Inland Water Greenhouse Gas Budgets for RECCAP2: 1. State‐Of‐The‐Art of Global Scale Assessments

Inland waters are important emitters of the greenhouse gasses (GHGs) carbon dioxide (CO2 ),methane (CH4), and nitrous oxide (N2O) to the atmosphere. In the framework of the 2nd phase of the REgionalCarbon Cycle Assessment and Processes (RECCAP-2) initiative, we review the state of the art in estimatinginland water GHG budgets at global scale, which has substantially advanced since the first phase of RECCAPnearly 10 years ago. The development of increasingly sophisticated upscaling techniques, including statisticalprediction and process-based models, allows for spatially explicit estimates that are needed for regionalizedassessments of continental GHG budgets such as those established for RECCAP. A few recent estimatesalso resolve the seasonal and/or interannual variability in inland water GHG emissions. Nonetheless, theglobal-scale assessment of inland water emissions remains challenging because of limited spatial and temporalcoverage of observations and persisting uncertainties in the abundance and distribution of inland water surfaceareas. To decrease these uncertainties, more empirical work on the contributions of hot-spots and hot-momentsto overall inland water GHG emissions is particularly needed.