Methane (CH4) is an important greenhouse gas because it has 25 times the global warming potential of carbon dioxide (CO2) bymass over a century1. Recent calculations suggest that atmospheric CH4 emissions have been responsible for approximately 20% of Earth's warming since pre-industrial times2. Understanding howCH4 emissions from ecosystems will respond to expected increases in global temperature is therefore fundamental to predicting whether the carbon cycle will mitigate or accelerate climate change. Methanogenesis is the terminal step in the remineralization of organicmatter and is carried out by strictly anaerobic Archaea3. Like most other forms of metabolism, methanogenesis is temperature-dependent 4,5. However, it is not yet known how this physiological response combines with other biotic processes (for example,methanotrophy6, substrate supply3,7, microbial community composition8) and abiotic processes (for example, water-table depth9,10) to determine the temperature dependence of ecosystem-level CH4 emissions. It is also not known whether CH4 emissions at the ecosystem level have a fundamentally different temperature dependence than other key fluxes in the carbon cycle, such as photosynthesis and respiration. Here we use meta-analyses to show that seasonal variations in CH4 emissions from a wide range of ecosystems exhibit an average temperature dependence similar to that of CH4 production derived from pure cultures of methanogens and anaerobic microbial communities. This average temperature dependence (0.96 electron volts (eV)), which corresponds to a 57-fold increase between 0 and 306C, is considerably higher than previously observed for respiration (approximately 0.65 eV)11 and photosynthesis (approximately 0.3 eV)12. As a result, we show that both the emission ofCH4 and the ratio of CH4 to CO2 emissions increase markedly with seasonal increases in temperature. Our findings suggest that global warming may have a large impact on the relative contributions ofCO2 andCH4 to total greenhouse gas emissions from aquatic ecosystems, terrestrial wetlands and rice paddies.