comes from a politically-driven aspiration, and our paper is a response to such an aspiration, to seek and outline possibilities based on current knowledge. The important concept is that soil and agriculture are part of the solution, and it is an interim and evidence-based solution that we can implement.
Baveye et al. consider the 4 per mille initiative as a ‘credibility issue for the science community’ and we fully understand their point of view, but we do not share it.
Baveye et al. said: “The idea, based on back-of-the-envelope calculations is deceptively simple…”. Baveye and others in the scientific community, might not be aware of the scientific discussions that took place before and during the launching of this programme (http://newsroom.unfccc.int/lpaa/agriculture/join-the-41000-initiative-soils-for-food-security-and-climate/ ), and especially that the 4 per mille initiative will include a proposal for a research programme, and that it will be guided by a scientific committee (http://www.agropolis.fr/pdf/actu/4-per-1000-comite.pdf). Discussions about the 4 per mille initiative have taken place under the auspices of the International Union of Soil Sciences (IUSS) representing the global union of soil science societies.
Baveye et al. have adopted a polemical-tabloid style and multi-faceted approach for their commentary to which we respond in a collegial spirit with a view to making concerned scientists aware of the situation. The research community has provided insights to the 4 per mille concept. Simple ideas may appear deceptive to some, but our view is that arguing all the complexities, often does not deliver practical solutions for the planet or humanity; we are advocates of Ockham’s razor. Considerations of the behaviour of farmers, car manufacturers, industrialists, and oil or gas producers are beyond the scope of our work. We concur that “to have net C storage or C stock increase in the soil, the sink has to be larger than the source”, which is basically the principle of the 4 per mille concept.
We wrote in our paper that the capacity of soils to sequester carbon is time constrained, which is stated clearly in the reports from France, New Zealand and Chile. Some countries reported that a new equilibrium will be reached (e.g., UK, Canada) and some others indicate that for some soils the maximum has already been attained (e.g., Scotland, New Zealand, Chile, USA, Belgium) and that the main challenge for these soil is not to lose the accumulated carbon. We referred several times to this finite potential in the discussion, at the beginning by stating on the finite capacity of the soil C sink. We were clear that soil carbon sequestration is reversible and stressed this in a large number of situations.
Baveye et al. then question the influence of spatial temperature gradients on carbon stocks in soils, and “the effect that temperatures rising globally over time as a result of climate change may have on these stocks”. Our Figures 2 and 13 clearly show the global effect of temperature on the world’s carbon stocks. We acknowledge that rising temperatures may have deleterious effects on soil carbon sinks, especially in extreme situations, mainly by accelerating mineralization in the cold climate regimes (permafrosts, northern hemisphere peats) and by reducing net primary production in hot-and-dry areas. However, in the intermediate situations, which are indeed those where increasing SOC is feasible, the effect of rising temperature is still under debate, which is complicated by the fact that not only temperature but precipitation and extreme events will change, and also by the fact that changes in land use may have a very large effect on C stocks. For instance, Fantappie et al. (2011) showed that climate change had a small influence on SOC variations in Italy. Minasny et al. (2012) found management practices have overridden the increase temperature in Indonesia and Korea, and similar results were found in China by Pan et al. (2010). Preliminary results from Stockmann et al. (2015) on worldwide changes in SOC over time suggest that land cover change is the primary agent that influences SOC changes over time, followed by temperature and precipitation. Arrouays et al. (2002) indeed acknowledged the effect of temperature on SOC dynamics but their report concluded that the overall effects of land use and soil management will be much more important for the forthcoming decades.
Baveye et al. cite the paper from Crowther et al. (2016) to support their argument about potential effects of temperature increase. The cited results are based on an extrapolation of a linear model fitted to 49 field experimental sites that modelled C decreases linearly as a function of temperature and time. Given the uncertainties on stock estimates and presumed decrease, these calculations are highly uncertain. Nevertheless, implementing C sequestration management will still be beneficial if climate warms up and has an effect on SOC. It will result in avoiding (additional) losses.
Unfortunately, the Crowther paper held dearly by Baveye was recently shot down. A critique letter showed the “a few extreme data points (high-leverage points) can strongly influence the slope of a regression line. Only 5 of the 49 sites analysed by Crowther et al. are in the upper half of the carbon stock range, which raises the possibility that the relationship they observed could be substantially altered by introducing data from sites with relatively high surface soil carbon stocks.”
We already discussed that the Crowther paper was a badly analysed paper, which managed to be published in Nature, was based on a regression of C decreases linearly as a function of temperature and time! Such simplistic equation was extrapolated to the world and following the style of Baveye, some seem to believe in such hype.
We recognize that some “management changes implemented to sequester more carbon in soils could lead to increased emissions of other, more potent greenhouse gases”. But we also know that some management changes could lead to decreased emissions of these gases. Therefore, we agree wholeheartedly that full management and a holistic perspective of GHG emissions is necessary. We also concur that SOC sequestration should be framed in the context of all ecosystem services linked to soils, but this was not the objective of our paper.
There are still many remaining questions about what is called the “priming effect” and its potential effects on subsoil layers. But we fear that the story of “priming effect”, as formulated by Baveye et al. may be interpreted as: “never add new carbon to soil, you’ll lose the old stuff and destroy the soil structure”. That would be an inaccurate and unfortunate interpretation.
Baveye et al. fear that policy-makers will, deliberately or not, misinterpret our statements. Saying that decision-makers may take this opportunity to “slow down dramatically the development and adoption of long-term solutions” is clearly making a case on assumptions about their intentions. This is another debate; we have chosen to write what we think is our best guess at the truth, not on how we think the policy-makers will interpret our best guess.
Theatrically perhaps, Baveye et al. further suggest that soil scientists adopt the Machiavellian view that the end justifies the means. We indeed believe that farmers in Australia, France and other parts of the world are more and more aware of the need to increase soil organic matter. Our discussion is not motivated by requests for additional funding but it is driven by the provision of a short- to medium-term solution to a global existential problem.
Baveye et al. then argue that the initiative will lead to politicians not sponsoring more fundamental research but will focus on more applied large-scale monitoring. They support their statement by the methodological debate that followed the publication of Bellamy et al. (2005). It is worth noting that this intense debate came about because Bellamy et al. found a large SOC decrease of 0.6% yr-1 in the topsoil of England and Wales from 1978 to 2003. We do not agree that large-scale soil monitoring is costly and complicated. When talking about large-scale soil survey and monitoring, we should keep in mind that most of the cost is in taking samples properly, after which, applications can be found on an amazing series of soil properties such as demonstrated in several countries for SOC, pH, phosphorus, K, trace elements, Si, PAH, pesticides, microbial DNA, etc. Baveye et al. prefer to jump to the “latest technology instruments”, which could be useful. But let the technology evolve a bit, and this will allow the instrument-driven users to work on samples from the monitoring programmes; this is already the case for a number of ‘-omics’ technologies such as successfully shown in France.
The goal of wide-extent soil monitoring is not as a funding scheme for a small group of scientists, but rather to provide an independent assessment of stocks and changes. In addition, the empirical data generated raise new scientific questions, which might not be apparent from hypothesis-driven experiments alone.
We have not promised the moon, but we do attempt a small commitment for the earth.
We do not think of this initiative in terms of subterfuge; we think plainly, and state openly, it 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.
Finally, quoting David Titley again:
Like any goal, the 2°C limit should be ambitious but achievable. However, if it is not met, we should do everything we can to meet a 2¼°C or 2.5°C goal.
Similarly 4 per mille is an ambitious target, and we shouldn’t be pessimistic and not even give it a try.
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