The planetary boundaries are nine areas that represent a “safe operating space” for humanity. We have crossed six of them. This page offers a basic breakdown of each boundary to help those not trained in earth science understand what they mean.
The physical status of the Earth since the last ice age has allowed human beings to flourish. Because the average global temperature was relatively stable for those 10,000 years, we were able to begin to settle down and grow our food rather than moving from place to place to hunt and gather it. It was this ability to settle that encouraged the growth of knowledge, ideas, and technology. However, once we figured out how to extract and burn fossil fuels and industrialize agriculture, humans became a major driving force of change on our planet.
In 2009, a group of 29 scientists came together to propose that nine key areas ensure a safe operating space on Earth—the planetary boundaries. The idea behind the boundaries was to look at the safe and stable Earth systems that had existed for the last 10,000 years but were now being thrown out of equilibrium by human activities.
The scientists from that 2009 paper argued that humanity was risking irreversible and catastrophic changes if we continued down our current path and that we had already crossed the boundary for three of those systems. Today, all nine of the boundaries have been quantified and analyzed, and we have now passed six of them.
Source: Stockholm Resilience Center, 2023
Source: Richardson et al., 2023
<aside> 📌 TL;DR: More of the sun’s energy is getting trapped at the Earth’s surface, leading to an enhanced warming effect. Higher radiative forcing = more trapped energy.