Apple can claim that they're a green, sustainable company all they want, but if they're called upon to back that claim up they should be required to be more transparent about it. There are customers that buy products based upon the company behind them, and if a company is claiming they are something that they are not, then that is akin to false advertising.
I am actually happy that Apple's Tim Cook picked a fight with climate change deniers. This is a subject that needs to be addressed yesterday. We have to aim for more sustainability, otherwise our planet is going to become inhospitable. This isn't up for discussion. The scientific consensus is in.
Big corporations contribute hugely to climate change and they're the ones that can make a difference. It shouldn't be just climate change as to why companies should be more transparent, but companies have in the past and still today effect people's health, especially with the ways that their toxic waste is disposed of.
Even though they are public companies they are still driven by the need to provide maximum value for the shareholders so I don't really see the need to require public companies to be more transparent about their sustainability efforts, I think it's good for public relations if they do but I don't think it should be a requirement.
I am not sure what exactly it would entail to be more transparent about sustainability efforts, but companies who are going this route are probable eager, anyway, to be marketing and publicizing their earth friendly efforts. To make it a requirement goes too far, especially for companies who are notmaking these efforts.