 The Norwegian central bank on Wednesday excluded four Canadian oil and gas companies from its 1-trillion wealth fund, the worlds largest, for producing too much greenhouse gas emissions, its first use of carbon emissions as a criterion to blacklist firms. Canadian Natural Resources Ltd, Cenovus Energy Inc , Suncor Energy Inc, and Imperial Oil Ltd were excluded from the fund due to unacceptable greenhouse gas emissions, Norges Bank said in a statement The decision was based on recommendations from the Council on Ethics, the funds ethics watchdog, because of the companies carbon emissions from production of oil to oil sands, the central bank said. 