Recently, I was covering food miles with a rather high level class and made this PPT to serve as an introduction to the topic. This was followed by other activities but the students seemed to find this intro very interesting and ended up really enjoying the class.
This class have a fairly high level so hence the vocab in the PPT is a little more complex, and I use it to revise some words the had been reviewing recently such as "environment" and "impact" but please don't hesitate to edit anything to make it more suited to the level of your students.
With higher level classes, it is possible to get the students to have a discussion about the topic afterwards. For lower level classes, I usually include a worksheet and allow them to discuss their opinions in Japanese.