Sections of the pipelines lie at a depth of around 80-110 metres. The escaped natural gas is almost entirely methane, which partially dissolves in water and is not toxic. The deeper the gas is released in the sea, the higher the proportion that dissolves in the water. Methane is the second biggest contributor to climate change after carbon dioxide. David Hastings, a retired chemical oceanographer in Gainesville, Fla., says much of the gas would rise through the ocean and enter the atmosphere. "There is no question that the largest environmental impact of this is to the climate, because methane is a really potent greenhouse gas," he said.