Nate Hagens defines 'biophysical reality' as the framework within which all human activities and economic systems are fundamentally constrained and driven by the principles of biology and physics. He emphasizes that this concept underscores the finite nature of Earth's resources and the ecological limits that govern energy flows and material cycles. Hagens articulates that understanding biophysical reality is crucial for recognizing the interdependence of human well-being, ecological health, and the sustainable use of natural resources. He highlights that economic growth and technological advancement cannot transcend these physical laws, and a failure to acknowledge this reality will lead to societal and environmental consequences. In his view, the future trajectory of humanity hinges on aligning our lifestyles and energy consumption with the immutable constraints imposed by the biophysical world.

See also: climate model, ecological footprint, renewable energy, fossil energy, nuclear power