Matt Ridley is my favorite optimist. In a recent essay in Wired, he has a bit of fun with the doom and gloomers, primarily because they are so often wrong. A few quotes:
"Ever since Thomas Robert Malthus, doomsayers have tended to underestimate the power of innovation. In reality, driven by price increases, people simply developed new technologies, such as the horizontal drilling technique that has helped us extract more oil from shale."
"Humanity is a fast-moving target. We will combat our ecological threats in the future by innovating to meet them as they arise, not through the mass fear stoked by worst-case scenarios."