London Oil giant Royal Dutch Shell said it was sued for causing climate change, but that, like some other global warming cases taken against energy companies by environmentalists, the cases were dismissed. The Anglo-Dutch group said in its annual report, published Thursday, that, \"together with other energy companies\" it was subject to climate change litigation taken by parties it did not name \"We believe these lawsuits are without merit and are not material to Shell,\" the world\'s second-largest non-government controlled oil company by market value added. Scientists believe carbon dioxide emissions from burning fossil fuels such as oil and gas are a major cause of global warming. A spokesman said the cases related to Hurricanes Katrina and Rita and had been dismissed years ago. He said the comment in the report reflected Shell\'s view that any future lawsuits of a similar nature would also be without merit. Successful battles Companies have generally been successful in such legal battles. Last year, the US Supreme Court rejected a lawsuit against five big power companies that sought to force them to cut their carbon dioxide emissions, claiming the utilities had created a public nuisance by contributing to climate change. The oil industry has worked hard for over a decade to position itself as part of the solution to global warming rather than its principal culprit. Natural gas, which accounted for around half of Shell\'s 2011 output, produces around half the CO2 that coal does, to yield a similar amount of energy. Companies have sought to expand markets, and prices, for gas, by telling governments the quickest way to cut CO2 emissions was to replace coal-fired power plants with gas turbines, and for gas to be adopted as a transport fuel. The advocacy effort has accelerated in recent years after an explosion of shale gas production in the United States led to a collapse in natural gas prices.