By 2009 global carbon dioxide (CO2) concentrations have already reached 387 parts per million (ppm), up by 40 percent from 275 ppm in 1900. Until recently a doubling to 550 ppm was widely regarded as an acceptable target, but this has been revised downward to some 450 ppm as new scientific evidence about a warming planet has emerged. Now a growing number of climatologist are questioning even this limited increase, and argue for an actual reduction of CO2 concentrations to 350 ppm or below. This goes way beyond scenarios currently being proposed by goverments in developed countries, whose policies are homing in on 80 percent reduction of carbon emission from 1990 figures by 2050.
The problem is that every year we are now discharging nearly 10 billion tonnes of carbon into the atmosphere. Of this, four to five billion tonnes are not being reabsorbsed into the world's ecosystems, but are instead accumulating in the atmosphere above our heads. According to the Global Carbon Project, the land and ocean carbon sinks-such as forests, and plankton in the ocean-removed about 54 percent, or 4.8 billion tonnes a year, of the carbon that human discharged into the atmosphere between 2000 and 2007. That leaves a carbon surplus of about 4 billion tonnes or so per year, which we need to find ways to reduce or absorb. For global temperatures to stabilize, carbon emisssions must ultimately not exceed what can be absorbed by the biosphere, the Earth's vegetation, soils and oceans. So can we enhance the capacity of bioshere to absorb CO2?
The earth's natural sinks of CO2 are ocean, forests and, perhaps most importantly, soil. The global soil carbon pool is estimated to amount to 2,500 Gt, whereas the biotic (vegetation based) pool is 560 Gt. A key point to be considered is that whilst fossil-fuel burning massively increased in the last 300 years, the capacity of biosphere to absorb it has been significantly reduced at the same time. Dr. Rattan Lal, Professor of Soil Science at Ohio State University, has calculated that 476 billions of tonnes (Gt) of carbon has been emitted from farmland soils due to inapproriate farming and grazing practice, compared with 270 Gt emitted from over 150 years of burning fossil fuels.
Most agricultural soils have lost anything of their antecedent soil organic carbon pool, or a total of 30 to 40 tC/ha. Carbon loss from soils is mainly associated with soil degradation and has amounted to 78+/-12 Gt since 1850. Thus, the present organic carbon pool in agricultural soils is much lower than their potential capacity.Considering all greenhouse gases, the global technical mitigation potential from agriculture is between 1.5 and 1.64 gigatonnes of carbon equivalent per year by 2030.
In addition to measures for enriching farmland and pastures with 'conventional' organic matter, a very significant new option is becoming available under the heading of 'biochar'.
This application related to the FAO states that soil carbon sequestration can take effect very quickly and is a cost-effective win-win approach which combines mitigation, adaptation, increased resilience and the promise of more reliable and increased crops yield. The biochar particles can improve soil structure, and enhance the presesnce of micro-organisms and plant nutrient. Adding biochar to the soil not only enhances fertility and life in the soil, but also helps it to retain moisture-which is very important in an age of climate change.
The FAO is also working on tools to measure, monitor and verify soil carbon pools and fluxes of greenhouse gas emission from agricultural soils, including cropland, degraded land and pastures. With global population expected to grow to nine billion by 2050, and with increasingly uncertain oil and water supplies,well-thought-out new approaches to securing carbon-rich organic soil can help to secure the food supplies of future generations. Professor Johannes Lehman of Cornell University and others have calculated biochar applications to soil could remove several billion tonnes of carbon from the atmosphere per year.