Reuters: U.S. President Barack Obama came to Denmark to promote Chicago’s Olympic bid, but will he come back to push for a treaty to save the world from climate change? That’s the question environmentalists asked on Friday as he made a five-hour stop in Copenhagen where he was rebuffed in his bid to get the International Olympic Committee to pick his adopted hometown of Chicago to host the 2016 summer Games. The activist group Greenpeace said it had hung a banner with the words “Right …