Global methane emission from wetlands and its sensitivity to climate change

Abstract The concentration of atmospheric methane (CH4) exerts a strong influence on atmospheric chemistry and the global climate. Natural and cultivated wetlands (rice paddies) are important sources of CH4, and the extent and strength of these sources may increase as a result of global warming and extension of rice production. Emission of methane from wetlands is an ecosystem process, closely coupled to local climatic and soil environments which influence complex processes of plant growth, soil organic matter decomposition, methanogenesis and CH4 oxidation. Rates of emission show large variation in both space and time and their estimation from point measurements or from correlation with net primary production is difficult and unreliable. Here we report a study in which process-based ecosystem models were used to estimate global CH4 emissions from natural wetlands and rice paddies, and the sensitivity of the models to simple climate change scenarios were tested. Our estimate of global emission was 145 Tg yr-1, of which 92 Tg yr-1 came from natural wetlands and 53 Tg yr-1 from rice paddies. The emissions from wetlands at high-latitude and rice paddies were only half of those reported in the traditional literature, confirming more recent measurements. The models also showed that modest global warming may produce a higher CH4 emission, but that this effect may be reversed by larger increases in temperature, due to the effect of soil moisture depletion.

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