Bloomberg: Irreversible effects of global climate change such as arctic ice melt and lost water supplies may still be averted if the world stops using coal-fired power plants, a leading NASA scientist said. James Hansen, director of NASA’s Goddard Institute for Space Studies, said the planet is at a “tipping point” that could lead to rising sea levels, severe droughts and floods, and reduced fresh water supplies if world leaders don’t act to reduce emissions such as carbon dioxide. He …