If we go by co2, the guess is that something between 1,000 - 1,500 ppm is required to tip us into a greenhouse phase. Our current levels are well under 500 ppm

If we go by co2, the guess is that something between 1,000 - 1,500 ppm is required to tip us into a greenhouse phase. Our current levels are well under 500 ppm. Humanity will have to work very hard to force the planet out of its current icehouse. We are definitely having an impact, and could well drive ourselves extinct, but I still see us as unable to implement drastic change, especially as some extinction events have required thousands of years to come to pass.