Too many people consuming too many resources and generating too much waste: that’s why humanity keeps pushing deeper into ecological overshoot. On Earth Overshoot Day, let’s not forget the P factor. 

by Lucia Tamburino & Philip Cafaro

Every year on Earth Overshoot Day, a table like the one below makes the rounds, showing the number of Earths needed to be ecologically sustainable if all the people in the world had the same ecological footprint (EF) as the average citizens of various countries. This is computed by fixing the world population at the current value and varying the per capita ecological footprint. From Table 1, we see that if people around the world lived as in India, we would only need 0.72 Earths to be sustainable, while if people on average lived as in Norway, we would need 3.4 Earths. The message is clear: high consumption levels drive ecological unsustainability.

But high per capita consumption is only half the story. The other half, of course, is the number of people doing the consuming. To highlight this, Dr. Tamburino built a different table, fixing the per capita EF at the current world average (2.75 global hectares per person) and varying the population. This allows her to show the number of Earths that would be needed for humanity to live sustainably if the entire world was as densely populated as India, Norway, or various other countries (see previous blog for methodological details). The results, displayed in Table 2 below, demonstrate that high population levels also undermine sustainability.

Taken together, Tables 1 and 2 provide a more complete picture of the world than either one alone. Combined, they highlight the two main drivers of ecological overshoot: excessive average resource consumption and excessive numbers of consumers. Some countries err more in one direction, some more in the other, while some have managed to keep their numbers and demands in line with what the Earth can actually sustain.

Countries can be unsustainable even if their per capita footprints are low (like India) and sustainable even if their per capita footprints are high (like Norway). This is shown by a world map at the Global Footprint Network website, depicting all the countries of the world in green or red, depending on whether they are living within their national biocapacities (Figure 1 below).

Looking at this map, we see that both India and France are among the unsustainable countries: India because of its immense population and France because of its high per capita consumption level. The United States is also deep red, driven by both high average consumption and the third largest population in the world. On the other hand, much of Scandinavia, South America and Africa are green, indicating that these countries are living within their biological means, at least for now.

Sweden has a higher average EF than France, yet on the map it’s green, since it remains relatively sparsely populated. If the whole world was as densely populated as Sweden, less than 1.3 billion people would inhabit the planet and the world would be sustainable without any need for reducing the average EF. Similarly, Brazil is deep green, a function of relatively low per capita consumption combined with large, undeveloped, biologically productive areas in the Amazon that reduce its overall population density.

Table 3 below compares seven large nations in terms of population density, EF and overall sustainability. The unpopularity of reduced consumption and the imperative to develop in poorer countries strongly suggest that substantial population reductions must be part of creating sustainable societies in all of these nations, and in the world as a whole. Note: not ending population growth, but substantially reducing current populations.

Dr. Tamburino is creating an interface that allows people to see how population numbers and consumption levels impact ecological sustainability. We invite you to explore it. At one link, you can see what the global population would be if the whole world were as densely populated as your home country, or any countries you’re interested in (Figure 2 below). You can also see how many Earths would be necessary to sustain that global population, either at those countries’ average EF or at the current global EF.

At another link, you can vary both global population density and global EF to see how different combinations impact ecological sustainability (see below). Doing so brings home the point that on a finite planet, increasing our numbers limits how much we can consume as individuals, just as increasing our average consumption limits the numbers of people we can realistically expect the Earth to support. Figure 3 below shows the results for Earth’s current population density and average per capita EF, showing that we are indeed deep into “overshoot” mode. This year, Earth Overshoot Day arrives on August 22.

As humanity trashes our home planet, some environmentalists continue to insist that overconsumption is the problem, not overpopulation. Time’s up on that innumeracy, the equivalent of arguing that “it’s really the length, not the width” that determines the area of a rectangle.

Besides, we need to get real about how much we and our fellow citizens are willing to decrease our consumption. A global population of 7.8 billion would need to decrease its average EF to about 1.65 gha per capita to live within Earth’s biocapacity, a level currently achieved only by poor countries that few people see as appealing models for the future. With Earth Overshoot Day coming more than four months before the end of year, it seems clear that we must address both drivers of unsustainability to have any hope of preserving a habitable Earth for future generations.

For more discussion of Earth Overshoot Day and population, see Karen Shragg’s “Every Day is Overshoot Day” and Dave Gardner’s new podcast “Damn, It’s Earth Overshoot Day Already!”