Global investment in renewable energy was a record $148 billion in 2007, jumping 60 percent from 2006, the United Nations reported Tuesday. About one-third of the investment went to wind power; solar power was the fastest-growing clean-energy sector from 2006 to 2007, with investment nearly doubling to hit $28.6 billion. Investment in biofuels dropped in the same time period, falling to $2.1 billion. Most clean-energy investing is happening in Europe, says the report, followed by the U.S.; China, India, and Brazil are also seeing significant investment, while “sub-Saharan Africa, arguably the region that has the most to gain from renewable energy, remains largely unexploited.” The report expresses optimism that an international climate-change treaty will emerge in 2009 and that the next U.S. president will “make renewable energy and energy efficiency a political priority” — two factors that would help ensure that clean-energy investment continues to rise.