.... When Dr. Keeling, as a young researcher, became the first person in the world to develop an accurate technique for measuring carbon dioxide in the air, the amount he discovered was 310 parts per million. That means every million pints of air, for example, contained 310 pints of carbon dioxide.

By 2005, the year he died, the number had risen to 380 parts per million. Sometime in the next few years it is expected to pass 400.  ....