Sequestering carbon dioxide is essential if the world is going to avoid the worst impacts of climate change. Many scientists estimate that in order to stay at a “safe” level of warming, that carbon dioxide levels should stabilize around 350 parts per million. Last year we reached 410 ppm. In short, there is already too much carbon dioxide in the atmosphere, and we need to sequester carbon dioxide now. Sequestration can be accomplished naturally, by growing trees for example, or through technology.
Trees and other plants are a wonderful carbon sink. In the process of photosynthesis, plants remove carbon dioxide, the most prevalent manmade greenhouse gasses and a major contributor to climate change, and store or sequester the carbon in leaves, branches, roots and the soil.
Different ecosystems sequester carbon differently. Carbon is stored above ground in the living vegetation and below ground in the soil. The above-ground and below-ground storage pools are both important, but in most terrestrial ecosystems, more carbon is stored in the soil. Wetlands, arctic ecosystems, conifer forests, and grasslands are generally the most effective at storing carbon. These ecosystems store large quantities of carbon in the soil, where it is resistant to decay due to lack of oxygen (wetlands), cold temperatures (arctic and some coniferous ecosystems), acidic conditions (wetlands and conifer forests), or the fact that much of the carbon has been converted to soot (grasslands).
The age of a forest matters too. Young forests with trees between 4” and 16” in diameter will take more carbon dioxide out of the air on an annual basis, while mature stands with trees having a diameter greater than 18” have a larger pool of stored carbon. Although the amount of carbon pulled out of the air annually slows down as forests age, research shows that mature and old-growth forests continue to sequester carbon indefinitely, and the large amount of carbon already stored makes older forests critically important for keeping that carbon locked away.
As important as trees are to sequestering carbon dioxide, some of the carbon dioxide is released back into the atmosphere as leaves, branches and trunks rot, when trees are burned, or when harvested wood products are discarded. For example, the recent Australian forest fires are expected to push carbon dioxide levels to their highest concentration since the beginning of the industrial era. This new carbon dioxide put into the atmosphere will be captured by growing trees and other vegetation. In turn this vegetation will rot or burn and the carbon dioxide released back into the environment. This is what is known as the carbon cycle.
Technology can also be used to sequester carbon dioxide. Carbon capture and sequestration and carbon capture and utilization capture carbon dioxide in the flue gasses at power plants and then sequester it or utilize the carbon. By far the most frequent use of this captured carbon dioxide is for enhanced oil recovery. (How climate friendly is that?) There may be other uses for captured carbon dioxide, including building material, carbon fiber, polymers, and fuel.
Carbon capture and sequestration is expensive and consumes enormous amounts of power. Appalachian Power Company tried it at their Mountaineer plant in New Haven, West Virginia. Although the process could remove 90% of the carbon dioxide, it almost doubled the cost of electricity and took up acres of land. Eventually, APCo abandoned the project.
Some see carbon capture and sequestration as a waste of time and money and the last gasp of the coal industry. Yet the United Nation’s Intergovernmental Panel on Climate Change has said that developing this technology is essential if the earth is going to avoid the worst impacts of climate change. This technology will also be needed to reduce carbon dioxide from hard to decarbonize industries: namely steel and cement. And if the United States could make this technology feasible, we could export the technology to China and India who have shown little interest in moving beyond coal-fired utilities.
There is another technology to remove carbon dioxide, called direct air removal. Rather than trying to capture carbon dioxide in the flue gasses, direct air capture removes carbon dioxide from the ambient air. It too is currently too expensive to operate, and there is uncertainty that carbon dioxide can be safely stored underground for hundreds, or even thousands, of years. Yet, it may become a vital technology in addressing climate change.
Planting trees — even President Trump supports planting a trillion trees over the next decade — is an important strategy. Beyond trees, we will need negative emission technology if the earth is going to avoid the worst impacts of climate change.
NOTE: The Highlands Conservancy is participating in several tree plantings activities. To learn about how to participate, see the information on p. 11.
Editor’s Note: This is the first of a series (possibly monthly) columns on climate change from the Conservancy’s Climate Change Committee. The committee is comprised of Perry Bryant (Chair), Jackie Burns, Kent Karriker, Hugh Rogers, Marilyn Shoenfeld, Larry Thomas, Jeff Witten, and Frank Young.