Green Consumerism is somewhat a broad issue. It would be better to suggest measures if you could specify which aspect(s) of green consumerism you would like to measure.
Seem to be a good topic in current global change aspect. If I understood correctly, Green consumerism refers to recycling, purchasing and using eco-friendly products that minimize damage to the environment. Basically it may need life cycle assessment of the products (May be remotely). Or in contrast, you may see the behavior of intended population regarding their requirement and purchasing of the product group. You may also collect the proportion data (no/volume/price) of the green product. You may also calculate carbon content of the product and their life period. Basically it should revolve around the carbon capturing and saving issue. You may also see, out of the products, how many have green lebelling.
You may find this paper (attached) useful where we synthesized the constructs for measuring consumer perception of 'eco-labeling', which is one dimension of consumer perception of green consumerism.
There was an entire issue in Journal of Advertising devoted to green advertising a handful of years ago. I can't remember the date off hand, but it should be relatively easy to find.