The Human System is within the Earth System. They should be modeled bidirectionally coupled, as they are in reality. The Human System is rapidly expanding, mostly due to consumption of fossil fuels (approximately one million times faster than Nature accumulated them) and fossil water. This threatens not only other planetary subsystems but also the Human System itself. Carrying Capacity is an important tool to measure sustainability, but there is a widespread view that Carrying Capacity is not applicable to humans. Carrying Capacity has generally been prescribed a priori, mostly using the logistic equation. However, the real dynamics of human population and consumption are not represented by this equation or its variants. We argue that Carrying Capacity should not be prescribed but should insteadbe dynamically derived a posteriori from the bidirectional coupling of Earth System submodels with the Human System model. We demonstrate this approach with a minimal model of Human–Nature interaction (HANDY).

人类系统在地球系统之内。实际上，应该对它们进行双向耦合建模。人类系统正在迅速扩展，这主要是由于消耗了化石燃料（比大自然积累化石燃料快一百万倍）和化石水。这不仅威胁其他行星子系统，而且威胁人类系统本身。承载能力是衡量可持续性的重要工具，但是人们普遍认为，承载能力不适用于人类。承载能力通常是事先确定的，大多使用逻辑方程。但是，该方程式或其变体不能代表人口和消费的真实动态。我们认为，不应规定承载能力，而应从地球系统子模型与人类系统模型的双向耦合中动态得出后验。我们用人与自然互动的最小模型（HANDY）演示了这种方法。