One of the gravest challenges humankind will face in the 21st century is the challenge of forging a new relationship with the natural world. Throughout history, people have treated the environment as an unlimited, self-sustaining, and cost-free resource. Historically, humanity's ecological footprint has been small.
However, in recent decades, population growth, increased consumption, and related factors have placed great stress on our planet. In 1960, the world population totaled about 3 billion people. This population has now more than doubled to an estimated 7.2 billion people, with a projected increase to over 9 billion people by 2050. Some of the drivers of this growth are scientific discovery and technological advances that result in reduced infant mortality and greater longevity.
The current level and nature of human activity is not sustainable and, if not changed, will have dire consequences for future generations. This encroaching problem has led to a call for action from a diverse coalition of social actors, known as the sustainability movement.
Sustainability implies meeting current human needs in a way that preserves natural capital for future generations.
The term natural capital refers to natural resources (e.g., air, water, soil, energy) and natural services (e.g., processes of nature such as air and water purification) that keep us and other species alive and support our economies. Current levels of human activity are rapidly depleting natural capital. For example, in 1960, humanity's ecological footprint was estimated at 50% of the earth's capacity. Shortly after 2000, humanity's global footprint was estimated at 125% of the earth's capacity and is projected to be 200% (twice the world's capacity) by 2050. Symptoms of this depletion include increased air and water pollution, global warming, aquifer depletion, declining ocean fisheries, shrinking forests, shrinking wildlife habitats, and species extinction.