We got into the fossil-fuel business and started releasing massive amounts of CO2 into the air. Some of it was picked up by the ocean, some by the land. However, about half of it remained in the air. And we went from an atmospheric concentration of around 283 parts per million (ppm) in 1807 to 391 ppm as of 2011. This CO2 concentration is the highest in the last 800,000 years and potentially for the past few million years.
Photo By Fotolia/Vitaly Krivosheev