United Press International: A new Gallup Poll shows a high level of awareness among Americans about global warming, but a far lesser degree of worry about the phenomenon. The survey released Monday reported that while 80 percent of Americans said they understood the issue, only 40 percent believed it would become a serious threat in their lifetimes. About a decade ago, a poll showed that 25 percent feared climate change would be a serious problem in their lifetimes. Two-thirds of Americans say they …