One thing that has been absolutely proven is that the Earth exists, and that it has abundant life on it. It has continued to do so despite changes in the atmosphere, solar input, and drastic bombardments from space.
During very ancient times, CO2 concentrations in the atmosphere were up to 20 times what they are now. Life thrived, and we didn't turn into Venus. Doesn't mean it isn't something to watch--warming will change climate in some areas, and affect things like crops and other issues. Some places are going to get worse, and some are going to get better. Humanity has been through changes before, too, even in our recorded history.
History of Atmospheric CO2 through geological time (past 550 million years: from Berner, Science, 1997). The parameter RCO2 is defined as the ratio of the mass of CO2 in the atmosphere at some time in the past to that at present (with a pre-industrial value of 300 parts per million). The heavier line joining small squares represents the best estimate of past atmospheric CO2 levels based on geochemical modeling and updated to have the effect of land plants on weathering introduced 380 to 350 million years ago. The shaded area encloses the approximate range of error of the modeling based on sensitivity analysis. Vertical bars represent independent estimates of CO2 level based on the study of ancient soils.
