A global assessment of ecosystems across the planet shows that “exploitation of terrestrial systems”—in other words, human land use from road-building to industrial agriculture—has pushed biodiversity below “safe” levels. 

The study, published Thursday in the journal Science, finds that for 58 percent of the world’s land surface, which is home to roughly 71 percent of the global population, the level of biodiversity loss is “substantial enough to question the ability of ecosystems to support human societies.”

“Until and unless we can bring biodiversity back up, we’re playing ecological roulette.”
—Andy Purvis, Imperial College London

The researchers cite “land use and related pressures” as the cause of this decline, with grasslands, savannas, and shrublands most affected by biodiversity loss, followed closely by many of the world’s forests and woodlands.

“Biodiversity supports a number of functions within ecosystems, things like pollination, nutrient cycling, soil erosion control, maintenance of water quality,” lead author Tim Newbold of the United Nations Environment Programme and University College London told the Washington Post. “And there’s evidence that if you lose biodiversity, that these functions don’t happen as well as they would have done in the past.”

Newbold added in a press statement: “The greatest changes have happened in those places where most people live, which might affect physical and psychological wellbeing.”

As the Christian Science Monitor explains, the assessment “was based on a Biodiversity Intactness Index (BII), which measures changes in species abundances across the globe and places a safe limit of species decline at 90 percent of the total population that would exist in a pristine version of that habitat—one free of human activity. Once populations drop below that threshold, scientists fear there will be a tipping point at which one species goes extinct, causing a domino effect that leads to the collapse of the ecosystem.”

Indeed, co-author Andy Purvis, a professor at Imperial College London and research leader at the Natural History Museum, told the BBC: “Once we’re the wrong side of the boundary it doesn’t mean everything goes wrong immediately, but there is a markedly higher risk that things will go badly wrong.”