LESSON: What day is Earth Overshoot Day?

The purpose of this activity is to understand the concepts and metrics of Ecological Footprint and biocapacity, and why addressing ecological resource constraints is essential to global sustainability.

Appropriate for: 6th Grade – 12th Grade
Standards for: 6th Grade, 7th Grade, 8th Grade
Prep Time: 15 minutes
Activity Time: 120 minutes
Subjects: Analyzing & Interpreting Data, Earth & Space Science, Obtaining & Evaluating Information, Geography, Maths

Connections to the Next Generation Science Standards

NGSS Disciplinary Core Ideas (Grades 6-8)
MS-ESS3.C: Human Impacts on Earth System
Science and Engineering Practices (Grades 6-8)
Defining and Delimiting Engineering Problems

About this lesson

Students will have the opportunity to discover and browse the open data platform Ecological Footprint Explorer, interact with data, learn about “nowcasting” and statistical trends. They will also devise the methodology to estimate the date of Earth Overshoot Day 2021.

Essential Questions

  1. What does the Ecological Footprint measure?
  2. What does biocapacity measure?
  3. How is it possible for humanity to consume as much ecological resources as if we lived on 1.7 planets?
  4. Has the increase of the global ecological deficit been accelerating or slowing down over the past few years?

Learning Objectives

Students will learn that the minimum threshold for sustainability (supply and demand of natural resources) can be measured and turned into useful data.

Looking at some specific country data chosen by their teacher, they will learn that consumption per capita varies country by country.

They will also have the opportunity to look at climate change and GHG from a unique angle: they will discover that carbon emissions make up the largest component of the Ecological Footprint (globally and in most countries), and will start thinking of carbon emissions in relation to the area of forestland required to absorb them.


Computer lab with one computer for two students at least (computers should have Internet access) + one computer that the instructor can project from.

Teacher's Prep

It is essential for the teacher to master these concepts beforehand:

  • Sustainability: the ability of a system to last or endure; meeting current human needs without endangering our descendants
  • The Ecological Footprint measures the amount of biologically productive land and sea area required to provide for the demand of population, including the the areas for growing the food, fiber, and timber they consume, the space they occupy with their houses and roads, the area needed to sequesters the carbon dioxide from burning fossil fuel.
  • Biocapacity is the biologically productive area that provides renewable biological capacity including the replenishment of resources and the absorption of waste such as carbon dioxide from burning fossil fuel.
  • Ecological overshoot occurs when human demand exceeds the regenerative capacity of a natural ecosystem. Global overshoot occurs when humanity demands more than what the biosphere can renew. In other words, when humanity’s Ecological Footprint exceeds what the planet can regenerate.
  • Earth Overshoot Day marks the date when humanity’s demand for ecological resources (fish and forests, for instance) and services in a given year exceeds what Earth can regenerate in that year. We maintain this deficit by liquidating stocks of resources and accumulating waste, primarily carbon dioxide in the atmosphere. Andrew Simms originally conceived the concept of Earth Overshoot Day while working at the UK think tank New Economics Foundation.
  • Global hectares are hectares of biologically productive land and sea area with world average bioproductivity. Both biocapacity and the Ecological Footprint are measured in global hectares. (A hectare contains 10,000 square meters and corresponds to about 2.47 acres.)

Suggested Lesson Plan

PART 1: Introduction or refresher: what is sustainability?

Ask students what sustainability means to them, and write it on the board.

Zero in on the concepts of consumption, demand, renewable natural resources (also called biological or ecological resources), the carrying capacity of natural ecosystems.

Introduce the terms “Ecological Footprint,” “biocapacity,” “ecological deficit” or “overshoot”.

PART 2: Watch the video

PART 3: Field students’ questions about the video

What did they understand? Guide the discussion and help clarify or explain what they did not understand.

PART 4: Math activity: how do we go about calculating the date of Earth Overshoot Day 2020?

If possible, gather the students in groups of 3 or 4 to devise the correct approach.

Have each group present their conclusions to the class.


Finalize the methodology and result with the whole class.