An environment is a complex of external factors. It acts on a system and determines its course and form of existence. Generally, the environment or milieu of some object, action, or individual consists of the substances, circumstances, objects, or conditions by which the object or person is surrounded or in which the action occurs.

An environment may be thought of as a superset, of which the given system is a subset. An environment may have one or more parameters, physical or otherwise. The environment of a given system must interact with that system in order for it to sustain and develop.

Although the two terms are interchangeable, some disciplines prefer the term milieu to avoid confusion with the more widely used meanings of environment in ecology, politics, and sociology. Either word may be used with specialized meaning in various contexts.

Natural Environment

The natural environment comprises all living and non-living things that occur naturally on Earth. In its purest sense, it is thus an environment that is not the result of human activity or intervention. The natural environment may be contrasted to "the built environment."

For some, there is a difficulty with the term "natural environment" in that nearly all environments have been directly or indirectly influenced by humans at some point in time. In order to address this concern, some level of human influence is thus allowable without the status of any particular landscape ceasing to be "natural." The term's meaning, however, is usually dependent more on context than a set definition. Many natural environments are the product of the interaction between nature and humans. For this reason, the term ecosystem has been used to describe an environment that contains nature, and includes people. It follows then that environmental problems are human or social problems. Some also consider it dangerously misleading to regard "environment" as separate from people.

It is the common understanding of natural environment that underlies environmentalism - a broad political, social, and philosophical movement that advocates various actions and policies in the interest of protecting what nature remains in the natural environment, or restoring or expanding the role of nature in this environment.

While wilderness is increasingly rare, wild nature (e.g., unmanaged forests, uncultivated grasslands, wildlife, wildflowers) can be found in many locations previously inhabited by humans.Goals commonly expressed by the environmentalists include: reduction and clean up of man-made pollution, with future goals of zero pollution; reducing societal consumption of non-renewable fuels, development of alternative, green, low carbon or renewable energy sources; conservation and sustainable use of scarce resources such as water, land and air; protection of representative or unique or pristine ecosystems; preservation and expansion of threatened or endangered species or ecosystems from extinction; the establishment of nature and biosphere reserves under various types of protection, and, most generally, the protection of biodiversity and ecosystems upon which all human and other life on earth depends.

More recently, there has been a strong concern about climatic changes caused by anthroprogenic releases of greenhouse gases, most notably carbon dioxide, and their interactions with human uses and the natural environment. Efforts here have focused on the mitigition of greenhouse gases that are causing climatic changes (i.e., through the Climate Change Convention and the Kyoto Protocol), and on developing adaptative strategies to assist species, ecosystems, humans, regions and nations in adjusting to these climatic changes.

Built Environment

The term built environment refers to the human-made surroundings that provide the setting for human activity, ranging in scale from buildings and parks or green space to neighborhoods and cities that can often include their supporting infrastructure, such as water supply, or energy networks. The built environment is a material, spatial and cultural product of human labor that combines physical elements and energy in forms for living, working and playing. It has been defined as “the human-made space in which people live, work, and recreate on a day-to-day basis”. The built environment encompasses places and spaces created or modified by people including buildings, parks, and transportation systems. In recent years, public health research has expanded the definition of "built environment" to include healthy food access, community gardens, walkabilty, and bikability.

Early concepts of built environment were introduced thousands of years ago. Hippodamus of Miletos, known as the "father of urban planning", developed Greek cities from 498 BC to 408 BC that created order by using grid plans that mapped the city. These early city plans eventually gave way to the City Beautiful movement in the late 1800s and early 1900s, inspired by Daniel Hudson Burnham, a reformist for the Progressivism movement who actively promoted a reform of the landscape in tandem with political change. The effort was in partnership with others who believed that beautifying American cities would improve the moral compass of the cities and encourage the upper class to spend their money in cities. This beautification process included parks and architectural design.

Currently built environments are typically used to describe the interdisciplinary field that addresses the design, construction, management, and use of these man-made surroundings as an interrelated whole as well as their relationship to human activities over time (rather than a particular element in isolation or at a single moment in time). The field is generally not regarded as a traditional profession or academic discipline in its own right, instead drawing upon areas such as economics, law, public policy, public health, management, geography, design, technology, and environmental sustainability. Within the field of public health, built environments are referred to as building or renovating areas in an effort to improve the community’s well-being through construction of aesthetically, health improved, and environmentally improved landscapes and living structures.


Environmentalism is a broad philosophy, ideology and social movement regarding concerns for environmental conservation and improvement of the health of the environment, particularly as the measure for this health seeks to incorporate the concerns of non-human elements. Environmentalism advocates the preservation, restoration and/or improvement of the natural environment, and may be referred to as a movement to control pollution or protect plant and animal diversity. For this reason, concepts such as a land ethic, environmental ethics, biodiversity, ecology and the biophilia hypothesis figure predominantly.

At its crux, environmentalism is an attempt to balance relations between humans and the various natural systems on which they depend in such a way that all the components are accorded a proper degree of sustainability. The exact measures and outcomes of this balance is controversial and there are many different ways for environmental concerns to be expressed in practice. Environmentalism and environmental concerns are often represented by the color green, but this association has been appropriated by the marketing industries and is a key tactic of greenwashing. Environmentalism is opposed by anti-environmentalism, which takes a skeptical stance against many environmentalist perspectives.

Timeline of Environmental Events

More Timelines of Environmental Events

The timeline lists events in the external environment that have influenced events in human history. This timeline is for use with the article on environmental determinism. For the history of humanity's influence on the environment, and humanity's perspective on this influence, see timeline of the history of environmentalism.

All About the Environment   National Geographic

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In the News ...

Research reveals how the same foods create markedly different environmental impacts   PhysOrg - May 31, 2018
Researchers at Oxford University and the Swiss agricultural research institute, Agroscope, have created the most comprehensive database yet on the environmental impacts of nearly 40,000 farms, and 1,600 processors, packaging types, and retailers. This allows them to assess how different production practices and geographies lead to different environmental impacts for 40 major foods.

Controversial gas from Peruvian Amazon arrives in UK   BBC - March 4, 2017
A tanker docking in the UK is transporting a controversial cargo of gas from the Peruvian Amazon. It is thought to be the first shipment to the UK from the Camisea project in rainforest 60 miles from Machu Picchu. Supporters of fracking say the UK should frack its own gas, rather than importing from sensitive regions like the Amazon. But opponents of fracking say the practice creates disturbance and pollution and fuels climate change. The tanker Gallina, owned by Shell, is scheduled to arrive at the Isle of Grain in Kent. The gas project at Camisea field has been hugely contentious.

  This Is What Nature Does To Your Body   Seeker - December 1, 2016

Ancient global cooling gave rise to modern ecosystems   PhysOrg - September 27, 2016
Around 7 million years ago, landscapes and ecosystems across the world began changing dramatically. Subtropical regions dried out and the Sahara Desert formed in Africa. Rain forests receded and were replaced by the vast savannas and grasslands that persist today in North and South America, Africa and Asia. Up to now, these events have generally been explained by separate tectonic events - the uplift of mountain ranges or the alteration of ocean basins - causing discrete and local changes in climate. But in a new study, a team of researchers has shown that these environmental changes coincided with a previously undocumented period of global cooling, which was likely driven by a sharp reduction in atmospheric carbon dioxide.

The Past Teaching the Present: Ancient Sanskrit Texts Discuss the Importance of Environmental and Species Conservation   Ancient Origins - September 15, 2015
One of the greatest challenges facing humanity in the 21st century is the destruction of the natural environment. Researchers have found that environmental change over the last 60 years is happening at a rate unseen in the past 10,000 years. Human-driven climate change, the loss of biosphere integrity, land system change, and the high amounts of biochemicals flowing into oceans due to fertilizer use are said to have reached an unsafe level. With these problems in mind, environmental conservation has become a hot topic in modern society. Nevertheless, this concept has been around for a much longer period of time, and can even be found in Sanskrit texts from ancient India.

'Archeologists of the air' isolate pristine aerosol particles in the Amazon   PhysOrg - September 16, 2010
Environmental engineers who might better be called "archeologists of the air" have, for the first time, isolated aerosol particles in near pristine pre-industrial conditions. Working in the remote Amazonian Basin north of Manaus, Brazil, the researchers measured particles emitted or formed within the rainforest ecosystem that are relatively free from the influence of anthropogenic, or human, activity. The findings could provide crucial clues to understanding cloud formation, determining the specific chemical differences between natural and polluted environments, and modeling how changes in the Amazon Basin might affect the regional and global atmosphere.

Klondike Holds Clues to Ancient Environment   Live Science - October 30, 2009
The Klondike region of the Canadian Arctic isn't often thought of as an oasis for life. Today, the area is best known for its vast frozen wilderness, its goldfields, and as the namesake of a popular chocolate-coated ice cream treat. However, new research shows that the Klondike goldfields of Canada's Yukon Territory hold key records of a past environment that was much different than the harsh climate experienced by today's explorers, ice truckers and miners. The Klondike is part of a wider geographic area dubbed "Beringia," which includes parts of Siberia, Alaska and the Canadian Yukon. The term Beringia was coined in the first part of the 1900s to explain the distribution of Arctic plants and coniferous forests of the boreal environment surrounding the Bering Strait.

What is a 100-Year Storm?   Live Science - September 22, 2009
The torrential rains that have inundated Atlanta, Ga., and its surrounding areas over the past few days have been called a 100-year storm event by state weather experts. Does that mean such a storm comes only once a century? Actually, no - the story is a little more complicated than that. Meteorologists, climatologists and hydrologists calculate 100-year events as a statistical tool to determine the likelihood of intense storms or floods. For example, meteorologists use the average year-to-year rainfall in a given area to figure out the chances of having a storm of potentially epic proportions, explained Pam Knox, Assistant State Climatologist of Georgia.