Limits to Growth: The 30-Year Update
Everything else was just looking at elements. Technology is important, for example, but exists within a system. They looked at the system. They had to simplify and assume a lot, which the media didn't understand (probably benign ignorance) and critics blew out of proportion (probably maliciously), but I found their approach the most meaningful.
Sadly, I know many people who care about the environment but don't understand the (relatively simple) math in their approach, and many people who understand the math but don't care about the environment, but almost no one who cares and understands. So in about a decade since reading it, I haven't found anyone I can talk to about it meaningfully.
A great companion by one of the authors is Thinking in Systems by Donella Meadows -- https://www.amazon.com/Thinking-Systems-Donella-H-Meadows/dp....
Both changed my views more than almost any other books.