MANCHESTER, N.H. — In the first town hall of his freshly announced presidential campaign, Mitt Romney yesterday reaffirmed his view that global warming is occurring and that humans are contributing to it, a position that has been rejected in recent years by many Republicans as the issue has taken on a greater partisan tinge. After opening remarks in which Romney blamed President Obama’s policies for the new anemic hiring figures, the first questioner from the floor — a software developer from Hanover, N.H. — wanted to know the candidate’s position on climate change, an issue his opponents have generally avoided...