Earth is most likely experiencing its sixth mass extinction. The planet has been through at least five such catastrophes before, but this is the first one in human history — and the first one with human fingerprints.

A report by the World Wildlife Fund (WWF) offers sobering details about this decline, which has already cut the planet's vertebrate wildlife populations by an average of 60 percent in just 40 years. The Living Planet Report reveals the troubling extent of this and other environmental crises around the world, but it also sheds light on the ways we can still protect and rehabilitate what's left.

"Science is showing us the harsh reality our forests, oceans and rivers are enduring at our hands," says Marco Lambertini, director of WWF International, in a statement. "Inch by inch and species by species, shrinking wildlife numbers and wild places are an indicator of the tremendous impact and pressure we are exerting on the planet, undermining the very living fabric that sustains us all: nature and biodiversity."

The Living Planet Report is released by the WWF every two years. The full report spans 140 dense pages in a 15-megabyte PDF, and as WWF chief scientist Jon Hoekstra acknowledged in 2014, these reports "can seem very overwhelming and complex." Here are a few key takeaways:

The critically endangered Hainan gibbon lost about 80 percent of its total population over the past 50 years. It's now considered the rarest ape on Earth, with just 28 living in a single nature preserve. (Photo: Jessica Bryant/ZSL)

1. Wild Vertebrate Populations Are Declining

Earth's population of wild vertebrates — all mammals, birds, reptiles, amphibians and fish — experienced an overall decline of 60 percent from 1970 to 2014, the most recent year with available data. (By comparison, the 2016 and 2014 editions reported a 58 percent and 52 percent decline since 1970, respectively.)

2. Many Researchers Worked on the Report

More than 50 researchers from around the world contributed to the 2018 report, analyzing a total of 16,704 animal populations from 4,005 species.

3. Habitat Loss Is the Biggest Threat to Vertebrates

The No. 1 cause of the decline is habitat loss and degradation, which accounts for nearly half of all threats within each taxonomic group, except fish (28 percent). Common threats to wildlife habitat include "unsustainable agriculture, logging, transportation, residential or commercial development, energy production and mining," the report notes, adding that "fragmentation of rivers and streams and abstraction of water" are also prevalent causes in freshwater ecosystems.

Dead trees stand in a recently deforested section of the Amazon rainforest near Abunã, Brazil, in 2017. The past half century has seen about 20 percent of the Amazon vanish, according to the WWF. (Photo: Mario Tama/Getty Images)

4. Ecosystems Are Being Destroyed

This phenomenon is shrinking some of Earth's most iconic ecosystems — roughly 20 percent of the Amazon rainforest has disappeared in just 50 years, for example, while about half of all shallow-water corals have been lost in the last 30 years. Yet it also threatens many other, less famous habitats such as wetlands, which have lost 87 percent of their extent in the modern era, according to the report.

5. Overexploitation Is Another Serious Threat to Vertebrates

The No. 2 overall cause is overexploitation, which refers not only to the deliberate hunting, poaching and harvesting of wildlife, but also to the unintentional killing of non-target species, commonly known as bycatch. Overexploitation is a particularly big problem for fish, accounting for 55 percent of threats facing fish populations.

Aside from fish themselves, overfishing also threatens other marine animals like the vaquita, a porpoise that's nearly extinct due to entanglement in fishing nets used by totoaba poachers. (Photo: Paula Olson/NOAA)

6. Other Human Activities Also Pose Major Threats

Other top threats include invasive species, disease, pollution and climate change. The latter is most commonly reported as a threat for bird and fish populations, the report notes, accounting for 12 percent and 8 percent of threats, respectively.

7. Freshwater Habitats Have Been Especially Hit Hard

The fastest wildlife decline is in freshwater habitats, which lost 83 percent of their vertebrate populations between 1970 and 2014. The total number of freshwater vertebrates drops by about 4 percent each year.

The Shenandoah salamander is an endangered species that exists only in Virginia's Shenandoah National Park. About half of all salamander species on Earth are now considered threatened with extinction. (Photo: Brian Gratwicke [CC BY 2.0]/Flickr)

8. Tropical Regions Are Also Particularly Vulnerable

The planet's tropical regions are losing vertebrate species at an especially dramatic rate, with South and Central America suffering an 89 percent decline since 1970. That's the most pronounced decline of any "biogeographic realm," according to the report, followed by the Indo-Pacific (64 percent), Afrotropical (56 percent), Palearctic (31 percent) and Nearctic (23 percent).

9. Habitat Availability for Vertebrates Is Also Declining

On top of tracking population declines, the 2018 report also looks at additional indicators related to species distribution, extinction risk and biodiversity. The Species Habitat Index (SHI), for example, offers "an aggregate measure of the extent of suitable habitat available for each species." Overall trends in the SHI for mammals fell by 22 percent since 1970, with the steepest regional decrease reported in the Caribbean at 60 percent. Other regions with declines greater than 25 percent were Central America, Northeast Asia and North Africa.

The critically endangered araripe manakin exists only in a small area of Brazil, where it faces ongoing pressure from agriculture and other land development, according to BirdLife International. (Photo: Rick elis.simpson [CC BY-SA 3.0]/Wikimedia Commons)

10. Biodiversity Is Declining Too

The report also provides a Biodiversity Intactness Index (BII) that ranges from 100 to 0 percent, with 100 representing "an undisturbed or pristine natural environment with little to no human footprint." The most recent global estimates suggest the BII fell from 81.6 percent in 1970 to 78.6 percent in 2014.

11. Biodiversity Is Vital to Human Civilization

Biodiversity is not merely a luxury that's "nice to have," as the report puts it, but a linchpin of human civilization that gives us vital resources. Globally, these ecosystem services are worth an estimated $125 trillion per year. As one example, the report examines how much we rely on the planet's pollinators — which are responsible for $235 billion to $577 billion in crop production per year — and how their abundance, diversity and health are affected by climate change, intensive agriculture, invasive species and emerging diseases.

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"The statistics are scary, but all hope is not lost," says Ken Norris, science director for the Zoological Society of London, in a statement about the report. "We have an opportunity to design a new path forward that allows us to co-exist sustainably with the wildlife we depend upon. Our report sets out an ambitious agenda for change. We are going to need your help to achieve it."

For more information — including ideas about what can be done to save the wildlife we have left — take a look through the full Living Planet Report (pdf). And for a quicker overview, check out this new WWF video about the report: