Q.1051: What is the role of Forest in Carbon Cycle?
The subject of global warming elicits vivid conversations from scientists, politicians, students, and private citizens alike. Reports of mountain glaciers disappearing, rising ocean water levels, forests and farmlands being lost, and ozone holes have provoked concern among many people about the state of the global environment.
Carbon dioxide (CO2) is the most abundant human-influenced greenhouse gas. A greenhouse gas is found naturally in the atmosphere— in the upper atmosphere it captures sunlight energy and reflects it back to earth, in turn creating heat. This "blanket" of gas moderates the earth's temperature. With increasing levels of carbon dioxide, however, research suggests that a thicker blanket will produce global warming.
Carbon dioxide is an important molecule for life. All plants that photosynthesize absorb CO2 from the air, combine it with water, nutrients, and the energy from the sun to produce food and oxygen. The carbon in CO2 is the building block of plant life— in a pound of wood, for example, there is approximately 1/2-pound of carbon! The oxygen in CO2 is necessary for all animals. Animals breath it, in turn converting it back to carbon dioxide. This carbon cycle (see the image below) is an essential link among all life as we know it.
Aside from over 6 billion human beings breathing out CO2 every day, certain human activities produce large quantities of it. CO2 is released during energy production and automobile use; carbon dioxide is released into the atmosphere during the combustion of carbon-containing fossil fuels such as coal, oil, petroleum, and natural gas.
When the carbon cycle is in equilibrium, the amount of carbon released from storage (e.g. from the burning of fossil fuels or the decay of plant matter, for example) is being stored (e.g. in tree wood). The idea is that we are now producing more carbon dioxide than our current plant landscape can capture. So, with all this "extra" CO2, is there anything we can do to help slow global warming?
One idea for capturing additional carbon is to take advantage of forested areas as carbon sinks. All the plants in a forest absorb CO2, but trees are especially good at long-term storage. In trees, CO2 is converted to carbon stored in wood. Wood holds carbon as long as there is no rotting, and even when wood rots, it releases carbon very slowly. If the wood from a tree is turned into a forest product, then the carbon becomes stored in that product! A chair, a 2-by-4, and a wooden salad bowl all hold carbon until they rot.
The more forests we have, then, the more carbon we can capture. The more carbon we capture, the fewer greenhouse gases we contribute to the atmosphere. While planting trees cannot offset all the greenhouse gas production related to human activities, it certainly does help! Along with every human being producing less CO2 (using less gas and coal, for example), forests really might make a difference.
What is carbon sequestration?
Carbon sequestration is absorption and capture of carbon from the atmosphere. Trees capture carbon out of the atmosphere as long as they are growing, and they store the carbon throughout their life, even after harvest. Burning wood products as fuel releases the same carbon back into the atmosphere that was once captured by the trees, resulting in a net zero carbon impact. Recycling results in no CO2 releases, since the fiber continues to be used. Composting results in net zero emissions, since CO2 emitted by aerobic decomposition was originally sequestered. Landfills, on the other hand, result in anaerobic decomposition, which produces methane and carbon monoxide in addition to CO2, and can multiply that carbon impact by as much as 20 times.