Wildlife Numbers Drop by Half Since last four decades

Earth lost half its wildlife in the past four decades, according to the most comprehensive study on animal populations to date, a far larger decline than has been previously reported.

The latest analysis was done by scientists at the wildlife group WWF, the Zoological Society of London and other organizations. Based on an analysis of thousands of vertebrate species, it concludes that overall animal populations fell by 52% between 1970 and 2010.

The animal population decline was seen everywhere—in rivers, on land and in the seas—and is mainly the result of increased habitat destruction, hunting and fishing, the report said. Climate change is also believed to be a factor, though its consequences are harder to measure.

The previous WWF report analyzing animal populations was published in 2012 and it suggested a decline of 28%. The latest report has 15% more data than the previous one; it is more representative of tropical species; and it includes an improved methodology.

The fastest declines were seen in rivers and other freshwaters systems, where populations have fallen 76% since 1970. By comparison, terrestrial and marine populations each fell 39%.

While biodiversity continues to decline in both temperate and tropical parts of the world, the downward trend is greater in the tropics.

The most dramatic decline was in Latin America, where overall populations of mammals, birds, reptiles, amphibians and fish fell 83%. Asia-Pacific wasn't too far behind, though.

The new findings are calculated using the WWF's "Living Planet Index," a measure of biodiversity based on trends in 10,000 populations of about 3,000 animal species.

The WWF has been compiling its index since 1998. It tracks a large number of animal populations just as a stock market index tracks the value of a group of stocks. The data used in compiling the index are population size, density or a measure of abundance over a length of time.

In a separate section, the WWF report also tries to measure the state of humanity's ability to live in a sustainable way. With the planet's population expected to swell by another 2.4 billion people by 2050, the challenge of providing everyone with food, water and energy will be a difficult one.

The report analyzes sustainability by calculating a global "ecological footprint," which measures the area required to supply the ecological goods and services we use. It concludes that humanity currently needs the regenerative capacity of 1.5 Earths to supply these goods and services each year.

The study says: "This 'overshoot' is possible because—for now—we can cut trees faster than they mature, harvest more fish than the oceans can replenish, or emit more carbon into the atmosphere than the forests and oceans can absorb." Since the 1990s, we have reached that overshoot by the ninth month of each year, it adds.

"It's a very loud wake-up call," said Carter Roberts, president and chief executive officer of WWF US, in an interview. "As we lose natural capital, people lose the ability to feed themselves and to provide for their families—it increases instability exponentially. When that happens, it ceases to be a local problem and becomes a global one."