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.