(Reuters) - Presidential hopeful Mitt Romney broke with Republican orthodoxy on Friday by saying he believes that humans are responsible, at least to some extent, for climate change. "I believe the world is getting warmer, and I believe that humans have contributed to that," he told a crowd of about 200 at a town hall meeting in Manchester, New Hampshire. "It's important for us to reduce our emissions of pollutants and greenhouse gases that may be significant contributors."