Philadelphia Inquirier: Michael Mann switched from physics to climate science back in graduate school because he thought climate offered a better chance to work “on a frontier.” He got his wish, and now, as the director of Pennsylvania State University’s Earth System Science Center, he has experienced an aspect of frontier life more like the Wild West – a bounty on his head. After dozens of Mann’s personal e-mails were hacked in November, the tenured professor has been called a fraud, a clown, and …