Reutershttp://www.reuters.com/article/environmentNews/idUSTRE51J3VL20090220?feed: Air travelers are paying vastly differing prices to offset their contribution to climate change, in some cases three times market levels, despite efforts to increase transparency in an unregulated market. Under a regulated carbon market, countries and companies buy offsets to help them meet binding international climate targets. Prices have halved in recent weeks as recession reduces industrial output and expected emissions. But prices which consumers pay in an …