Large amounts of the greenhouse gas methane are stored beneath the ocean floor in a stable form called hydrate. Hydrates occur naturally under high pressure and low temperatures. Water molecules freeze and encage methane with ice thus stabilizing it into solid form. The Arctic contains large reservoirs of these hydrates, and they can melt in increasing tempo due to global warming. This could cause more methane to be released from the ocean floor. Methane is much stronger greenhouse gas than CO2.