Thursday in Pittsburgh, Republican presidential candidate and former Massachusetts Gov. Mitt Romney appeared to shift his position on climate change. Speaking at the Consol Energy Center, he said, "My view is that we don't know what's causing climate change on this planet." In his book No Apology and in earlier public appearances, Romney has said that he believes climate change is occurring — and that humans are a contributing factor. At a campaign appearance in New Hampshire back in August, Romney emphasized questions about the extent of the human role. But his remarks in Pittsburgh represent a clear shirt toward a skeptical position on the causes of climate change.