George W. Bush was grilled on air pollution in Texas and a number of other serious issues last night by none other than Dave Letterman. Letterman, who had Bush as a guest on his late night show, told the governor he thought it was a joke when he heard that Bush is pushing for oil drilling in ANWR. Later, Letterman talked up the need for alternative energy sources, then said, “Sooner or later we’re going to have to make a significant change.” Bush said, “I think we can do that.” To which Letterman responded, “Not just lip service, not just an item on a campaign. The polar ice cap is melting, that’s all I know.” Meanwhile, Democratic vice presidential candidate Joe Lieberman warned yesterday that Bush would roll back 30 years of environmental progress. And on Wednesday, he talked up the religious basis for his and Al Gore’s environmental commitment. Lieberman: “If you believe in God, I think it’s hard not to be an environmentalist.”