The world's wildlife has declined by nearly a third over the past 40 years, a new estimate of the health of the planet suggests. In some parts the figure is much higher – in the tropics, losses are estimated at more than 50 per cent, while in tropical freshwater ecosystems specifically, average losses may be as high as 70 per cent, according to the 2012 edition of the Living Planet Report, produced by the WWF.
Typical high declines include the wild tiger, which has suffered a 70 per cent decline in the size of populations, and run right up to the extreme case of the baiji, the freshwater dolphin from China's Yangtze river, which appears to have become extinct in recent years.
However, in northern areas such as Europe and North America, wildlife populations are doing much better, reflecting the amount of conservation that wealthy societies are able to afford.
The Living Planet Report is published every two years and is based on the Living Planet Index, an aggregated measure of the health of more than 9,000 populations of more than 2,600 species, collated by the Zoological Society of London.
The wildlife index is accompanied by an appraisal, the Ecological Footprint, which measures the impact of humanity on the earth's natural resources. In the latest report, the Ecological Footprint is shown as exceeding the earth's capacity to replace what humans are taking by more than 50 per cent – in other words, we are using one-and-a-half times the resources naturally produced each year and the wastes that can be absorbed (including the carbon dioxide emissions which are causing climate change).
The contrast of the two measures – the wildlife index right down and the human exploitation index right up, reflecting expanding population levels – means that we are using up the earth's natural capital, the report says.
"We're now in the danger zone, exceeding the planetary boundaries for natural capital," said David Nussbaum, chief executive of WWF-UK. "If we continue to use up our planet's resources faster than it can replace them, soon we'll have exploited every available corner of the earth.
"Thankfully it's not too late to reverse this trend, but we need to address this with the same kind of urgency and
determination we tackled the systemic financial crisis globally."
Jonathan Baillie, conservation programme director with the Zoological Society of London, said: "This report is like a planetary check-up and the results indicate we have a very sick planet. Ignoring this diagnosis will have major implications for humanity.
"We can restore the planet's health, but only through addressing population growth and over-consumption of resources."
The detail of the Living Planet Index shows that since 1970, the global tropical index has declined by 60 per cent, but the global temperate index – the wildlife portrait of the temperate zones, including much of Europe and North America – increased by 31 per cent. However, says the report, "this disguises huge historical losses prior to 1970".
The report has been released early to set the agenda for "Rio Plus 20" – the UN conference on sustainable development to be held in Rio de Janeiro next month.
The June meeting marks the 20th anniversary of the Earth Summit, the major gathering of more than 100 world leaders held in the Brazilian city in 1992, which saw the signing of the UN conventions on biodiversity and climate change.
The anniversary summit will try to set out future guidelines and goals for sustainable development – essentially, economic growth without trashing the environment.
"Since the original Earth Summit, we've taken some steps forward, but the pace is glacial," Mr Nussbaumsaid. "So Rio Plus 20 needs to elevate the urgency of action on the scale needed: now is our chance to reflect whether the future we're creating for our planet is the legacy we want to leave for future generations."