HOLLYWOOD - Leonardo DiCaprio joined environmentalists to give Americans a pre-Halloween scare on Oprah Winfrey's talk show yesterday, when he warned about the dangers of global warming. The Titanic star presented a segment from a politically charged new documentary, called Global Warming, which he narrates, and explained he felt the last year's hurricanes and tsunamis are just a terrifying warning of what is to come.DiCaprio and Dr. Michael Oppenheimer, a professor at Princeton University, attempted to explain the "complicated issue" of global warming, emphasizing that America, which boasts five percent of the world's population, produces 25 percent of the globe's carbon emissions.The actor stated, "Global warming is not only the number one environmental issue that we're facing today, but one of the most important issues facing all of humanity."We're in a situation right now where we're basically emitting too much of this carbon pollution from our cars and our electric power plants that burn coal into the atmosphere, and it's causing our planet to heat up."Winfrey listened intently as DiCaprio warned about the dangers of ignoring the problem, and then said, "You feel like Noah (biblical character who built an arc in preparation for a great flood) to me—you’re like, 'Pay attention, pay attention, pay attention.'"Winfrey then confessed she owns one of the five worst sports utility vehicles on a new emissions list, prompting DiCaprio to state, "That's OK, as long as you change that."