Identify your issue. Talk to people in your community about what environmental issues affect them. Find a popular article on your topic. Look in newspapers, magazines, blogs, websites, etc. to identify and find background information about relevant issues.
Narrow your topic. If you’re considering a few different issues, pick one. Make sure it is very specific, or choose one sub-component of your issue.
Research the issue. Find articles from the scholarly scientific literature to understand the causes and effects of the issue. This may require the bulk of your time.
Expand your understanding of the issue by finding scholarly sources from other disciplines, including economics, sociology, political science, law, education, etc. to better understand the broader implications of the issue from other disciplinary perspectives.