Jul 22, 2026 | written by: Tommaso Ciuffoletti
Every year, the same thing happens. Earth Overshoot Day comes around, and the debate inevitably follows. Some people share it as if it were a final verdict on the planet's future. Others dismiss it as an arbitrary construct: a symbolic date built on models, estimates, and unavoidable approximations. In a way, both sides are right. Overshoot Day is, in fact, an estimate.
There is no hidden counter inside the Earth that, at midnight on July 30, announces that humanity has exhausted the resources available for the year. That date is derived from data, models, and statistical conventions. It shifts slightly from year to year, is recalculated as better information becomes available, and, like any complex indicator, carries a degree of uncertainty.
The more interesting question, however, is another one. If a measurement is not perfect, does that make it useless?
Over the years, we have devoted several articles to Earth Overshoot Day. We have explained what it represents, how it is calculated, and why it should not be read as a prophecy but as a tool for reflecting on the relationship between humanity's demand for resources and the Earth's capacity to regenerate them. In the same spirit, when discussing biodiversity, we asked ourselves what it really means to measure life. We can count species, estimate ecosystems, and develop increasingly sophisticated indicators, yet nature will always remain far more complex than the metrics we use to describe it.
This tension between complexity and simplification is not a flaw in sustainability. It is a feature of every human attempt to understand the world.
Take Gross Domestic Product. No economist would argue that GDP captures everything that makes a society prosperous. It says nothing about happiness, the quality of relationships, the health of ecosystems, leisure time, or the distribution of wealth. Yet we continue to use it because it describes an important dimension of reality and, above all, allows meaningful comparisons across countries and over time.
The same is true of inflation. Each of us could argue that our personal cost of living rises differently from what official statistics suggest. And we would be right. Inflation is calculated using a basket of goods that perfectly reflects no one's actual spending habits. Even so, it remains an indispensable tool for understanding how an economy evolves and for guiding both public and private decisions.
Even the Body Mass Index, or BMI, has long been criticised for its limitations. It does not distinguish between muscle and fat, may be misleading for certain groups of people, and was never designed to describe the health of every individual. Yet it remains one of the most widely used tools in epidemiological research because, when applied across millions of people, it reveals collective trends with good effectiveness.
Life expectancy follows the same logic. No one expects every person to live exactly as many years as the statistics suggest. Yet few indicators tell us more about a society's level of development, health, and well-being.
In every case, we accept a simplification. Not because we ignore its limits, but because we recognise the value of the question that measurement allows us to ask.
Sustainability faces an additional challenge. Most of the phenomena it seeks to describe are invisible. We cannot see carbon dioxide accumulating in the atmosphere. We do not witness, day after day, the gradual loss of soil fertility or the slow erosion of biodiversity. These processes unfold over long periods of time and across vast geographical scales, while our everyday experience is shaped by what happens here and now.
That is why we need indicators. Not because they are perfect, but because they make the invisible visible.
Carbon dioxide equivalent, for example, is an extraordinary simplification. It reduces highly complex chemical, biological, and economic processes to a common metric. Of course, it does not tell the whole story. It cannot capture biodiversity, water quality, the cultural value of a forest, or the resilience of a landscape. Yet precisely because of that simplification, it allows us to compare different activities, define shared goals, and assess whether we are moving in the right direction.
Earth Overshoot Day serves a similar purpose. It does not claim to tell us the exact day on which "the Earth runs out." Instead, it helps us visualise an imbalance that would otherwise be almost impossible to grasp. It turns a highly complex relationship—the balance between the planet's regenerative capacity and humanity's demand for resources—into an immediate image that prompts a simple but profound question: what does it mean to live as though we had more than one Earth?
Of course, no indicator should ever become a dogma. Science does not work that way. Models improve, data become more accurate, methodologies evolve. It is both legitimate and necessary to discuss how these metrics are built, to question their limitations, and to develop better ones.
But there is a fundamental difference between debating a metric and using its imperfections as an excuse to ignore the problem it seeks to describe. Confusing the two would mean giving up one of the most valuable tools we have: the ability to make our impact on the world visible.
Perhaps, then, the true value of Earth Overshoot Day lies not in the precision of its date, but in the question it asks us every year. Our measurements will always be approximations of reality. Reality, fortunately or unfortunately, will always be more complex than any number.
Yet without those numbers, we would risk something even worse: convincing ourselves that whatever cannot be measured does not exist.
In the end, sustainability begins precisely here. It begins with our ability to give a name, a shape, and sometimes even a number to impacts that, for centuries, remained invisible. Not because numbers can tell the whole story, but because they are often the first step towards learning to see it.
