I'm looking at a chart (produced by NOAA, August 14, 2008) showing the fluctuation of Earth's temperature over just the last 400,000 years. That is a period of just 1/10,000 of our planet's existence, but twice as long as we homo sapiens have been around. In that time frame there have been 4 ice ages and 4 brief inter glacial periods wherein global temperature is in the sweet spot for human development. Those lovely warm periods tend to last for but a few thousand years and happily we are in one right now. In terms of earth's geological history however, it will end in the blink of an eye. There is absolutely nothing we humans can do about that except prepare ourselves for the next ice age.