A sweeping report assessing the state of the natural world found that humans are having an "unprecedented" and devastating effect on global biodiversity, with about 1 million animal and plant species now threatened with extinction.
A summary of the report's findings was released Monday by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, which was established in 2012 by the United Nations Environment Programme and includes representatives from 132 countries.
Robert Watson, the panel's chair and a professor of environmental sciences at the University of East Anglia in the U.K., said evidence collected over the past five decades from roughly 15,000 scientific and government studies paints "an ominous picture."
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"The health of ecosystems on which we and all other species depend is deteriorating more rapidly than ever," he said in a statement. "We are eroding the very foundations of our economies, livelihoods, food security, health and quality of life worldwide."
The report, which did not list individual species, found that 25 percent of mammals, more than 40 percent of amphibian species, nearly 33 percent of sharks and 25 percent of plant groups are threatened with extinction. Based on these proportions, the researchers estimated that approximately 1 million animal and plant species could die out, many "within decades."
Since the 16th century, humans have driven at least 680 vertebrate species to extinction, including the Pinta Island tortoise. The last known animal of this subspecies, a giant tortoise nicknamed Lonesome George, died at the Galapagos National Park in Ecuador in 2012. A subspecies of the Javan rhino went extinct in 2011, and the western black rhino and northern white rhino are extinct in the wild, according to the World Wildlife Fund.
"The essential, interconnected web of life on Earth is getting smaller and increasingly frayed," Josef Settele, the report's co-chair, said in a statement.
Extinctions have occurred throughout the planet's history, but the report found that human act
ions threaten more species now than ever before, with the global rate of species extinction over the past 50 years already "at least tens to hundreds of times higher than it has averaged over the past 10 million years."
This quickening pace should be cause for alarm, according to David Wagner, a professor of ecology and evolutionary biology at the University of Connecticut, who was not involved with the report.
"It's happening faster than organisms can respond evolutionarily," Wagner said. "That means new species generation won't be able to keep pace with the loss of species."
This could have serious consequences for the stability of ecosystems around the world, which in turn could directly affect human health, experts say. The interactions between animals, plants, humans and the environment make up a complex web. Disruptions to any part of this biological architecture can have significant, cascading effects.
For instance, humans need food to survive. More than three-quarters of the world's food crops rely, at least in part, on the activities of bees, wasps, butterflies and other pollinators, according to the Food and Agriculture Organization of the United Nations. The new U.N. report found that 10 percent of insect species are under threat.
"When you lose a species, think of it like a fabric, and you're taking and plucking one of the strings," said Brett Scheffers, a conservation ecologist at the University of Florida in Gainesville, who was not involved with the report. "Over time, the fabric gets looser and less stable. These are the types of changes we're observing where entire ecosystems collapse."
Jessica Ware, an evolutionary biologist at Rutgers University in Newark, New Jersey, said the situation for insects could be even more dire than recent research shows because scientists don't have a good grasp of the number of insect species.
"There are more insects than anything else on Earth, and they are the most diverse group of organisms, but it's estimated that upwards of 10 million more species haven't even been described yet," she said. "If you don't know the number of species you have, it's hard to know how many you're losing."
The primary threats to biodiversity identified in the report include changes in land use — such as expanding urban areas and devoting more land to agriculture or livestock — as well as pollution, poaching, overfishing and climate change.
In many cases, these changes are working in tandem to destroy animal and insect habitats or force species to migrate to other regions, where they may be ill-suited to survive.
"There's no one answer for the cause," Wagner said. "It's death by a thousand cuts."
The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services convened in Paris last week to finalize details of the assessment — the first to be released by the group since 2005.
The report, which is designed to guide policymakers on conservation and sustainability decisions, states that "urgent and concerted efforts fostering transformative change" are necessary to halt or reverse the alarming declines in biodiversity.
Chief among the proposed solutions is reducing greenhouse gas emissions, which is the main driver of human-caused climate change. A report published in December 2018 by the Global Carbon Project, an international consortium of researchers that studies emissions trends, showed that after a brief period of stability from 2014 to 2016, global greenhouse gas emissions rose more than 2 percent in 2018.
Watson, the panel's chair, said that although climate change issues tend to garner more attention, it's also necessary for governments to focus on preserving biodiversity.
"Loss of biodiversity is just as important as climate change for the future of mankind," he told reporters Sunday in a news briefing. "The two are highly coupled. You can't deal with climate change without dealing with biodiversity."
The assessment highlighted the need to adopt sustainable agriculture, forestry and land-use practices. And the panel advocated expanding protected areas to shield species and to allow ecosystems to recover.
Despite the dire prognosis, John Wiens, a professor of ecology and evolutionary biology at the University of Arizona, said most scientists agree that the planet has not passed the point of no return.
"It's not too late — there's a 10- or 20-year window in which we can still do something," Wiens said. "In the end, all it takes is will. If we decide we want to solve it, we can solve it."