photo: Luis Markovic/CC BY
Every year towards the end of summer the folks at the Global Footprint Network release their calculations on when Earth Overshoot Day will be for the year. In 2011, September 27th is the day when humanity as whole begins using more resources than the planet can perpetually regenerate annually. We've covered this, as it were, event a number of times, so check out what was written in 2008, 2009, and 2010 for some context.
As for a more basic definition of what Earth Overshoot Day is, and why it's critically significant--if not as a day itself, but conceptually--here's what the Global Footprint Network says:
For a vast majority of human history, humanity has used natures' services - to build cities and roads, to provide food and create products; and to absorb the CO2 generated by human activities - at a rate that was well within the means of what nature could regenerate. But, sometime in the mid 1970's, we crossed the critical threshold. Human demand on nature began outstripping what it could renewably produce, a condition known as ecological overshoot.
Global Footprint Network's preliminary 2011 calculations show we are now using resources at a rate that would take between 1.3 and 1.5 planets to sustainably support. Our research shows us on track to require the resources of two planets well before mid-century.
Put simply, Earth Overshoot Day shows the day on which our total Ecological Footprint (measured in global hectares) is equal to the biocapacity (also measured in global hectares) that nature can regenerate in that year. For the rest of the year, we are accumulating debt by depleting our natural capital and letting waste accumulate.
As for the variations in date (2010 was over a month earlier than previous calculations), the Footprint Network last year stated that rather than being a marked increase in consumption, results from variations in accuracy of available data.
Remember though, as the graph above shows, the trend is solidly upwards, resulting in no small part from increases in consumption levels and increases in human population.