The soil carbon opportunity
Cutting fossil fuel emissions is not enough to avoid dangerous climate change. Too much carbon is already in the atmosphere, and the oceans are continuing to heat. The Intergovernmental Panel on Climate Change stated in 2007 that "Complete elimination of CO2 emissions is estimated to lead to a slow decrease in atmospheric CO2 of about 40 ppm over the 21st century" (about 9% to 1985 levels; see IPCC's 7 Mb pdf file here, section 10.3).
In other words, the strategy of reducing carbon dioxide emissions, by itself, has little effect or leverage on the atmospheric concentrations. By treating global heating as a problem of energy, emissions, or technology alone, we only get to decide whether to wreck our climate slightly faster or slightly slower.
There is a biological side to global warming and the carbon cycle. Carbon is a main ingredient of all life, and of its remains. While planting trees is rightly discounted as a way to reduce atmospheric carbon, we could increase soil organic matter (58% carbon by dry weight) rapidly and cheaply. This will pull excess carbon out of the atmosphere while also enhancing soil fertility, water quality, food quality and human health, and also reducing floods, droughts, and agriculture's dependence on fossil fuels and chemicals.
How it works
Biological processes, such as photosynthesis and respiration, drive 99% of the carbon cycle. There is more carbon in soils than in vegetation and the atmosphere combined. Soil carbon can be more stable than plant carbon (less subject to oxidation or burning).
Good topsoil is rich in organic matter. To create topsoil, combine minerals, air, water, living things in the soil, living things on the soil, and intermittent disturbance such as grazing (we typically overlook these last two). Do not turn the soil over with plows. Because the roots of perennial grasses give off carbohydrates, and periodically die off, carbon-rich topsoil can be formed fastest by grasslands. The cast-off grassroots, and the carbohydrates exuded by these roots, nourish entire underground communities of soil organisms. These interactions over time produce stable organic matter from dead plant material.
Outside inputs are not always required, but management is---working with rather than against biospheric processes such as water and nutrient cycling.
Why this may be surprising news
- Soil organic matter is underground and mostly invisible. The processes that form it are not always well understood, and are not part of most people's ecological awareness.
- Large economic sectors benefit from our dependence on purchased agricultural inputs rather than on the processes of soil formation, and government policies abet this dependence. The creation of topsoil and organic matter, as well as its connection to the climate problem, was developed by various strands of alternative agriculture, which are outside the major institutions and centers of power.
- Most of the measurements and assessments of the soil carbon opportunity by scientists and academics have been done where biosphere or ecosystem processes are dysfunctional, as in many industrial farming systems. The gains in soil carbon reported from these situations are mediocre, suggesting soil carbon as a mitigation strategy only.
- Common beliefs such as the following have helped to hide the soil carbon opportunity:
- microbes don't count, except pests and diseases
- soil is mainly a geological product, and soil biology or cover is not important
- water or nutrient availability is a matter of inputs, not biology
- global warming is basically a pollution problem, and technology is to blame
- new knowledge is easily and quickly spread, even across disciplinary boundaries, and accredited experts know best.
- New instruments, such as remote sensing satellites, and new research are continuing to reveal the huge role of living organisms in biospheric processes. (See Spencer Weart's fascinating account of the discovery of biology by climate science.) Our beliefs tend to lag behind.
- The biological formation of soil organic matter is not a technical solution. We prefer technical solutions, and have trouble recognizing the value of biological processes.
- The soil carbon opportunity does not fit into the polarized emotion spectrum of the climate debate, in which climate change skeptics and those who want to control carbon emissions attack and ridicule each other.
The development of soil organic matter in cropland and grassland soils in the world could take atmospheric carbon concentrations down to preindustrial levels, if we also quit burning fossil fuels. (See the calculation.) This would require a transformation of agriculture and land management, and of decision making and politics as well---all tending to increase the resilience of local communities.
Much current federal and local policies work against the creation and retention of soil organic matter. The farm bill, federal public lands policies, and state and local policies all have a huge bearing on soil organic matter, as does the structure and function of a carbon market. The newly formed Soil Carbon Coalition would like your help in spreading awareness of the opportunity and in developing sound policies.