For the purpose of this article an environmental disaster is defined as a specific event caused by human activity that results in a seriously negative effect on the environment. Sometimes a natural disaster can become an environmental disaster, but that is a topic to be discussed elsewhere.

In most cases environmental disasters are caused by human error, accident, lack of foresight, corner cutting during industrial processes, greed, or by simple incompetence. In other words without some kind of human intervention they would never have happened. They are also often characterised by firm authoritative denials that anything serious has even happened.

Lack of foresight is a common cause of an environmental disaster. In agriculture a classic example of is the increasing salinity of soils in hot climates. With the need to produce more food, a warm climate seems ideal for European-style agriculture, once the existing vegetation has been cleared. The one proviso is that there must be plenty of water. Irrigation projects and deep wells are usually the answer, but as has been found in Australia, if this is not properly managed, salination can result and the land becomes effectively useless.

A further example of a catastrophic and misguided interference with nature resulted in the dust bowls that hit North America in the 1930s. The fertile soil seemed ideal for intensive agriculture, but a combination of deep ploughing and a lack of crop rotation weakened the soil structure. Following years of drought, high winds simply removed all the topsoil and millions of acres of once fertile farmland became a virtual desert.

Another unforeseen agricultural disaster was Moa Zedong's 1958 decree to eliminate sparrows. It was considered that because sparrows ate grain seeds they were robbing the people of the fruits of their labour. The campaign was very successful that it cleared the way for swarms of locusts to descend on the farms. Crops were decimated, leading to a famine that resulted in the deaths of 38 million people.

Introducing alien species can be just as disastrous as eliminating native ones. This has been the case in Australia when in 1859 12 imported English wild rabbits were released so that a local settler could go hunting. In the course of time they multiplied and it is estimated that even after serious efforts to control them, the Australian rabbit populations is still between 200 and 300 million.

As well as being responsible for the loss of vast acreages of agricultural crops and grazing land, rabbits are suspected of being the most significant known factor in species loss in Australia, killing young trees by eating the bark at the base of the trunk. They are also responsible for serious erosion as they eat native plants, leaving the topsoil exposed.

It is very easy to upset the fragile balance of nature. In June 1918 a steamship ran aground on a Pacific Island and while it was stranded, Black Rats escaped and got ashore. Here they thrived, causing the extinction of several of the island's endemic birds and other fauna. They also raided the crops of the islanders, particularly the seeds of the Kentia Palm, which was the islanders' only export commodity.

In an effort to control the rats, Masked Owls were introduced but this simply compounded the environmental disaster. By introducing yet another predator to the ecosystem, the result was that many of the remaining sea birds were simply wiped out as breeding species.

Industrial pollution has been the cause of so many environmental disasters that it is impossible to list them all. One of the most serious was the Bhopal disaster of December 1984 when a leak of methyl isocyanate resulted in at least 22,000 deaths plus various genetic diseases that will continue for generations. The chief causes of this disaster were negligence, corruption and the complete disregard of safety standards.

Videos: The Bhopal Documentary from National Geographic.

A number of environmental disasters have also been associated with the oil production industry with the Deepwater Horizon disaster of April 2010 being the most recent one that comes to mind. According to White House energy adviser Carol Browner the spill was the ''worst environmental disaster the US has faced''.

In this case following a sudden explosion on a drilling rig in the Gulf of Mexico, the safety valve that was designed to prevent an oil spill spectacularly failed. It was months before the leakage was sealed, during which time millions of gallons of oil poured into the sea.

The resulting pollution was not just from the oil, but from the chemicals used to disperse it. Whole ecosystems were destroyed along with the livelihoods of countless people. Many endangered species are not expected to recover.

In West Africa the Niger Delta covers 20,000 km² within wetlands of 70,000 km², formed primarily by sediment deposition. It is home to some 20 million people from 40 different ethnic groups. Its floodplain makes up 7.5% of Nigeria's total land mass and is the third-largest drainage basin in Africa.

Its ecosystem contains one of the highest concentrations of biodiversity on the planet. In addition to supporting a vast range of flora and fauna, there is arable terrain that can sustain a wide variety of crops, tropical forests and more species of freshwater fish than any other ecosystem in West Africa.

Unfortunately for the Niger Delta, oil was discovered in the region. Since drilling began in 1976 there has been a complete lack of concern by the Nigerian Government or the oil operators to exert any control of the environmental problems associated with the industry.

The Nigerian National Petroleum Corporation admits that every year as a result of around 300 individual spills, nearly 2,300 cubic metres of petroleum are jettisoned into the environment. However, this does not take account of so-called ''minor'' spills and one estimate put the total spillage between 1960 and 1997 as upwards of 100 million barrels (16 million cubic metres).

A major reason for these spills is simply the result of poor maintenance. Pipelines are old and corroded and although they have an estimated lifespan of about 15 years, many have been in use for about 25. Leaking pipes and the use of old and corroded tankers account for 50% of all spills.

Understandably there has been a major impact on the ecosystem. Enormous tracts of mangrove forest have been destroyed along with most of the flora and fauna that were once found there.

The dumping of waste is obviously a serious issue and international regulations put strict controls on this. Unfortunately there will always be unscrupulous people who will try to get around the regulations.

A classic example occurred in 2006 when a Panama-registered ship offloaded 500 tonnes of toxic waste at the Ivory Coast port of Abidjan. The company concerned apparently wanted to avoid paying the 1,000 euros per cubic metre disposal charge it would have to pay in Holland.

The waste, that was dumped at 12 sites in and around the city was later discovered to contain a mixture of fuel, caustic soda and hydrogen sulphide. This lethal cocktail gave off toxic gas and caused burns to lungs and skin, in addition to severe headaches and vomiting and is said to have caused 17 deaths and made dozens seriously ill.

The company involved originally denied all responsibility, claiming that the waste was simply dirty water. It was only after some investigative journalism by the BBC that the full facts eventually came to light.

Nuclear accidents can have serious environmental effects. Prior to 2011 the 1986 Chernobyl disaster would probably have been regarded as the most serious after an enormous explosion sent radioactive ash into the atmosphere covering most of Northern Europe, along with Belarus, Ukraine and Russia. 350,000 people had to be resettled.

Then in 2011 came the Fukushima 1 accident in Japan when an earthquake followed by a tsunami hit the nuclear plant. The earthquake knocked out the public electricity supply that powered the pumping of water to cool the reactors. Shortly after the earthquake a tsunami destroyed the emergency back-up generators that were due to start up when the public electricity supply failed. It was then realised that the designers had failed to take this possibility into account.

As a result a catastrophic situation developed and 14,000 people had to be evacuated from the immediate area. After several weeks a number of brave workers, struggling in appalling conditions, managed to bring the situation under control, but as with so many environmental disasters, once again official information was misleading, sketchy, or simply non-existent.

An environmental disaster is usually caused by some form human action, or some form of human negligence. A classic example is with climate change. Vast amounts of greenhouse gas are currently being released into the Earth's atmosphere, potentially doing untold harm to our environment by speeding up global warming. At the same time people are completely ignoring the warning signs and shutting their minds to the consequences that lie ahead.

We don't know what these consequences will be, but they are not likely to be pleasant. The world seems to be on course for what is likely to be the worst environmental disaster of all time. There is still time to slow the process down, but it will require swift and worldwide action.