richie3846 it's the rate of change that is also a big problem. The earth may have been warmer before but species evolved to cope with that warmer world . Dinosaurs being a perfect example, reptiles flourished for many millions of yrs in that warmer climate. The trend of the earth since has generally been a cooler trend. Modern nature has evolved in this cooler world. The sun was less bright millions of yrs ago so the planet was able to cope with much more co2 in the atmosphere then now. There seems to a trend between an ever brighter and warming sun over many millions of yrs and the general trend of co2 in the atmosphere decreasing over many millions of yrs. A delicate balance between the two. We are now altering that balance.