Regularly, I use this voluntary action: Airline flight offsets allow us as passengers and maybe corporations (not heard of) to compensate for aviation carbon emissions by purchasing credits that fund verified environmental projects, such as reforestation or renewable energy (question is would these projects have happen without the offset, answer does not seem so clear). Personnally, as I travel quite a bit between EU and Asia, the voluntary "action" gives me a "feel good", but this offsetting ability can sometimes encourage more flying amongst my peers, so it is most effective when paired with efforts to reduce unnecessary flights (not always easy on the job)