The commons is a concept that has been used in many societies for centuries, usually when referring to land such as the village square or fields used for grazing livestock, that was not privately owned but belonged to the community as a whole. Global commons is a more recent concept, most often used in economics and politics, and usually refers to various natural resources and geographical areas, commonly including the deep sea bed, outer space, the oceans, the continent of Antarctica, and sometimes the entire Earth. These global commons are internationally shared resources and spaces that are not under the ownership or control of any state or person. Often, global commons are also defined as being necessary for human survival. The concept of global commons is most commonly used when debating environmental issues such as global warming and overfishing, and in discussions about how to implement and enforce laws to protect and manage these shared resources.
There is no universally accepted definition of what constitutes global commons. However, in an international report from 1980, backed by several international organizations, global commons are said to include the oceans, the atmosphere, "parts of the earth's surface beyond national jurisdictions," and Antarctica. The concept is sometimes broadened to include social, intellectual and cultural resources such as traditions, languages, and scientific knowledge.
James Quilligan, an international economist, has defined three types of global commons. These are: the biosphere, which includes areas and resources such as land, ecosystems, and living creatures; the physiosphere, which includes water, climate, and atmosphere; and the noosphere, which includes culture, art, the Internet, and religions. A related concept is public commons, a more general term that usually refers to places or natural features, such as parks, rivers, and mountains that can be enjoyed for free by anyone.
The problems with managing shared resources such as global commons are sometimes called "the tragedy of the commons," a concept often explored in environmental economics. One problem often mentioned is that while the benefits of a shared resource can be enjoyed fully by each individual, the effects of any damage an individual does to the resource is shared and does not specifically hurt only the person doing the damage. This means that rational short-term decisions by individuals, or nations, can lead to the destruction or depletion of a globally shared resource in the long term. Overfishing and air pollution, and the difficulties in establishing international rules to deal with these issues, are commonly stated as examples of the tragedy of the commons.