EcoWatch: A significant threshold has been crossed by renewable energy as analysts report that the sector's size last year reached double the level it was at just 10 years earlier. This expansion happened in a year when the global economy and energy use both grew, but without a matching rise in emissions of carbon dioxidethe main greenhouse gas targeted in efforts to restrain global warming. The report by REN21, a global renewable energy policy network, says the result is an example of sustainable development....