Group members preparing summary: Mia Visser, Jennifer Peyser, Connie Bernard, and Henna ChouReading Summary:
Carbon is both naturally produced and sequestered in terrestrial systems. Swamps and marshes have by far the highest density of soil carbon, while nearly half of Earth's plant carbon is stored in tropical seasonal and tropical evergreen forests. Boreal forests also make up a considerable amount of plant carbon, while temperate forests, grasslands, and pasture make up a less significant storage. However, cultivated land in temperate zones has less than half the capacity as native prairies, due to its catalyzing of microbial activity, which converts soil carbon to carbon dioxide. Besides tillage, other human activities that have reduced stored carbon include the addition of nitrogen fertilizers to the soil, the draining of wetland areas such as prairie potholes, and deforestation. Reducing plant and soil carbon has decreased stored carbon by one-third to one-half, but changing agricultural and forestry management practices in areas such as the Midwestern U.S. could again reduce atmospheric carbon. Another process that contributes CO2 to the atmosphere is the burning of fossil fuels, which is the probable main reason for the changing ratios of carbon's three isotopes, C12, C13, and C14. The C12 isotope is the most abundant and is the only carbon isotope created by combusting fossil fuels, while the latter two are created by radiation in the biosphere. Given enough time, C13 and C14 will decay back into C12, but the large ratio of C12 to the other two isotopes indicates the great effect that fossil fuel use has on the transfer of stored carbon to atmospheric carbon. Anthropogenic contributions of CO2 such as fossil fuel emissions from automobiles and power plants will likely only continue to increase due to world population growth and increasing industrial activities of developing countries. Even if all human-caused emissions ceased, it would take fifty years to reduce the atmospheric CO2 concentration to the 1980 level. Methane, the most increasing gas, is also the second greenhouse gas after CO2. It comes from wetlands, enteric fermentation (one quarter of the human emissions), oceans, coal mining and natural and gas industry, with a human contribution as large as natural sources. Its actual concentration is 1.7 PPM, versus 360 PPM for CO2, and is increasing at 1% per year versus 0.6% for CO2. So methane is at less concentration but increase at a larger rate than CO2. However, its capacity of IR absorption is 20 times as effective as CO2. A solution against this effect would be to burn CH4: 2 CH4 + 4 O2 -----> 2 CO2 + 4 H2O. All the methane will produce carbon dioxide, reducing the global warming potential, but increasing its stage in the atmosphere. It could be a solution to approve because methane could increase more and more with the animal production as it is the tendency in China and South and East Asian countries. Another gas, carbon monoxide has the shorter lifetime after CO2 and CH4. Its comes most from anthropogenic sources as fossil fuel combustion than natural sources.
Online Discussion Summary:
Several interesting questions were posed in the online discussion area for 1-5. One post pointed out that there is a large store of methane hydride buried in the ocean. It was wondered if removing this to use as fuel would be an economically and environmentally viable alternative to the use of fossil fuels. No response was given. Someone also posted regarding the last paragraph of the online summary. It was regarding the fact that CO is more reactive CO2. He stated that the incomplete combustion of fossil fuels would result in more CO being produced than CO2. He wondered if we could use incomplete combustion to produce more CO, which might then be reacted with another molecule to turn it into something relatively harmless. It was noted that this might not be a good idea due to the less heat obtained per mole with incomplete combustion as well as the fact that CO is toxic to humans. No follow up was posted. Another person wondered if someone could clear up the concept of the Missing Carbon Sink, both talked about in lecture and in the online summary. The follow up included a summary of the mathematical breakdown of the data used. This included the following statement: "Atmospheric increase (3.3) = fossil fuel emissions (5.5) + net changes in land use (1.6)- Oceanic uptake (2)-missing carbon sink (1.8)." She also mentioned that direct evidence of uptake is only documented in the countries of northern-mid latitudes. So with the data that we currently have the most reasonable estimate for where the Missing Carbon Sink lies is in central United States. A website address was also included. Another post brought up a question inquiring about the non-balancing of the carbon between the soil and vegetation in a particular area. The follow up response was well put together and informative. It summarized that there isn't a balance because of factors effecting vegetative growth as well as factors effecting the build-up and release of CO2 in the soil. The fact that some areas are better suited for the microbial breakdown that is necessary to release stored CO2 in the plants, while other soils are less able to support these types of organisms due to factors such as lack of oxygen. For example the tropical rain forests, with its abundant supply of these beneficial microbial organisms is deficient in soil carbon due to the rapid break down of vegetation. While soil in areassuch as swamps and marshes have relatively high soil carbon content compared to the vegetation due to lack of oxygen available to support carbon-fixing organisms. She also talked about the idea of paying farmers to store carbon in the soil through different land management practices.
Lecture summary:
In Lecture much of the summary reading material was reiterated. Something that was pointed out was that we know that much of the carbon in the atmosphere is due to anthropogenic causes because of the decrease in ratio of C14 relative to C12. This shows us that much of the Carbon released is due to the burning of fossil fuels. We also compared carbon concentrations in vegetation and soil for different environments. In a tropical evergreen forest most of the carbon is in the vegetation and not the soil. In a temperate grassland or pasture most of the carbon is in the soil as opposed to the vegetation. One important aspect to remember when looking at carbon cycle is that time scales change. At present each person is putting in 21 tons of carbon per year. What we put into the atmosphere takes about 60 years to reduce to half of what we initially put in.