"The Software may not be used in applications and services that are used for or aid in the exploration, extraction, refinement, processing, or transportation of fossil fuels.

The Software may not be used by companies that rely on fossil fuel extraction as their primary means of revenue. This includes but is not limited to the companies listed at https://climatestrike.software/blocklist"

I am not a trained lawyer but that seems pretty easy to understand to me, and has less ambiguity than some other open-source licenses I've read.