In the Nordic Strategy for Sustainable Development an objective is “to work to stem climate change and help prepare our regions and the rest of the world for the changes that will be needed” (Nordic Council of Ministers 2009). To do that, it is essential to understand the carbon balance as this defines how emissions of greenhouse gases, especially carbon dioxide and methane, from anthropogenic activities translate into concentrations of greenhouse gases in the atmosphere and control important climate feedback mechanisms (Houghton et al. 2007). Estimating and mapping carbon sinks and sources are therefore major issues concerning also the agreements of the United Nations Framework Convention on Climate Change (UNFCCC) in the Kyoto protocol. It is needed to ensure maximum cost effectiveness of actions taken to mitigate anthropogenic emissions of greenhouse gases. However, surface exchange of greenhouse gases are highly affected by anthropogenic forcing (changes in land use and management) and climate forcing. Therefore, to understand and predict these impacts using models, it is important to quantify realistically how much carbon is taken up by the terrestrial and marine ecosystems. Thus, detailed knowledge of the exchange of the greenhouse gases between land, ocean and atmosphere is important, and the processes involved must be fully understood and accurately quantified. However, large uncertainties on the estimations of carbon exchange remain.