MAUNA LOA OBSERVATORY, Hawaii - The readings at this 2-mile-high station show an upward curve as the world counts down to climate talks: Global warming gases have built up to record levels in the atmosphere, from emissions that match scientists' worst-case scenarios.

Carbon dioxide concentrations this fall are hovering at around 385 parts per million, on their way to a near-certain record high above 390 in the first half of next year, at the annual peak.

"For the past million years we've never seen 390. You have to wonder what that's going to do," said physicist John Barnes, the observatory director.

One leading atmospheric scientist, Stephen Schneider, sees "coin-flip odds for serious outcomes for our planet."

Far from this mid-Pacific government observatory, negotiators from 192 nations gather in Copenhagen, Denmark, next month to try to agree on steps to head off the worst of the climate disruptions researchers say will result if concentrations hit around 450 parts per million - in 30 years at the current rate. Some say the world has already passed a danger point, at 350 ppm, and must roll back.