The last unit of the class finds us considering the options for avoiding, or "mitigating," a human impact on Earth's climate. Bottom line: I think it would be a challenge that humankind could beat if we decided to. If there hypothetically were no more coal on Earth, our potential to alter the climate would be much less. Finding energy sources in that world would not be an existential threat would just be a business opportunity. The hard part, in my opinion, is making that decision.