Man-made negative alteration of the ecosystem that has widespread or long lasting consequences. Usually involves mass-killing of animals and plant systems, and frequently can include mass-killing of human beings, or severe disruption of human life requiring mass migration.

Of course 'negative' is a relative term. Some might view for example the Three Gorges Dam as an environmental disaster, requiring the migration of 1 million people. Others might see it as beneficial to stop flooding. Some might see the destruction of most of the North American Forest as beneficial, as it cleared land for farming and other uses. In Ireland, the clearning of forest led to the formation of bogs, which some people like for their beauty, as well as their products such as peat moss. Others might see these deforestations as negative.

A more cynical example would be, for example, that Saddam Hussein felt it was beneficial to get rid of the Madan people by draining the Al-Hawizeh marsh because they had joined Bush I in the Gulf War. Another example is the depopulation of the American Bison. It was thought by General William Sherman and others to be a good way to get rid of the American Indians living in the Great Plains, and would make way for the exploding population of the United States of America to take over the area.

Some disasters can be averted before they have drastic consequences, as is the case with the hole in the Ozone layer caused by CFCs, which were subsequently subjected to a near-total ban by various world governments.

Examples of disasters include:

• Chernobyl accident
• Bhopal disaster
• Arsenic poisoning in Bangladesh
• Draining of the Al-Hawizeh marsh
• Saddam Hussein's oil spill and Kuwaiti oil fires
• Depopulation of the American Bison
• The hole in the Ozone layer
• Destruction of most of the Virgin Forest in places like North America
• EPA Superfund sites
• Soviet Aral Sea mismanagement