There are any number of actions Starbucks could take, but out of the control process, the customer validation and testing step will likely be the most important. In any situation, verifying the voice of the customer is necessary.
When Starbucks attempts to reduce its carbon footprint by removing paper cups from stores, it would do best to phase them out. So as not to alienate customers who aren’t ready for the switch, it could consider increasing its discount for using reusable cups or perhaps offering a more recyclable alternative. This would give it more time to transition away from paper cups while also making a concerted effort to reduce the number it currently uses, all the while maintaining its current customer base.
In the end, there may be a financial benefit for the company, especially if it transitions to primarily reusable cups. By doing this, it would not only help the environment but also no longer need to purchase millions of paper cups annually. Additionally, there would also be a morality benefit for the company itself, which would give it credit and appreciation in the eyes of environmentally conscious customers.