Marine life is under threat from over-fishing and pollution

Humans have destroyed more that 30% of the natural world since 1970, says the World Wide Fund for Nature, and the situation is getting worse.

In a report the conservation agency reveals what it calls a Living Planet Index - a type of global health check showing the damage that has been done to the environment in just one generation. The WWF hopes the bleak picture will scare governments into taking action.

Ecosystems under threat

Fresh water eco-systems have declined the most

The report focuses on forest, freshwater and marine ecosystems. Most alarmingly it says the populations of freshwater animal and plant species have halved since 1970.

Natural forests have declined by more than 10% in the same period. The amount of forest lost every year is equivalent in size to the area covered by England and Wales.

Jonathon Loh: The results were surprising

The report's author, Jonathon Loh, says that the Living Planet Index will try to track the state of the global environment "like the Dow Jones Index tries to track the New York stock exchange."

The index will be updated annually and is available for all to see on the WWF website.

Prof Prance, Kew Botanical Gardens: The report gives a clear picture

For Mr Loh the most important discovery is that freshwater ecosystems have been so badly affected.

"You hear a lot about forest and marine environments being under attack - but the fact is that freshwater ecosystems have been hardest hit, although they've received the least attention," he said.

Species in decline

But does the report's grim findings mean that many species have become extinct all over the globe? According to the experts that is difficult to prove because a species has to disappear for 50 years before it can be declared extinct - but it is certain is that many species are in decline.

Mr Loh cites the example of the island of Mauritius where nearly 40% of the bird and animal species are threatened as a result of habitat loss and the introduction of invasive species, not native to the island.

Half of all the world's forests have disappeared, says the WWF

The exact causes of species decline differs from region to region. In Thailand the ancient coastline mangrove forests have been badly affected by pollution, tourist development and shrimp farming. Once the balance of nature is disturbed, the results can be disastrous. The dying mangrove forests are also home to some of the region's marine wildlife which in turn provides food for the local bird population.

Another area where species are in decline is in the Atlantic and Pacific oceans. Marine fish consumption has more than doubled since 1960 and this over-exploitation of fish stocks combined with pollution has badly affected marine life.

The developed world 'to blame'

The WWF mainly blames the decline of the natural world on the pressure exerted by the developed world. It says human consumption has doubled over the last 25 years and continues to accelerate.

Although the report is bleak, the WWF says some of the decline can be reversed if people in the developed world commit themselves to action on a personal level.

The agency recommends that everyone takes a look at their own consumption habits and adjust them, for example: by using less water and recycling packaging.

Influencing policy

But more importantly the WWF hopes the report will have a major impact on politicians around the world and influence conservation policy, encouraging more sustainable development and consumption patterns.

Professor Ghillean Prance, Director of the Royal Botanical Gardens at Kew, in London, says the report is "something definite" that can be used in conservation planning.