Volcanoes produce much less CO2 than humans. But back on topic. I think the biggest problem facing humanity today is our inaction concerning long term issues. We don't try to solve a problem until it is right in front of us. Most act like they care for long-term issues, but they won't act. Nobody is willing to confront difficult issues before they bring the pain. But I will say overpopulation.
Then why is the lander in images of the moon? Why are there reflectors on the moon? Also, the Astronauts did not receive so much radiation, less than the United States Atomic Energy Commissions' standards.
Enceladus would be far better than Europa concerning radiation and ocean access. You would have to drill through a few kilometers of ice on Europa. But, I think it may be a better location in the oceans than on Enceladus.