Comparing the climate change mitigation potentials of alternative land uses:Crops for biofuels or biochar vs.natural regrowth

Using biomass from dedicated crops for energy production and natural vegetation regrowth are key elements in future climate change mitigation scenarios.However,there are still uncertainties about the mitigation potentials that can be achieved by the different land-based systems and how they perform relative to each other.In this study,we use harmonized future land use datasets to identify global land areas dedicated to second generation bioenergy crop production in 2050 under different climate scenarios.We then assess the global climate change mitigation potentials of using biomass for producing bioethanol with(BECCS)or without carbon capture and storage,biochar,or a synthetic fuel(e-methanol).For the latter,the electricity required to produce hydrogen for e-methanol synthesis is sourced from either wind power or the projected average electricity mix in 2050.Mitigation potential from natural regrowth on the identified land is also quantified.For all the cases,we modelled emissions of greenhouse gases from the life-cycle stages and use parameterized models to estimate local biomass growth rates.The identified land areas range from 1.95 to 13.8 million hectares and can provide from 30 to 178 mega ton(Mt)dry biomass annually from dedicated crops.Climate change mitigation potentials range from 11 to 257 MtCO_(2)-eq.yr^(−1),depending on technological option and land availability.The largest mitigation is delivered by BECCS,but e-methanol can achieve similar findings when hydrogen is sourced from wind power.If hydrogen is produced from grid electricity,e-methanol can result in net positive emissions.E-methanol can also deliver more final energy than bioethanol(4.04 vs.1.27 EJ yr^(−1)).Natural vegetation regrowth can generally achieve higher mitigation than bioethanol,but less than biochar.An optimal combination of BECCS and natural vegetation regrowth can achieve a larger mitigation,up to 281 MtCO_(2)-eq.yr^(−1),indicating that integrated solutions can help to achieve successful land management strategies for climate change mitigation.

Biomass residue to carbon dioxide removal:quantifying the global impact of biochar

The Climate Change Conference of Parties(COP)21 in December 2015 established Nationally Determined Contributions toward reduction of greenhouse gas emissions.In the years since COP21,it has become increasingly evident that carbon dioxide removal(CDR)technologies must be deployed immediately to stabilize concentration of atmospheric greenhouse gases and avoid major climate change impacts.Biochar is a carbon-rich material formed by high-temperature conversion of biomass under reduced oxygen conditions,and its production is one of few established CDR methods that can be deployed at a scale large enough to counteract effects of climate change within the next decade.Here we provide a generalized framework for quantifying the potential contribution biochar can make toward achieving national carbon emissions reduction goals,assuming use of only sustainably supplied biomass,i.e.,residues from existing agricultural,livestock,forestry and wastewater treatment operations.Our results illustrate the significant role biochar can play in world-wide CDR strategies,with carbon dioxide removal potential of 6.23±0.24%of total GHG emissions in the 155 countries covered based on 2020 data over a 100-year timeframe,and more than 10%of national emissions in 28 countries.Concentrated regions of high biochar carbon dioxide removal potential relative to national emissions were identified in South America,northwestern Africa and eastern Europe.

SEQUESTERING ORGANIC CARBON IN SOILS THROUGH LAND USE CHANGE AND AGRICULTURAL PRACTICES:A REVIEW

Climate change vigorously threats human livelihoods,places and biodiversity.To lock atmospheric CO_(2)up through biological,chemical and physical processes is one of the pathways to mitigate climate change.Agricultural soils have a significant carbon sink capacity.Soil carbon sequestration(SCS)can be accelerated through appropriate changes in land use and agricultural practices.There have been various meta-analyses performed by combining data sets to interpret the influences of some methods on SCS rates or stocks.The objectives of this study were:(1)to update SCS capacity with different landbased techniques based on the latest publications,and(2)to discuss complexity to assess the impacts of the techniques on soil carbon accumulation.This review shows that afforestation and reforestation are slow processes but have great potential for improving SCS.Among agricultural practices,adding organic matter is an efficient way to sequester carbon in soils.Any practice that helps plant increase C fixation can increase soil carbon stock by increasing residues,dead root material and root exudates.Among the improved livestock grazing management practices,reseeding grasses seems to have the highest SCS rate.