The estimate of the methane emission from hydrates is based on the data indicating to the location and potential thickness of the hydrate stability zone. Gas hydrate abundance in the marine sediment depends on the gas concentration and the available pore space within certain stability limits. In this paper, we establish the methane ocean environment, based on the latitudinal distribution of the methane hydrate stability zone, for a range of geothermal gradients and sediment porosities. The possibility of the methane hydrate decomposition due to the global climate changes is investigated using the world ocean model. It is supposed that the temperature of the ocean surface rises up to 1.5 degree during 50 years and then decreases to 1.5 degree. The climatic model, supplemented with a one-dimensional model of a bottom sedimentary layer of the ocean, is integrated for a period of 2000 years and simulates penetrations of warming from the surface deep into the ocean and sediments. A three-dimensional equation of transport of dissolved methane from sources is simultaneously solved. The methane flux into the atmosphere has reached 2 Tg/year.