We may adjust the period, but I do not think people are suggesting that we're making an irreversible change to the planet? Planet heats up, various complex mechanisms kick in, planet cools. The million-year average temperature of this planet is mostly governed by distance to the closest star. Is there much discussion about our planet getting closer to the sun? I don't pay much attention. If it was, I would very much listen to Dr. Dyson. Our fear and panic is about an irreversible change to the planet as we know it -- those complex mechanisms may not be pleasant for current life on the planet (ask the Dinosaurs, or anything living through an Ice Age). Environmentalism is mostly about conservation and continuity of the present biosphere. The planet will be fine, the planet will continue to have a climate, the climate will continue to cycle.