A six-year experiment in burying carbon dioxide under the ocean has been highly successful, according to the scientists behind the project. Since 1996, CO2 emitted during methane gas exploration in the North Sea has been pumped back into the ground, where it has been trapped in a giant bubble almost a third of a mile under the floor of the ocean. The CO2 would otherwise have been released into the atmosphere, contributing to climate change. The storage technique, known as carbon sequestration, has been proposed as a way to allow humans to continue to burn fossil fuels without contributing to global warming. In the North Sea, the Norwegian company Statoil has so far used sequestration to store 5 million tons of CO2 underground. Andrew Chadwick of the British Geological Survey said of the technique, “We believe it is safe; it is certainly technically feasible and really has very little environmental downside.”