Yes, you read that correctly , three million - million - years ago CO2 levels on Earth were the same as they are today, but there is one major difference between three million years ago and today. Three million years ago, we humans were not driving cars or eating the meat that requires cow farts; we weren't barbecuing or refusing to recycle or building factories; there was no Industrial Age, no plastic, no air conditioning, no electricity, no lumber mills, no consumerism, no aerosols. In fact, three million years ago, there were probably no human beings on Earth, at least not human in the way we use that term today.