You've heard of energy—but do you have any idea what exergy is?

On today's astounding episode of Planet: Critical, scholar Tânia Sousa explains the concept of exergy—the quality of energy—and why it is critical to understanding our energy systems, our economies, and energy transitions. She explains energy degradation, energy efficiency, and the how differences in available energy actually create the necessary gradients for life to happen. What this means, however, is that the pockets of high quality energy deposits around the world are a gift—and when we go through them, by burning all the oil or mining all the mines, then we will find ourselves in a world where we are capable of doing much less useful work.

Planet: Critical is approaching its five year anniversary, and yet this conversation felt like the very beginning of this journey, when every episode was a revelation. And so it feels important to end the year with this mind-blowing hour. Happy festivities to one and all. See you in 2026.

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