Guardian: Shell warned environmentalists and ethical investors yesterday that failure to exploit tar sands and other unconventional oil products would worsen climate change because it would lead to the world burning even more carbon-heavy coal. Jeroen van der Veer, Shell’s chief executive, said the world needed every kind of energy source it could find at a time of soaring demand. He said groups that had threatened to organise a ban on alternative fossil fuels should be careful because without …