The possibility of methane-hydrate decomposition due to global climate changes is investigated using the world ocean model. It is supposed that the temperature of the ocean surface rises up to 1.5º during 50 years and then decreases to 1.5º. The climatic model of the ocean is integrated for the period of 2500 years and simulates penetrations of warming from the surface deep into the ocean. A three-dimensional equation of transport of dissolved methane from sources is simultaneously solved. The methane flux into the atmosphere has reached from 4.4 to 7.3 Tg/year, depending on a warming scenario.