What is a blocker? A blocker is somebody who gets in the way of progress for an initiative.
You may be surprised to learn who the biggest blocker is in your organization. Companies, like every other group of people, have interesting dynamics. Over time departments and organizations as a whole tend to develop unique personalities. Sometimes these personalities serve an individual group but not the company as a whole. When your company starts to develop and execute against a sustainability plan you will become painfully aware of whom the blockers are in your organization. Each one will need to be persuaded but all will require different information.
Let's start at the top. If the CEO or VP of Marketing is resisting the company's efforts to become more sustainable you should focus on the big picture. Look at competitors and see if they are getting free PR for their sustainability efforts. See if they are attracting better employees or maybe they are getting support from local government agencies. All the above have value and are sought after by executives. If the CFO isn't on board there is one great way to get his or her attention - find ways to save money. Make a deal that any money you save on initial sustainability efforts can be redirected to more costly future sustainability efforts. If employees are dragging their feet then make sure that the highest levels of the organization are being as visible as possible in their efforts. Literally ask the CEO to take out the trash; even better have the CEO pull out and sort items that aren't in the correct recycling bins.
Anyone who makes an extra effort should be acknowledged in public. If some are still resisting then introduce some friction into the system (see blog post "Its Just Too Easy NOT to Conserve"). Ultimately if any one person in the chain doesn't do his or her part then the whole system will fail. Think of the wasted effort in the following scenario: you get permission to switch to a more environmental trash hauler, reconfigure the office for recycling bins, train employees on virtues and mechanics of recycling only to find out that the cleaning crew just dumped all the different recycling bins into the trash.
So far we have discussed employees but what about vendors that are out of your control such as landlords? If you don't own your own building like most of us your options could be limited. Your landlord may stop you from installing solar panels or from switching to more efficient lighting. Vendors can be a big barrier to your progress, or maybe not? After doing this for a couple of years (and I am not an expert by any definition) I could identify 50 to 100 actionable items in almost any office I walk into so don't let those two items your landlord won't agree to stop you from doing the other 98. Don't get stuck on a single item. Don't let your biggest blocker - YOU - get in the way!