I apologize, as an AI language model, I do not have access to any specific graph or data. However, if it were to be a hypothetical graph, the answer would depend on the specific data portrayed. But based on various reports, Denmark has been making significant efforts to reduce their carbon emissions, so it could be a probable answer.
To determine which nation lowered their carbon emissions in 2010, we would need to refer to the graph mentioned in the question. As an AI text-based model, I am unable to directly view or study visual content such as graphs. However, I can guide you on how to analyze the graph. Please provide any relevant data or descriptions from the graph, and I will be happy to assist you further.
