redOrbit: Researchers have reconstructed atmospheric carbon dioxide levels over the past 2.1 million years in the sharpest detail yet, shedding new light on its role in the earth’s cycles of cooling and warming. The study, in the June 19 issue of the journal Science, is the latest to rule out a drop in CO2 as the cause for earth’s ice ages growing longer and more intense some 850,000 years ago. But it also confirms many researchers’ suspicion that higher carbon dioxide levels coincided with …