Today is not a day to be celebrated, but it is a day that deserves to be noticed and (hopefully) acted upon.

It is the day in which the Earth goes into "overshoot."

Earth Overshoot Day is the day calculated by the Global Footprint Network (GFN) on which the Earth goes into debt, or more specifically we go in debt to the Earth. Every year the Earth is capable of producing a finite amount of natural resources — trees and wetlands to absorb carbon, agricultural lands to raise produce and livestock, trees to make paper, and so on.

When we exceed the naturally replenishable allotment of resources, we are forced to deplete resource stocks that will produce next year's crops and carbon banks.

It's pretty easy to figure out the downward spiral here.

The more we tap into those foundational resources, the less we are able to produce the following year. And then add that to steadily increasing consumption in countries like India and China ... you get the picture.

Unless we have a radical intervention, we are headed for a collision course of epic proportions that can have only one of two results — the increasing scarcity (and costs) of resources resulting in a breakdown of the economic system and an end to the cycle of ever-expanding consumption. Or worse, the complete collapse of the complex natural systems that (until the 1970s) actually met all of our annual needs.

According to updated calculations by the GFN, Earth has been going into overshoot since at least 1970. It began with a relatively modest overshoot, just a couple of days. But ever since, Earth Overshoot Day has typically crept forward several days each year (with an explosive increase in the mid '90s to the mid 2000s). It fell on Dec. 23 in 1970, and by 1973 it had already leapt forward a full month. It was up to Oct. 13 by 1990, Oct. 4 in 2000, and Aug. 28 in 2010.

The human population currently requires about 1.6 Earths worth of resources. But the demand that pushes us into overshoot is not evenly distributed. The United States is one of the biggest culprits — if everyone in the world consumed as much as the U.S., we'd need roughly four planets worth of resources, according to the GFN.

Earth Overshoot DayReduced CO2 emissions could help push back the date of Earth Overshoot Day. (Image: GFN)

So what can we do?

For starters, we need to wake up to the facts. Global warming is not the only problem we have to worry about. Though it is important, the geopolitical and economic repercussions of a world in which essential resources like water and food are unavailable may be even more urgent. And, of course, those kinds of problems are only growing worse due to climate change.

Post wake-up, everyone — especially those of us in countries with large carbon footprints — needs to go on a low-carbon diet. Renewable energy is becoming more affordable and world leaders are starting to make strides in phasing out fossil fuels, but each person on Earth can help in the meantime. As the graph above suggests, it's not too late to send Earth Overshoot Day back toward the end of the calendar.

If you want to measure your own environmental footprint, try this footprint quiz.

Note: This story was originally written in 2009 and has been updated to reflect 2015 data.

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