These sobering figures were revealed at the launch of the tenth Living Planet Report this week.
Produced by the World Wide Fund for Nature (WWF), the Zoological Society of London (ZSL) and the Global Footprint Network, the biennial Report is highly regarded by environmental experts as an authoritative "report card" on the health of the planet and the impact of human activity.
Wildlife numbers halved
The most alarming statistic from the 2014 Report is that, since 1970, wildlife vertebrate populations - mammals, birds, reptiles, amphibians and fish - have declined by 52%.
Some species and regions have been even harder hit: 76% of freshwater wildlife has disappeared in the past 40 years, while 63% of animals in tropical regions are gone. Central and South America had the worst regional decline, of 83%.
Read: Almost half of Africa's lions facing extinction
The shocking drop-off in numbers was revealed through new research conducted by WWF and ZSL. An analysis was made of 10 000 animal populations, which included over 3 000 different species. This data was then used to create a “Living Planet Index”, which serves as an indicator for how all 45 000 vertebrate species in the world are faring.
Dramatic biodiversity losses such as these act as a barometer of our impact on the planet. The greatest threats to biodiversity are habitat loss and degradation, fishing and hunting, and climate change.
"The absence of birds in our skies and other wildlife in our forests and oceans sends a very clear signal that we are not living sustainably," says Marco Lambertini, director general of WWF International.
Our unsustainable resource use is threatening iconic wildlife like the
African lion. Lion population numbers have halved since the 1970s.
Humanity's footprint 50% bigger than Earth
A second index in the Report calculates humanity’s “ecological footprint” - a measure of how rapidly we are consuming natural resources.
Globally, demand on the planet is 50% greater than nature is able to renew, the Report finds. Glimmers of hope
Put another way, it would take 1.5 Earths to produce enough food, water and energy to support us at our current rates of consumption.
With world population expected to grow from 7.2 billion to over 9.5 billion by 2050, even 1.5 planets are unlikely to be enough, however.
Read: World population likely to soar this century
Sustaining ourselves means we have overshot Earth's carrying capacity. Says Lambertini:
"That means we are cutting trees faster than they can regrow, catching fish faster than they can reproduce, and emitting more CO2 than forests and oceans can absorb."
The consequence is diminished resource stocks and waste accumulating faster than it can be absorbed or recycled.
Read: Fat planet: how overeating harms the environment
WWF South Africa's CEO, Dr Morne du Plessis, illustrates the crisis our appetite for resources has put us in as follows:
"It's as if we're in a car driving at high speed, with a hairpin bend just up ahead," said . "We need to slow down to 20km/hr, but we're still going at 160km/hr."
South Africa's own footprint is around the average for nations, at around 2.3 global hectares (23 000 m2) per person. This is far above the maximum the planet can currently carry - 1.7 hectares (17 000 m2) per person.
SA's footprint is particularly high for a low- to middle-income country, because of our energy sector's heavy reliance on highly polluting coal.
Watch: WWF director general highlights key points of the Living Planet Report:
Although the Report's revelations are alarming and require urgent redress, the WWF points out that solutions are possible, and that there are a number of current successful projects that prove it can be done
For example, the Report shows that Cape Town – the global Earth Hour Capital 2014 – is working to reduce energy use by installing household solar water heaters and retrofitting streetlights with energy-efficient technology.
Du Plessis also cites South Africa's new Knersvlakte reserve - opened last week - as "an example of the importance of small-scale community-based conservation in preserving our natural capital."
"We need to produce better, and projects like the Biodiversity and Wine Initiative, a pioneering partnership between the Western Cape industry and the conservation sector to protect fynbos in winelands, shows this can be done.
"We need to consume better - here the South African Sustainable Seafood Initiative's (SASSI) consumer guide to sustainable seafood choices is another effective example."
Further heartening, say Du Plessis and Lambertini, is the marked global rise in awareness of environmental issues, and the resolve by civil society to mobilise and make positive change, as evidenced by last week's 400 000-strong march against climate change at the United Nation's climate summit in New York.
What are your thoughts about the Living Planet Report findings? Use #LPR2014 to tweet your reactions or comment on our Facebook page.
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Image of lions: Shutterstock
Olivia Rose-Innes is Health24’s EnviroHealth Editor. Read more of her columns and articles or post a question to her expert forum.