Fossils and CO2

Someone recently pointed out to me that CO2 levels are the highest they have been for 100 million years. I remarked that it was because we are burning 100 million year old fuel.

My statement was somewhat true. While CO2 levels were probably a little higher 130 thousand years ago, fairly close to the dawn of mankind, it was quite a long time ago. The fuels we use today, so-called fossil fuels including oil, gas, and coal, were formed over millions of years from decomposed organic matter. The orders of magnitude are different, but the gist is the same.