I would explain to my DC that historically, these things tend to go in phases:
1) Discovery
2) Awareness
3) Advocacy
4) Political will
5) Plans of action
6) Permanent change
I would use some examples of environmental wins, and how strongly those changes were resisted by powerful interest groups, which required significant public activism to overcome. But as Bostonian said, air quality in the US is better (globally, not so much), US forestation percentage is growing, DDT, lead-based paint, and asbestos are nearly nonexistent, and the ozone layer is in recovery.
We just happen to be in different phases of other environmental challenges, particularly with greenhouse gas production (a complex problem with many contributing factors, where limited permanent change has been accomplished, but still lacking political will in some respects) and the results of hydraulic fracking, which is only barely beginning to touch the awareness of most people.
So, it's important that your DS's generation is educated on these issues and made aware, because they're likely to be involved in the solutions later. But we've faced these kinds of threats before, and we've solved a number of them.
