Anthropogenic Influences on the Global Carbon Cycle and its Implications for the Future Abstract Carbon makes up approximately 50% of the dry weight of all living things; it forms the structure of all life on Earth. While not one of the major atmospheric gasses, carbon compounds such as carbon dioxide (CO 2 ) and methane (CH 4 ) are major greenhouse gases, and as such are major contributors to global warming. Currently atmospheric CO 2 concentrations are increasing at a rate of about 3.2 Pg C per year. Based on ice core data and ongoing atmospheric CO 2 monitoring, anthropogenic sources, specifically combustion of fossil fuels and land use changes, have been cited for causing this increase. Here we give a brief overview of how the natural carbon cycle works and look at how fossil fuel combustion and land use changes affect this cycle over time. We focus on the modifications that have been, and could be made to land use, as well as the potential for carbon sequestration as a mitigation for atmospheric carbon build up. Natural Carbon Cycle OCEAN UPTAKE ­ Dissolving of CO 2 gas into the oceans and inflow of carbon carried from land by rivers. OCEAN RELEASE ­ Return of carbon in the oceans directly back to the atmosphere as CO 2 gas. SEDIMENTATION ­ Slow burial of plant and animal matter on land and on the ocean floor, which eventually becomes limestone, coal, gas, and oil. RESPIRATION ­ Slow combustion of carbon compounds, producing energy within organisms and releasing CO 2. PHOTOSYNTHESIS ­ Conversion of CO 2 into energy-rich carbon compounds by plants. The Earth maintains a natural carbon balance. Carbon is continually exchanged within a closed system consisting of the atmosphere, oceans, biosphere, and landmasses. When, natural perturbations in concentrations of carbon dioxide (CO 2 ) occur, the system gradually returns to its natural state through the processes shown here. These process can be either long term or short term. Human Impacts On The Carbon Cycle Fossil fuel combustion and land use changes, are the main ways in which humans affect the natural carbon cycle. The natural carbon system cannot keep pace with these new anthropogenic emission sources. The natural processes that permanently remove this additional carbon (i.e. ocean uptake and sedimentation) work extremely slowly so, the concentration of CO 2 in the atmosphere increases. Effect of CO 2 & Greenhouse gases Pushkaraj Sardesai and Sarah Eggleston Earth System Science and Policy Biomes CO 2 emissions from combustion of fossil fuels is of concern because combustion adds the long dormant stock of C from Earth’s crust in to the active carbon cycle. This increased CO 2 concentration in atmosphere is a major factor in global warming. The potential ways to reduce the CO 2 concentration in atmosphere are 1) Carbon sequestration 2) Replace fossil fuels with bio-fuels 3) Reduce the CO 2 release from energy use (by switching to alternative sources of energy) References rst.gsfc.nasa.gov/ Sect16/Sect16_4.html images/figure4.gif 1) Janzen, H.H. “Carbon cycling in earth systems – a soil science perspective.” Agriculture, Ecosystems & Environment 104 (2004) ) Jorge L. Sarmiento & Steven C. Wofsy Co-Chairs A U.S Carbon Cycle Science Plan. A report of the Carbon and Climate working Group ) 4) Fossil Fuel CO 2 emission and carbon sequestration With help of atmospheric modeling and satellite images, determine the effective radius from a point source within which the concentration of CO 2 are high. With help of satellite images identify the type and concentration of biomass in the area. Determine the uptake of carbon dioxide by this biomass. (carbon sequestered). Determine the potential for carbon sequestration with help of local man managed ecosystems. e.g. Trees planted in this radius will sequester carbon more effectively and rapidly then elsewhere, and reduce overall national emissions. Fig8_small.jpe Possible way to mitigate Point Source Carbon dioxide Pollution Humans change the way land is used in many ways. The most significant of these ways is through deforestation, desertification, conversion of land to cropland, and wetland destruction. The map above shows the basic location and extent of major Earth biomes. What biomes are changed is of significant importance to the carbon cycle, as each biome has a different potential for carbon storage. Grasslands Boreal Forest Tundra Desert Chaparral Temperate Forest Alpine Tropical Forest Savanna Carbon Storage Potential of Biomes As can be seen in the graphs to the left, carbon storage capacity varies by biome. Currently the Boreal Forest biome stores the most carbon, followed by Tropical Forests. In terms of total carbon per unit area, Wetlands are by far the most efficient at carbon storage with Boreal Forests next in efficiency. For carbon sequestration purposes, the amount of carbon that can be stored by a biome is quite important. The location of these biomes is also important, since the majority of carbon is emitted in the Northern Hemisphere. The location of biomes such as the Boreal Forest with their ability to store large amounts of carbon can make a great difference for atmospheric carbon concentrations.