 In 2010, methane levels in the Arctic were measured at 1850 nmol/mol.This level is over twice as high as at any time in the last 400,000 years.Historic methane concentrations in the world's atmosphere have ranged between 300 and 400 nmol/mol during glacial periods commonly known as ice ages, and between 600 and 700 nmol/mol during the warm interglacial periods.