The world is heading for an "ecological credit crunch" far worse than the current financial crisis because humans are over-using the natural resources of the planet, an international study warns today.

The Living Planet report calculates that humans are using 30% more resources than the Earth can replenish each year, which is leading to deforestation, degraded soils, polluted air and water, and dramatic declines in numbers of fish and other species. As a result, we are running up an ecological debt of $4tr (£2.5tr) to $4.5tr every year - double the estimated losses made by the world's financial institutions as a result of the credit crisis - say the report's authors, led by the conservation group WWF, formerly the World Wildlife Fund. The figure is based on a UN report which calculated the economic value of services provided by ecosystems destroyed annually, such as diminished rainfall for crops or reduced flood protection.

The problem is also getting worse as populations and consumption keep growing faster than technology finds new ways of expanding what can be produced from the natural world. This had led the report to predict that by 2030, if nothing changes, mankind would need two planets to sustain its lifestyle. "The recent downturn in the global economy is a stark reminder of the consequences of living beyond our means," says James Leape, WWF International's director general. "But the possibility of financial recession pales in comparison to the looming ecological credit crunch."

The report continues: "We have only one planet. Its capacity to support a thriving diversity of species, humans included, is large but fundamentally limited. When human demand on this capacity exceeds what is available - when we surpass ecological limits - we erode the health of the Earth's living systems. Ultimately this loss threatens human well-being." Speaking yesterday in London, the report's authors also called for politicians to mount a huge international response in line with the multibillion-dollar rescue plan for the economy. "They now need to turn their collective action to a far more pressing concern and that's the survival of all life on planet Earth," said Chief Emeka Anyaoku, the president of WWF International.

Sir David King, the British government's former chief scientific adviser, said: "We all need to agree that there's a crisis of understanding, that we're removing the planet's biodiverse resources at a rate which is as fast if not faster than the world's last great extinction."

At the heart of the Living Planet report is an index of the health of the world's natural systems, produced by the Zoological Society of London and based on 5,000 populations of more than 1,600 species, and on an "ecological footprint" of human demands for goods and services.

For the first time the report also contains detailed information on the "water footprint" of every country, and claims 50 countries are already experiencing "moderate to severe water stress on a year-round basis". It also shows that 27 countries are "importing" more than half the water they consume - in the form of water used to produce goods from wheat to cotton - including the UK, Switzerland, Austria, Norway and the Netherlands.

Based on figures from 2005, the index indicates global biodiversity has declined by nearly a third since 1970. Breakdowns of the overall figure show the tropical species index fell by half and the temperate index remained stable but at historically low levels. Divided up another way, indices for terrestrial, freshwater and marine species, and for tropical forests, drylands and grasslands all showed significant declines. Of the main geographic regions, only the Nearctic zone around the Arctic sea and covering much of North America showed no overall change.

Over the same period the ecological footprint of the human population has nearly doubled, says the report.

At that rate humans would need two planets to provide for their wants in the 2030s, two decades earlier than the previous Living Planet report forecast just two years ago. This figure is "conservative" as it does not include the risk of a sudden shock or "feedback loop" such as an acceleration of climate change, says the report. But it warns: "The longer that overshoot persists, the greater the pressure on ecological services, increasing the risk of ecosystem collapse, with potentially permanent losses of productivity."

In the 1960s most countries lived within their ecological resources. But the latest figures show that today three-quarters of the world's population live in countries which consume more than they can replenish.

Addressing concerns that national boundaries are an artificial way of dividing up the world's resources, Leape says: "It's another way of reminding ourselves we're living beyond our means."

The US and China account for more than two-fifths of the planet's ecological footprint, with 21% each.

A person's footprint ranges vastly across the globe, from eight or more "global hectares" (20 acres or more) for the biggest consumers in the United Arab Emirates, the US, Kuwait and Denmark, to half a hectare in the Democratic Republic of Congo, Haiti, Afghanistan and Malawi. The global average consumption was 2.7 hectares a person, compared with a notional sustainable capacity of 2.1 hectares.

The UK, with an average footprint of about 5.5 hectares, ranks 15th in the world, just below Uruguay and the Czech Republic, and ahead of Finland and Belgium.