The head of Shell Oil Co said on Tuesday that governments need to enact mandatory limits on greenhouse gas emissions and not rely on voluntary measures to battle global warming. "I think that voluntary is not fast enough," Shell President John Hofmeister told an environmental event… Many companies have complained that the patchwork of regulations emerging around the globe needs to be replaced by a more uniform system that will create a level playing field for companies to address climate change… Hofmeister said the U.S. Securities and Exchange Commission should adopt rules currently under consideration that would require companies to disclose their carbon emissions to investors.