It’s more of a symbolic day than a scientific one – it’s impossible to put an exact date to it, but it’s an annual reminder that our current levels of consumption simply cannot continue forever.
Demands for food and fish, wood, and CO2 absorption are running higher than the earth can provide at a sustainable level. Globally, these resources and services would require 1.3 to 1.5 earths to supply in the longer term. The Footprint Network explains why it is possible to overshoot in this way:
The fact that we are using (or “spending”) natural capital faster than it can replenish is similar to having expenditures that continually exceed income. In planetary terms, the results of our ecological overspending are becoming more clear by the day. Climate change – a result of carbon being emitted faster than it can be reabsorbed by the forests and seas – is the most obvious and arguably pressing result. But there are others as well: shrinking forests, species loss, fisheries collapse and freshwater stress to name a few. The environmental crises we are experiencing are all symptoms of an overall trend—humanity is simply using more than the planet can provide.