A carbon cycling model developed for the renewable Energy Danish Island, Samsø

• A carbon cycling model (CCM) is needed to assess the total CO2 emission from an area.
• The CCM can be used to set up a carbon balance for the considered area.
• The CCM can be used as a powerful environmental management tool.
• The CCM can inform about the emission consequences of various project proposals.

Renewable energy has replaced the major part of the energy use on the island Samsø during the first decade of the 21st century and it leads to the key question: How much less carbon dioxide and methane are presently emitted from the island Samsø as a result of the introduction of renewable energies? Furthermore, we would like to know, what we can do to reduce the carbon dioxide emission further and where it is most sensible to take action in order to do this.When renewable energy is introduced to replace the use of fossil fuels, a significant reduction of the carbon dioxide emission is to be expected, but it is not necessarily the case. To assess the carbon dioxide emission it is necessary to obtain knowledge about all the processes which involve carbon. Emission of a significant amount of carbon dioxide is the result of a number of natural processes for instance decomposition processes of organic matter in nature, and nature is also by the photosynthesis taking up carbon dioxide from the atmosphere. Therefore, in order to find the resulting net emission of carbon dioxide and answer the above mentioned questions, the development of a carbon cycling model (CCM) for the area or region is needed. A total of 26 different carbon pools are considered in the CCM of Samsø, including the various agricultural products, three fractions of carbon in soil, forests, wetlands, grasslands, straw used for heating and the production in the industry (Trolleborg). The transfer processes among the various pools are quite well known from literature and estimates of the agricultural and industrial production on the island can be derived from available data. It is furthermore known how much forest, wetland and grassland, that Samsø has and how many inhabitants that live on the island, how much solid waste they produce and how much carbon dioxide they respire. The CCM has been developed based on this knowledge and has furthermore been adapted to follow the annual variations.Due to the use of renewable energy, it can be shown by the CCM that Samsø to day net removes 26 460 t carbon per year in form of carbon dioxide (97 020 t/year of carbon dioxide is removed), while no carbon dioxide was net removed in 1997, before introduction of renewable energy on the island. The model is applied as environmental management tool. If it is assumed that Samsø is fossil fuel free and 5000 t carbon is removed by the use of supplementary crops, as much as almost 40 000 t of carbon as carbon dioxide will be removed from the atmosphere. This amount corresponds also to more than the difference between carbon exported and imported, which means that Samsø is even removing in this case the carbon that is emitted as carbon dioxide in the towns when the agricultural production from Samsø is utilized as food.A clear improvement of the carbon dioxide is therefore possible by the use of these two measures: make Samsø a fossil fuel island and use supplementary crops. These applications of the CCM show that the model can be used as a powerful management tool. It is the intention to use the CCM in the coming years to find the solutions for the development of the energy use on Samsø that will yield the biggest reduction of the emission of carbon dioxide and other green house gases.