Bloomberg: Canada’s government should double the price companies pay to exceed limits on greenhouse gases because the current cost won’t slow pollution enough, the country’s leading environmental activist groups said. Carbon dioxide and other gases that contribute to global warming should cost at least C$30 ($30) a ton next year, and reach C$75 a ton by 2020, according to a report today co-written by 11 groups. The price could be set by imposing a tax on carbon or through regulations with …