A new report from the FAO, the Food and Agriculture Organisation of the United Nations, shows that well-managed grasslands are critical in the struggle to reduce carbon emissions.
Grasslands cover around 20 per cent of the Earth’s surface and hold roughly a fifth of terrestrial carbon stocks.
The FAO’s Global Assessment of Soil Carbon in Grasslands has found that annual grassland sequestration could be increased by 17 per cent in the top 30cm of soil alone. This finding is important to the delivery of the 4 per 1000 initiative, launched by the French government in Paris at COP 21.
The 4 per 1000 initiative says that if the level of carbon stored by soils in the top 30 to 40 centimetres of soil increased by just 0.4 per cent (or 4 per cent) per year, “this would nearly compensate for the annual CO2 increase of the atmosphere.” The FAO’s report shows that nearly a fifth of this target could be delivered in grasslands alone.
The FAO’s Global Assessment says, “Soils can act as both sources and sinks of carbon and many grasslands have suffered losses of soil organic carbon (SOC) because of anthropogenic activities such as intensive livestock grazing, agricultural uses and other land-use activities. This trend, however, could be reversed by stimulating plant growth, capturing carbon in the soil, and protecting carbon in highly organic soils.”
In its analysis, the FAO aimed to estimate the baseline SOC stocks of grasslands in the year 2010, assess the carbon input levels needed to maintain current SOC stocks and determine if such carbon input is available under current conditions.
They found that globally, grassland soils stored an estimated 63.5 Mt of carbon in the year 2010 at 30 cm soil depth, with unimproved (semi-natural) systems storing slightly higher amounts than improved (managed) systems (33.8 vs 29.8 Mt C). On average, in the year 2010, the SOC under unimproved grasslands was 53 tonnes C/ha and 50 tonnes C/ha in improved grasslands. The findings of this analysis show that there is room for additional carbon storage in grassland soils.
The FAO estimates suggest that 17 per cent of the 4 per 1000 target could be reached in the top 30 cm of grasslands and continue over at least 20 years after adoption of SOC enhancing management, such as the incorporation of animal manures, agroforestry and rotational grazing.
The FAO recommends that grassland systems particularly prioritise carbon returns in deteriorated soils that have a negative carbon balance and protect SOC in unimproved grasslands with high carbon stocks.
The analysis focussed only on grasslands and did not analyse SOC in intensive croplands or forestry where most carbon losses occur.
The report concludes that, “sequestering carbon via increases in the soil component on grasslands is an achievable and potentially effective route to quickly increasing carbon sequestration in the near term.”