Siberian wetlands: Where a sink is a source

A greenhouse gas inventory can for some ecosystems be based solely on the net CO 2 exchange with the atmosphere and the export of dissolved organic carbon. In contrast, the global warming effect may be more complex in ecosystems where other greenhouse gases such as CH 4 or N 2 O have significant exchanges with the atmosphere. Through micrometeorological landscape‐scale measurements from the largest wetlands on Earth in West Siberia we show that CH 4 has a stronger effect than CO 2 on the greenhouse gas budget in terms of radiative forcing on the atmosphere. Direct measurements of the CO 2 and CH 4 exchange during the summer of 1999 show that these wetland ecosystems, on average, acted as net sinks of carbon of 0.5 g C m −2 day −1 but large net sources of CH 4 . Given the high Global Warming Potential of CH 4 , the Siberian wetlands are an important source of radiative forcing, even in comparison to anthropogenic emissions.