Earth Overshoot Day is the day in the year when our demand for ecological resources and services exceeds what Earth can regenerate in that year. We maintain this deficit by liquidating stocks of ecological resources and accumulating waste, primarily carbon dioxide in the atmosphere.
Earth Overshoot Day is hosted and calculated by Global Footprint Network, an international think tank that coordinates research, develops methodological standards and provides decision-makers with a menu of tools to help the human economy operate within Earth’s ecological limits. There’s more detail here.
What will you be doing to mark this day? In happier circumstances, we might have said “celebrate”.