Mitigation of black carbon – and sulphur dioxide – emissions proceed with current technologies and improve health and environmental outcomes. Mitigation of carbon dioxide from fossil fuel use will need a range of technologies in a number of sectors – not merely electricity generation. It is likely to proceed by fits and starts over decades as technologies emerge. Mitigation of carbon dioxide from agriculture and forestry is not merely possible but the reversal of global soil degradation can reverse historic soil carbon loss and sequester 78 billion tonnes of carbon. At achievable rates of sequestration in soils some 25% of current greenhouse gas emissions for 40 years. Restoring soil carbon in agricultural soils lifts productivity. Agricultural productivity builds local markets and global wealth. Wealth provides resources for solving problems. Conserving and restoring ecosystems, reversing biodiversity loss, safe water and sanitation, better health and education outcomes, updating the diesel fleet, better ways of cooking, etc.
Estimates of particulate black carbon (BC) climate forcing are very uncertain. The level of scientific understanding (LOSU) is at best classed as medium. The direct effects of BC are some 1.1W/m2 – with broad uncertainties indicated by the error bars in the graph below. Net climate forcing from all other factors is some 1.5W/m2. Warming from carbon dioxide from fossil fuels is 1.6W/m2. The black carbon estimation problem is further confounded by co-emission of particulate organic aerosols (POA) and sulphur dioxide (SO2).
The problem has a further complication in the mixing ratio of BC to co-emitted species. “Modelling studies have estimated that (1) the net radiative effect of black carbon (BC) and organics generated by fossil-fuel combustion and biomass-fuel cooking contribute to a warming, (2) open burning leads to net cooling4,5 and (3) the net warming effect of fossil-fuel BC is larger than that of biomass-fuel cooking6,7. Furthermore, BC warming is regulated by the ambient concentration of sulphates resulting from sulphur dioxide (SO2) emissions2. Sulphate strongly reflects solar radiation, whereas BC strongly absorbs solar radiation. Thus the net radiative forcing is determined by the relative amounts of BC and sulphate. However, BC is invariably internally mixed with sulphates8 and solar absorption by BC is amplified when it is internally mixed with sulphates1,9,10.” Ramana et al 2010
It suggests two things. First, that the large warming potential of BC is best addressed through controls on fossil fuel emissions – technologies that are already implemented broadly in the west. Secondly, that most of these emissions are now generated in the developing world. The colours on the map correspond to emissions in the graphic immediately below.
Emissions by region are shown below.
The burning of forests, grasslands, fields and biomass in cooking fires has other implications. Again this is mostly happening in the developing world. Global emissions of greenhouse gases from land use change and agriculture are some 26% of total anthropogenic emissions. We can compare this to electricity – 28%, transportation – 12.2%, residential use of fossil fuels – 8.5% and manufacturing and construction – 11.8%.
Wind, solar and nuclear power do little to address biodiversity, development, soil and water conservation, particulate emissions or any of the multitude of other human and environmental problems. Even at 100% substitution – it is just 28% of greenhouse gas emissions. Addressing emissions from energy supply as a whole requires a range of innovative technologies across sectors. It is evident that short term gains even on emissions are elusive – let alone the diversity of other issues. Refocusing on restoring living soils on agricultural lands – both grazing and cropping – provides short term gains on multiple objectives.