Many studies look ahead to the future when assessing humanity's impact on the environment, but according to the World Wildlife Fund, plenty of damage has already been inflicted. As Newsweek reports, 60 percent, on average, of the world's mammal, bird, fish, reptile, and amphibian populations have been wiped out since 1970.

Every two years, the WWF releases its Living Planet Report [PDF] examining the state of life on Earth. After analyzing 16,704 populations of 4005 vertebrate species, the organization reports that there's been widespread decline across the world's ecosystems in recent decades. Freshwater wildlife was hit the hardest, with populations plummeting by 83 percent between 1970 and 2014. In terms of regions, the "neotropical realm," comprising Central and South America and the Caribbean, has seen some of the biggest changes. According to the study, wildlife there has shrunk by 89 percent.

The WWF points to human activity as the chief cause of the massive loss of biodiversity in the past half-century. Some of the biggest threats include deforestation, over-fishing, pollution, and climate change. If current trends continue, it could spell disaster, not just for the world's ecosystems, but for the human populations that depend on them for their livelihoods.

Despite the dismal results of the study, the WWF isn't entirely pessimistic. The chief executive for their UK branch, Tanya Steele, said in a statement, "We are the first generation to know we are destroying our planet and the last one that can do anything about it." The report emphasized that the year 2020 will present critical opportunities for global change, with world leaders reviewing the progress of pacts like the Sustainable Development Goals, the Paris Climate Agreement, and the Convention on Biological Diversity.

[h/t Newsweek]