claim: at the end of recent ice ages, the concentration of carbon dioxide in the atmosphere started to rise only after temperatures began to climb.
evidence: Concentrations of CO 2 in the atmosphere were as high as 4,000 parts per million ( ppm, on a molar basis ) during the Cambrian period about 500 million years ago to as low as 180 ppm during the Quaternary glaciation of the last two million years.