Sustainability is an ecological concept that refers to a system's ability to maintain itself and remain productive. An ecosystem is the complete set of living and nonliving components of a particular area. Ecosystems can remain relatively constant for long periods, or they can change rapidly. An ecosystem that changes rapidly transforms into a completely different type of environment, with different members, different energy flow, and different productivity. Though this happens all the time in nature, human societies frequently find this abrupt change of living conditions disturbing and difficult to live with. Sustainability has come to refer to attempts to maintain environmental conditions that will allow humans to live and thrive long into the future. It is a key component of modern environmental planning.
For much of human history, people have not given much thought to their impact on the environment. Humans have moved into new areas, killed animals for food, and transformed the landscape with agriculture. This has always caused changes to ecosystems, many of which never again function as they did before humans arrived. Thousands of animal species have gone extinct due to human hunting and building. Soils and waters everywhere have been transformed.
All living organisms affect their local environments. Any kind of animal can transform a landscape. However, humans have made so many changes so fast that other natural evolutionary processes cannot keep up.
Until the early 2000s, this human impact on environment was not thought by many people to be a problem. Much of Earth's land was uninhabited by humans, so people could move into new areas when the areas in which they lived became crowded or land became unproductive. Societies have occasionally collapsed due to environmental devastation, but people have always carried on.
In the late twentieth century, however, environmentalists and ecologists realized that human actions on nature were proceeding so rapidly and with so much power that Earth's living systems were being changed radically. Humans depend on natural systems for all aspects of life. Plants are the main source of oxygen in air. Freshwater is essential for human existence. Soil is necessary for agriculture. All of these necessities are the result of naturally functioning ecosystems. Ruining those ecosystems—through pollution, consumption of fossil fuels, habitat destruction, and introduction of non-native species—could lead to large-scale collapses.
Sustainability is thought to be the answer to runaway development and rapid population growth. Traditional development has focused on human economics and society, while ignoring environmental costs. Sustainable development considers the environment as an important component of all planning. It assumes that the environment is just as significant as economics and social desires. Sustainable growth is meant to allow people to live well and to continue to improve their lives, without using up irreplaceable resources and causing so much environmental destruction that humans themselves are harmed.
There are various approaches to sustainability. The U.S. Environmental Protection Agency (EPA) has outlined several aspects of sustainability. Key elements include a focus on clean energy, clean automobile technology, improved air quality, energy-efficient building, clean water, and attention to the health of ecosystems. International and local organizations everywhere are addressing the same concerns.
Whether any of this will help is open to question. Some experts believe that the human population (over 7.1 billion as of 2014) is already beyond Earth's carrying capacity, an ecological measurement of how many organisms can live in an ecosystem. Biodiversity has dropped and continues to fall. Air and water quality have both changed drastically since humans began using fossil fuels such as coal and petroleum. Sustainability may require significant changes in how humans live, with drastically reduced consumption.