I love that analogy. No, you're not going to personally save the world by reducing your carbon footprint. But you know what you are going to be? One leaf on a tree in a forest, making that little bit more oxygen that helps collectively make the world a better place.
And that's worth doing. Especially if you can encourage other people to be leaves too.
I feel we need inverse buddhism: instead of "compassion to the world", which required a huge imagination effort in the times of Buddha, we are now overflowed with the vision of the world's suffering and we need re-align our compassion with the other fields that matter: the portion of the world we can act upon and that can act upon us.
You are not going to stop the bombs that are right now flying towards people. But you are going to receive the news of the suffering they cause, and if you are even slightly empathic, you will feel the pain of the people these bomb will make grieve.
What matters is that you can make good where you are. Don't be ignorant of the world's pain, but protect yourself.
The world just grew its nervous system and it fires its pain receptors like crazy. Do what you need to stay sane.