Physicist Stephen Hawking says pollution coupled with human greed and stupidity are still the biggest threats to humankind. During an interview on Larry King Now, the science superstar told King that in the six years since he’s spoken with the talk show host people haven't cleaned up their act. “We certainly have not become less greedy or less stupid,” Hawking said. “The population has grown by half a billion since our last meeting, with no end in sight. At this rate, it will be eleven billion by 2100.” He noted that the massive problem of pollution has only grown in the last five years. “Air pollution has increased over the past five years,” he said. “More than 80% of inhabitants of urban areas are exposed to unsafe levels of air pollution.” When asked what the biggest problem facing the world is, Hawking said climate change. Hawking told King he wonders if we are past the point of no return.  "Will we be too late to avoid dangerous levels of global warming?" There are some things even Hawking doesn't know.