A net-negative emissions technique that combines bioenergy with carbon capture and storage (BECCS) would indeed threaten global food security and require unsustainable quantities of water and fertiliser, researchers have found.
The BECCS concept involves the planting of fast-growing trees and grasses that draw down carbon dioxide (CO2) from the atmosphere as they grow. The plants would then be used as bioenergy fuel for a range of processes, including electricity production. But instead of their combustion releasing the CO2 back into the air, it would be captured and stored deep underground indefinitely, thus resulting in a net reduction of atmospheric greenhouse gases.
In recent years however, a number of analysts have expressed concern about the vast amount of land and other resources that would be required for such an endeavour, although there are other net-negative options that do not involve such a large resource footprint.
This week, a paper in Earth’s Future, a journal of the American Geophysical Union, produced by researchers with the Potsdam Institute for Climate Impact Research was among the first to attach some hard numbers to these worries about BECCS.
Their aim was to calculate precisely how many resources in terms of land, water and other inputs would be needed for BECCS under three different climate action scenarios. The first is essentially business as usual, with no significant emissions mitigation efforts performed. The second foresees modest levels of climate mitigation action being taken by the world’s governments, thereby likely leading to an average global temperature increase of 2.6°C above industrial times by 2100, and BECCS would thus be needed to make up for all of this lack of action. And the third envisages much more ambitious action by governments likely leading to a temperature increase of 1.7°C by century’s end, with BECCS needed to play a smaller role in repairing the emissions ‘overshoot’.
The first scenario would require such an amount of land as to eliminate virtually all natural ecosystems.
The second would require more than 1.1 gigahectares (equivalent to over a billion rugby pitches) of the most productive agricultural land or elimination of more than half the world’s natural forests. This would “severely compromise food production and/or biosphere functioning,” the researchers conclude.
Even the third scenario would require high inputs of water and fertilizers in order to avoid “fierce competition” for land.
As a result, the researchers conclude that BECCS is not an alternative to aggressive GHG mitigation efforts, but could play the role of a “valuable supporting actor” alongside such efforts so long as BECCS schemes are put in place immediately and so long as they are sustainably maintained.
The study considered the issue from a global perspective, concluding it is not an effective tool at that level. But there are regions of the world where beneficial biomass plantations can be sited. A 2015 paper appearing in Nature Climate Change found that a carbon-negative power system in western North America by 2050 could indeed by achieved via BECCS, and that such a system could also be used to reduce transport and industrial emissions.
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