Why soil carbon sequestration is overrated
Increasing the carbon content of agricultural soils is promoted by several international policy initiatives (like the UN, the EU & the IPPC) as a win-win action for both climate change mitigation and food security. Researchers of Wageningen University & Research (WUR) and a colleague from PBL Netherlands Environmental Assessment Agency show that such a win-win is the exception, not the rule, as a benefit for the one often leads to a loss for the other. Recently, they published their findings in a perspective paper in Global Change Biology.
Reviewing more than 21 meta-analyses, observed yield effects of increasing soil carbon are inconsistent, ranging from negative to neutral to positive.
Renske Hijbeek (WUR): ‘Soils are extremely complex and variable, and caring for them to ensure maintained food production under climate change will require implementation of a range of practices that are adapted to each local context instead of focusing on a one-size-fits-all solution.’
Overrated contribution to climate change
Using an extensive literature review and modelling, the researchers found little justification for the current global excitement around soil carbon sequestration. While estimated contributions of soil carbon sequestration to climate change vary, almost none take account the fact that the increment in soil carbon always wears off over time to reach a maximum – the saturation level.
If soil carbon saturation is included in calculations, the contribution of soil carbon sequestration to climate change mitigation is reduced by 53-81% compared to current estimates.
No justification of current global agendas
The researchers conclude in their paper that the existing knowledge base does not justify the current global agendas that focus first and foremost on soil carbon sequestration. ‘Moving away from climate-smart soils, a shift is needed towards soil-smart agriculture, adaptative and adapted to each local context, where multiple soil functions are quantified concurrently,’ Gabriel Moinet (WUR) states.
‘Only such comprehensive assessments will allow synergies for land sustainability to be maximised and agronomic requirements for food security to be fulfilled. Soil carbon sequestration may occur along this pathway and contribute to climate change mitigation, and should be regarded as a co-benefit.’