Earth Overshoot Day 2018

Today is Earth Overshoot Day! Here’s a little background that will help you understand why today is not a day for celebration, and what you can do about it.

What is Earth Overshoot Day?

Earth Overshoot Day is the day of the year when humanity’s demand for natural resources has exceeded the ability of the earth to renew them. This year it occurs on August 1, the earliest it has ever been.

Earth Overshoot Day is calculated by determining how many days the earth’s biocapacity can support human consumption. The biocapacity can be calculated for any region by totalling the resources available in biologically productive forests, fisheries and crop land. The Ecological Footprint of the same area is calculated by measuring the same region’s demand for those resources. These metrics are then used to calculate the day of the year when the demand exceeds supply with this formula:

(Planet’s Biocapacity / Humanity’s Ecological Footprint) x 365 = 
Earth Overshoot Day

An important thing to remember is that the planet’s biocapacity is the amount of resources that can be sustainably consumed in a year, not the total available resources. By producing a resource deficit we are consuming resources that cannot be replenished before they are harvested again, depleting the overall resources available to us.

The components of an ecological footprint. Image:


Earth Overshoot Day was introduced by Andrew Simms of the New Economics Foundation and Global Footprint Network in 2006, at which point it occurred in October. However, the idea of an ecological footprint was pioneered by Mathis Wackernagel and William Rees at the University of British Columbia in 1990, making way for the footprint movement and the development of other

metrics, like the carbon footprint. Though humans have been altering the natural environment for centuries, our global consumption of natural resources didn’t exceed the planet’s sustainable supply until 1969. Since that year, it has already advanced 5 months, and our global consumption has increased by more than 50%. Earth Overshoot Day is calculated using global biocapacity and consumption estimates, but the same calculations can be done on any scale, from countries to individuals. This year, Overshoot Day in the United States is on March 15, considerably earlier than 2017’s date of June 10.

How Earth Overshoot Day has progressed from 1969 to the present. Image:
How Earth Overshoot Day differs across the globe. Dates earlier in the calendar year signify a large ecological footprint. Image:


Critics are quick to point out the sweeping calculations and assumptions that are made to produce global biocapacity and ecological footprint metrics. Measures of more complex and indirect impacts of resource use, such as soil erosion due to deforestation and conversion to cropland or ecological collapse due to overfishing, are not included because there simply aren’t data available to make those calculations.

I certainly agree that the current numbers used to calculate overshoot days and ecological deficits are estimations, but that doesn’t make them useless. Overshoot days provide an accessible way to present the complexities of ecological deficits to people who might not have confronted their personal footprint yet. The ability to scale ecological deficits to global or individual scales makes them a simple way to compare footprints across regions and communities to support sustainability campaigns around the world. The fact that overshoot days at almost every scale are earlier each year is an undeniable sign that our consumption is unsustainable. It would be counterproductive to argue over accuracy when action is absolutely necessary.

What can you do?

Though global overconsumption is a huge and overwhelming problem, there are steps that every individual can take to make a difference in their own lives and in their communities. Firstly, spread the word! People can’t fix their behavior if they don’t know it’s broken. Tell your family, friends and neighbors what you’ve learned, and share the ways that you are changing your own habits to give them a place to start. Tell your local representative that you care about this issue, and the ways that you expect them to take action to protect your future. Urge them to support sustainability initiatives, make resources available to communities to complete their own projects, and set examples for surrounding areas.

If you want to change your own behavior, but don’t know where to start, the Global Footprint Network has a personal Ecological Footprint calculator that can help ( It asks questions about how you source your food, how you travel and the kinds of goods you buy for yourself and your home to figure out your current consumption. The results include your personal overshoot day and break down your carbon footprint to help pinpoint the most pressing areas for improvement.

Here’s what happened when I tried it!

If everyone lived like I do, Earth Overshoot Day would be on May 16 and we would need 2.7 earths to meet our resource demand. The largest contributors to my personal ecological footprint are my food choices (mostly vegetarian, but not always local so the carbon footprint is high), and transportation (I fly approximately 24 hours per year). At the end of the results they present solutions that address big picture problems, like urban planning and access to family planning tools, as well as small steps that individuals can take every day. Though I probably won’t stop visiting my family across the country, I can definitely be more conscious about my food choices and decrease my everyday carbon footprint in other ways. If each of us were to take steps to decrease our personal overshoot days, we have the power to reverse the trend and reduce our global consumption.

I hope this blog post was a wake-up call to the impact that we all have on the environment on a large scale. Take a moment to absorb the enormity of the problem, then take a breath and get started doing what you can to make positive change!

Liz Allyn

Conservation Made Simple




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