Spring is in the air, but what is it? The blossoms blossoming? The vernal equinox? Yes to both, and one more: It's how a young American chemist named Charles David Keeling stumbled upon proof of a climate problem way back in 1959. Here's how he made his astonishing discovery—and why the Bloomberg Carbon Clock just started running backwards. By 1956, he had brought his experiment to Scripps Institution of Oceanography at UC San Diego, where he would work until his death in 2005. The possibility that industrial CO2 emissions were warming the world was a viable but untested idea at the time. Keeling faced a phenomenal opportunity: to set up a monitoring station 11,135 feet up the side of a mountain, in the middle of the ocean, where his machine could sniff the clear air. "He got brought down to Scripps to run this enormous program at a very young age," Ralph Keeling, Dave Keeling's son and a prominent Scripps geochemist, said in an interview late last year.