This paper in the journal Biogeosciences is a comprehensive overview of issues relating to methane releases from hydrates (also called “clathrates”) in response to climate change. The paper describes natural sources of methane, the radiative forcing of atmospheric methane, and the geology and transport of methane hydrates. It discusses mechanisms by which undersea methane is released, including deep-ocean warming, pockmarks in the sea floor, and undersea landslides. It describes the fate of undersea methane released by such methods. It also discusses land-based methane deposits in permafrost (as peat or hydrates). Table 1 estimates sizes of methane reservoirs and likely release quantities and timeframes. Past releases are discussed, including the Storegga landslide, the Paleocene-Eocene thermal maximum, and the clathrate gun hypothesis as it relates to interglacial warming. The paper concludes by assessing risks posed by methane release: a sudden release doomsday scenario (unlikely), chronic release over centuries similar in magnitude to anthropotenic methane release rates (likely), and releases over many thousands of years similar in quantity to all fossil fuel emissions (worst case).
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