OSLO, Norway — Levels of carbon dioxide, the main greenhouse gas emitted by burning fossil fuels, hit a record high in the atmosphere in 2006, accelerating global warming, the World Meteorological Organization (WMO) said on Friday. But concentrations of methane, the number two heat-trapping gas, flattened out in a hint that Siberian permafrost is staying frozen despite some scientists’ fears that rising temperatures might trigger a runaway thaw. ‘In 2006, globally averaged concentrations of carbon dioxide in the atmosphere reached their highest levels ever recorded,’ the WMO said. Carbon dioxide is the main gas from human activities blamed by the U.N. climate panel for stoking warming. The WMO said levels rose 0.53 percent from 2005 to 381.2 parts per million of the atmosphere, 36 percent above levels before the Industrial Revolution began in the 18th century. Levels of nitrous oxide, the number three greenhouse gas produced by burning fuels and by industrial processes, also rose to a record with a 0.25 percent gain in 2006. Levels are 320 parts per billion, 19 percent above pre-industrial times. ‘Atmospheric growth rates in 2006 of these gases are consistent with recent years,’ the WMO said in a report. […]