Current understanding of the global cycling of carbon dioxide, methane, and nitrous oxide.

To address the climate change caused by anthropogenic emissions of greenhouse gases into the atmosphere, it is essential to understand and quantitatively elucidate their cycling on the Earth's surface. This paper first presents an overview of the global cycling of three greenhouse gases, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), followed by a description of their variations in the atmosphere. This paper then presents the recent global budgets of these greenhouse gases estimated using two different approaches, top-down and bottom-up. Discussions on our current knowledge regarding the global cycling of the three gases are also presented.