The world's species face an unprecedented crisis. The rate at which they are being lost is alarming, even when compared with the extinction episode of 70 million years ago when the dinosaurs disappeared. No-one knows exactly what the current extinction rate is, but recent calculations by leading scientists put it at between 1,000 and 10,000 times greater than it would naturally be. The rate of extinction also appears to be increasing. Species are threatened in every habitat on every continent, though the severity of threat varies from place to place. Evidence suggests that freshwater habitats, particularly rivers, and oceanic islands are very severely affected by species extinction. Tropical Asia and Australia appear to suffer particularly high extinction rates.

Some of the wealthier parts of the world have been successful in bringing about the recovery of certain species and greater efforts have been made to curb the loss of species over the past 20 years. Yet despite some isolated successes, conservation progress has generally been too little, too late, and the global situation continues to worsen.

There are many causes of the current extinction crisis, but all of them stem from unsustainable management of the planet by humans. Despite efforts to conserve key habitats for animal and plant species, widespread destruction of important habitats continues unchecked. Perhaps even more serious, the quality of habitats continues to deteriorate as a result of harmful activities such as overgrazing, selective logging, removal of dead wood, and burning.

A rapidly growing threat, and one which is very hard to control, is the spread of alien, invasive species. These species, both animals and plants, spread to areas and habitats where they do not naturally occur, displacing native species through predation, competition, disease and hybridisation. People move thousands of alien species around the globe, either deliberately or accidentally. Other species become established outside their natural range by taking advantage of new habitats modified by humans.

Over-harvesting of species, both animals and plants, that are valuable, either for economic or cultural reasons is another universal threat. Such harvests can be intentional (such as timber harvesting, the ivory trade or the pet trade) or unintentional (such as by-catch - the capture of non-target species in fisheries). Many species now appear to be suffering serious declines as a result of climate change, yet the full effects of the problem are little understood. The list of threats goes on - pollution, freak weather events, and disease can all have devastating effects. When species decline so that only very small populations survive, additional, biological factors begin to operate against them. These can include reduced genetic health of the population, and reduced reproductive success.

Presenting a full catalogue of the threats to species can be a depressing task but it should be noted that relatively few of these threats are intentional, or are specific to a particular species. Most relate to large-scale modifications of the Earth's surface by humans, and the loss of species is largely an unintended by-product of the way people have chosen to live. Behind the threats are powerful driving forces that push species to extinction at an increasing rate. For instance, the increasing economic wealth of much of the world is making demands on the natural environment that cannot be met, leading to habitat destruction, over-harvesting of animals and plants, pollution, and climate change. At the opposite end of the spectrum, in the poorer regions of the world, poverty is forcing people to adopt modes of subsistence living involving activities such as burning and over-grazing that are destroying critical habitats for species. The trend to increasing economic globalisation and the relaxation of trade controls lies behind the uncontrolled spread of invasive species.

There have been some successes in species conservation over the last 20 years. The decline of the black rhinoceros has been halted, and the species is slowly recovering. The unsustainable trade in certain parrot species has stopped. Several crocodile populations are now well managed and increasing through carefully regulated, sustainable harvesting programmes. In some places, species have been re-introduced to parts of their former range, and are increasing, such as the Arabian oryx in Jordan. However, these are only isolated examples and such successes are generally achieved through large investments that tackle immediate threats. There have been very few attempts to address the underlying driving forces of species loss.

For the species extinction crisis to be addressed effectively, far greater action is needed, aimed at both the immediate threats to species and the driving forces causing their decline. Addressing these forces will be particularly challenging, because it raises questions about the sustainability of human lifestyles. These issues will only be tackled if there is much greater support for lifestyle changes, and this involves the political will of governments. Although the world is slowly beginning to address sustainability issues, it is sobering to remember that vast levels of investment and action are needed simply to stop the rate of extinction increasing, let alone bring it under control.