evidence: The most basic reason is that fossil fuels—the result of millions of years of plant growth—are the only source of carbon dioxide large enough to raise atmospheric carbon dioxide amounts as high and as quickly as they have risen. The increase between the year 1800 and today is 70% larger than the increase that occurred when Earth climbed out of the last ice age between 17,500 and 11,500 years ago, and it occurred 100-200 times faster. In addition, fossil fuels are the only source of carbon consistent with the chemical fingerprint of the carbon present in today’s atmosphere. That analysis indicates it must be coming from terrestrial plant matter, and it must be very, very old. These and other lines of evidence leave no doubt that fossil fuels are the primary source of the carbon dioxide building up in Earth’s atmosphere. During all of the cycles between ice ages and warm periods over the past million years, atmospheric carbon dioxide never climbed higher than 300 parts per million. At the end of the last ice age around 20,000 years ago, it was 280 ppm. Today it is close to 420 ppm. The increase between the year 1800 and today is 70% larger than the increase that occurred when Earth climbed out of the last ice age between 17,500 and 11,500 years ago, and it occurred 100-200 times faster. Only fossil fuels—which are the remains of millions of years of carbon uptake by plants—contain enough carbon to produce such a massive change in such a short time.