Q: How do I write a problem statement or a research question if I don't yet know what interests me the most?

By the way you framed your question, it seemed you are not sure what interests you in your research area. However, on a closer read, we see you are interested in environmental issues, but are just not sure how to go about choosing a particular topic for research. If so, that’s a somewhat smaller challenge. :-)

Anyway, it seems your challenge is around finding both a novel and a relevant topic to study. If so, you should begin by undertaking a literature search of current studies related to your specific field/area. Going through these, you will come across the varied issues they cover, and more importantly, what gaps they leave or what limitations they have, which you can then look to possibly exploring through your research. So, here’s an article on conducting effective literature searches that you will find useful: Tips for effective literature searching

Also, there are ways to identify research gaps and arrive at a relevant research question. You may find out more through these resources:

• Don't know where to start? 6 Tips on identifying research gaps
• How to choose a research question

Once you have arrived at your research question is when you need to begin developing a problem statement, for which you will find this resource helpful: The basics of writing a statement of the problem for your research

Hope all this helps you begin moving forward. All the best!