According to a recent study¹, Earth has narrowly missed entering into a new glacial. And the reason why? CO2 levels were too high.
But the CO2 that ‘saved’ us from a rather more icy existence is not the product of the mass burning of fossil fuels you are probably thinking of now. The CO2 we are talking about here was already in the atmosphere before the industrial revolution began (~1850).
Pre-industrial revolution greenhouse gas levels are generally used as a baseline from which to measure human contributions to atmospheric concentrations. Pre-industrial CO2 levels were ~280 parts per million (p.p.m.), we are now at over 400 p.p.m. However, humans have been influencing Earth for a long time before this.
Despite being on a different scale from today’s emissions, over the thousands of years that deforestation and agriculture have been occurring, these activities will have affected CO2 levels. Some studies even suggest that without human activity, pre-industrial CO2 could have been as low as 240 p.p.m.³.
Modelling studies now show that if pre-industrial CO2 concentrations had indeed been at 240 p.p.m., present day Earth would be a much colder place, with large ice sheets already existing and a full glacial to look forward to¹.
So although by no means proven fact, it is possible that early human activity may have prevented Earth from entering an ice age.
However, at the end of this story, global warming is still the bad guy.
If a 40 p.p.m. increase in CO2 over thousands of years can essentially counteract an ice age, what is the additional 120+ p.p.m. we’ve pumped into our atmosphere capable of doing?
¹ Ganapolski, A., Winkelmann, R. & Schellnhuber, H. J. (2016). Critical insolation-CO2 relation for diagnosing past and future glacial inception. Nature, 529, 200-203.
² wikipedia.org/wiki/Ice_Age (Yes, I know, but it had the prettiest picture)
³ Ruddiman, W. F. (2013). The Anthropocene. Annual Review of Earth and Planetary Sciences, 41, 45-68.
For a professional summary of this research see: Crucifix, M. (2016). Earth’s narrow escape from a big freeze. Nature, 529, 162-163.