Dr. Nitish Priyadarshi.
Nobody knows how many species exist on Earth today. About 1.82 million species have been given a specific name, but this is very incomplete sample of what is out there. In 1982, Terry Erwin of the Smithsonian Institute (Washington, DC, USA) publishes a report in which he proposed that estimates of biodiversity on Earth are seriously underestimated. He suggested that there might be 30 million species of insects alone. This conclusion was based largely on his finding that, in the tropical rainforest, insect species were often specific to individual trees. If any given tree in a tropical rainforest houses a number of unique insect species, it follows that there must be many millions more insect species than were previously believed. Estimates of the total number of species living today commonly range from 5 to 50 million, with some estimates as high as 100 millions.
The rapid disappearance of species was ranked as one of the planet's gravest environmental worries, surpassing pollution, global warming and the thinning of the ozone layer, according to the survey of 400 scientists commissioned by New York's American Museum of Natural History.
How many plants and animals will become extinct this year? This is a difficult question to answer. The ‘Red List’ of the International Union for Conservation of Nature and Natural Resources (IUCN, also known as the World Conservation Union), compiled in 2000, states that a total of 11,046 species of plants and animals are threatened with extinction in the near future, in almost all cases as a result of human induced activities such as, global warming, climate change, pollution etc. Of known species, this includes 24 per cent of mammals, 12 per cent of birds, 25 per cent of reptiles, 20 percent of amphibians and 30 per cent of fishes. BirdLife International lists 1,186 birds as being threatened world wide, up by 75 since 1994, with 99 per cent of these threatened as a result of human activity. A total of 182 of these bird species are described as critical, which means that they have only an estimated 50 per cent chance of surviving either the next 10 years or 3 generations, whichever is shorter. Over the last 600 years, 128 bird species have become extinct, most of them (103) since 1800. Since only a small proportion of reptiles, amphibians and fishes have been assessed, the percentage of threatened species could be much higher.
Presently environmentalists are concerned about the imbalances caused by human activity and industrial growth in the ecosystem, as it is slowly inundating the forest cover, thereby reducing considerably the area of natural habitat of animal and plant life. Carbon dioxide is increasing, earth is warming, climate is changing affecting the life on the earth.
Since life began on Earth, several major mass extinctions have significantly exceeded the background extinction rate. The most recent, Cretaceous–Tertiary extinction event, which occurred approximately 65.5 million years ago (Ma), was a large-scale mass extinction of animal and plant species in a geologically short period of time. In the past 540 million years there have been five major events when over 50% of animal species died. There probably were mass extinctions in the Archean and Proterozoic Eons, but before the Phanerozoic there were no animals with hard body parts to leave a significant fossil record.
Human beings are currently causing the greatest mass extinction of species since the extinction of the dinosaurs 65 million years ago. If present trends continue one half of all species of life on earth will be extinct in less than 100 years, as a result of habitat destruction, pollution, invasive species, and climate change.
The U.N. warns several eco-systems including the Amazon rainforest, freshwater lakes and rivers and coral reefs are approaching a "tipping point" which, if reached, may see them never recover. Vertebrate species fell by nearly one third between 1970 and 2006, natural habitats are in decline, genetic diversity of crops is falling and sixty breeds of livestock have become extinct since 2000.
A comprehensive survey of mammals included in the annual report by the International Union for Conservation of Nature (IUCN), which covers more than 44,000 animal and plant species, shows that a quarter of the planet's 5,487 known mammals are clearly at risk of disappearing forever.
But the actual situation may be even grimmer because researchers have been unable to classify the threat level for another 836 mammals due to lack of data.