16.6: What Have We Learned So Far?

Natural and working lands can both contribute to climate change and help to mitigate it. What is needed to bend the curve? “Carbon-friendly” land management is key to reducing emissions and increasing carbon capture, conversion, and storage. Field-tested solutions are needed. These must consider the full life cycle of carbon and greenhouse gases to be truly effective. A systems perspective is critical. Ecosystems are complex, and thus cross- and multidisciplinary collaborations may be necessary to devise and implement comprehensive climate change solutions for natural and working lands. In addition to research, training and outreach are important components of successful strategies. Educating yourselves and others on the concepts of the carbon cycle and our ability to alter it through everyday decisions is perhaps the most effective strategy to solving the climate change crisis. Making decisions about how to fertilize fields and supporting climate-friendly practices with our purchasing power are examples of actions that we can take today,

Summary

• Greenhouse gas emissions reduction is critical for slowing climate change, but emissions reduction alone is no longer sufficient to solve the problem. We must remove carbon dioxide from the atmosphere to bend the curve.
• Ecosystems are complex and management approaches must embrace that complexity to be successful. Trade-offs, for example between carbon sequestration and enhanced greenhouse gas emissions, need to be identified, quantified, and carefully weighed for effective climate change mitigation outcomes.
• Plants need CO2 from the atmosphere to survive and grow. They convert CO2 to plant tissues via photosynthesis. The annual pattern in the drawdown of CO2 by plants is evident at a global scale in the concentrations of atmospheric CO2.
• Microorganisms in the soil break down plant litter into soil organic matter. Microbes also respire CO2, returning some of the carbon originally captured by plants to the atmosphere, completing the carbon cycle. The annual pattern in respiration of soil microorganisms is detectable at a global scale in the concentrations of atmospheric CO2.
• Plants and soils are reservoirs of carbon. Soils are the largest reservoir of carbon on the land surface. Plants are a smaller reservoir of carbon but are key conduits for moving carbon from the atmosphere to the soil.
• Soils are the basis for life on Earth. They are a complex mixture of minerals and organic matter. They house and feed microorganisms and support plants. They are a source and a sink of greenhouse gases.
• All ecosystems produce some greenhouse gases, as this is an indicator of life. Land management can increase greenhouse gas emissions. Agriculture accounts for approximately 25% of global greenhouse gas emissions.
• Soil organic matter contains carbon that was originally captured by plants. Soil organic carbon pools vary across locations because they are affected by climate, by plant, animal, and microbial species, and by underlying geology.
• Soils can accumulate organic carbon when the rate of inputs exceeds the rate of losses. This is called soil carbon sequestration.
• Photosynthesis can be thought of as a “technology” that has been perfected and deployed for over 2 billion years. The rate of atmospheric carbon uptake by plants via photosynthesis dwarfs all other forms of carbon capture.
• Plants can accumulate and store carbon. Trees and forests store more carbon than other plant life. Forest carbon is vulnerable to fire and logging, as well as pest outbreaks. Tropical deforestation accounts for 10% of annual greenhouse gas emissions globally.
• Emissions reduction from working lands is critical for climate change mitigation. There are several possible ways to lower emissions. Many of these approaches have valuable co-benefits for land owners and managers. Fertilizer and livestock waste management are examples of promising avenues for emissions reduction.
• Soil carbon sequestration holds great potential as a carbon sink. Large areas of the land surface have become depleted in soil organic carbon through management over the last 12,000 years. Many land use practices have already been shown to increase soil carbon storage.
• Soil carbon sinks can be divided into three categories: those that slow emissions and allow carbon to accumulate, those that increase the rate of carbon capture by plants, and those that use amendments to stimulate plant growth, increase carbon storage, and reduce emissions in other sectors.