NEW YORK (TheStreet) -- Natural gas prices to date have increased nearly 3% and are expected to double over the next few years as U.S. producers gain access to international markets and excess supplies begin to shrink.A chief energy economist said a turnaround in natural gas prices is imminent, following the International Energy Association's (IEA) bullish outlook and warm weather forecasts. The IEA forecasts that by 2015, natural gas prices will increase to an average $9 a million Btu in Europe, $5.60 a million Btu in U.S. and $11.50 a million Btu in Japan. As per the IEA report, natural gas demand worldwide could rise more than 50% by 2035, amounting to more than a quarter of global energy demand as compared to the current 21%. The report further added that ample supplies of cheap natural gas, strong demand from emerging markets and the cloud over nuclear energy could be the forerunners for a "Golden Age" for natural gas. The U.S., accounting for almost 19.2% of global supply, is the world's biggest natural gas producer, recent IEA statistics show. For the first time ever, the Department of Energy authorized and approved a plan for Houston-based Cheniere Energy ( LNG to export liquefied natural gas from a terminal in Louisiana. Although exports may push U.S. natural gas prices higher, they would still be trading three times lower than in the European and Asian markets.