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Sixth mass extinction ‘tsunami’ coming, but preventable

  • Biologist Thomas Lovejoy writes in the Proceedings of the National Academy of Sciences that we can stop the current spate of biodiversity and species loss that the Earth is experiencing.
  • Pointing to a recent study showing that many animals are declining in numbers in addition to those facing the imminent risk of extinction, Lovejoy argues that we need to address all of the impacts that humans have on ecosystems.
  • He calls for the restoration of degraded forests and wetlands — activities in which everyone can participate — to facilitate the movement of wildlife between habitats and bring back the services that ecosystems provide.

Planet Earth is barreling through its sixth mass extinction right now, and there’s little doubt among scientists that we humans are responsible. Despite the challenges we face, the encouraging twist this time is that we can do something about it, says biologist Thomas Lovejoy.

“In contrast to any of the other mass extinctions, this is one where one species is responsible and is completely capable of being aware of it and actually stopping it,” he said in an interview. A professor at George Mason University in Fairfax, Virginia, and the “godfather of biological diversity,” Lovejoy recently crafted an essay for the journal Proceedings of the National Academy of Sciences (PNAS) in which he highlighted the importance of taking into account all of the changes we’ve foisted on the planet to address this unprecedented loss of species.

A tree frog (Hyla sp.) in the Peruvian Amazon. Photo by Rhett A. Butler / Mongabay

“We’re hardwired by evolution to react to immediate things,” Lovejoy said, “but we also have a fair amount of mental capability that allows us to actually look ahead and project what’s going on.”

What is going on, according to recent research that also appeared in PNAS by another team of scientists, is that the numbers of one-third of the 27,600 vertebrate species that the team looked at are falling, including many that we don’t consider close to being wiped out. To be sure, Earth is midstream in an extinction blitz, in which we’ve been losing about two species a year for the past century — up to 100 times faster than “normal” extinction rates. But the authors of the study, published on July 10, write that outright loss of these animals has been masking the downward slide of a great many more.

“What they highlighted so well is that extinction is not just an event,” Lovejoy said. “It’s a process.”

So while it is critical to tackle immediate threats such as poaching and habitat loss by protecting the areas where threatened animals live, we also must find ways to confront the furtive knock-on effects “that could otherwise undercut locally focused efforts,” Lovejoy writes.

Numbers of the African savanna elephant (Loxodonta africana) have declined by 30 percent in the past seven years. Photo by John C. Cannon

As an example, he points to the dynamics of water in the Amazon rainforest, which Lovejoy knows well after more than five decades of fieldwork there. More than 50 percent of the world’s largest rainforest is currently protected in some way, but he writes that even that “impressive” figure may not be enough to stem the loss of species.

As humans cut down other parts of forest, often for the farms and ranches that supply our food, it could disrupt the cycle in which rain falls in the forest and then flows back into the atmosphere through evaporation and the transpiration of resident plants. The protected habitat that’s home to many of the Amazon’s animals might still stand. But at some point — Lovejoy figures when we’ve lost more than 20 percent of the rainforest to deforestation — that cycle could rupture, leading to a cascade of degradation, even to areas of safeguarded forest that are part of the larger system.

“If we’re going to take the extinction threat seriously, we have to look at all these vectors and recognize that, in the end, it’s not just about going off and saving something before the last one is snuffed out,” Lovejoy said. “It’s about addressing these drivers.”

The authors of the PNAS study referred to the global loss of biodiversity as an “annihilation.” That’s not a term lead author Gerardo Ceballos and his colleagues toss around lightly.

“As scientists, we have to be very careful not to be alarmist, saying things that are not supported by science,” said Ceballos, a biologist at the National Autonomous University of Mexico. But they decided that the results of their analysis warranted such strong language.

The leopard (Panthera pardus), pictured here in Tanzania, is a highly adaptable animal. Nevertheless, it’s less prevalent than it used to be and is listed as Vulnerable by the IUCN. Photo by John C. Cannon

“It would be unethical not to say how bad things are according to our data,” he added. They also did a deep dive into previous research on 177 better-known vertebrates. The habitats of every single one had been cut by a minimum of 30 percent since the beginning of the 20th century. Forty percent of the animals experienced 80 percent or more habitat loss in that same time period.

“I wish I was wrong” about their results, Ceballos said.

In Lovejoy’s essay for PNAS, he said that the scale of such global problems demands equally ambitious solutions, such as the Half Earth Project “in which human ambition is embedded in nature.”

Although such efforts might appear “impossibly dreamy,” Lovejoy said there are manageable ways to start.

Climate change is another process that could undermine functioning ecosystems. However, if we began by restoring forests, wetlands, and other habitats that we’ve had a hand in degrading, Lovejoy thinks that we could sidestep as much as a 0.5-degree-Celsius (0.9-degree-Fahrenheit) increase in the global temperature because of the additional carbon these areas could then pull out of the atmosphere. The 2015 Paris agreement on climate change aims to keep the increase below 2 degrees C above what the average temperature was before the Industrial Revolution.

“If we [restore these spots], we get a whole bunch of additional benefits,” Lovejoy said. “The ecosystems will be functioning properly again and providing all kinds of different services to us.”

The range of the African lion (Panthera leo) is less than one-third the size that it once was. Photo by John C. Cannon

Not only will this restoration reinstall critical connections between wildlife habitats, but people stand to see benefits such as better water quality and cleaner air.

“It also, interestingly enough, empowers the individual because everybody can plant a tree or help with a wetland restoration,” Lovejoy said. “Just like a victory garden in a war effort, everybody can make a tangible contribution and it no longer seems like this impossible, unsolvable problem.

“I’m hoping that as this current young generation comes along that they’ll realize that there’s a glorious contribution to be made to the future of their descendants but also to humanity and life on Earth.”

Banner image of a giraffe (Giraffa camelopardalis tippelskirchi) in Tanzania by John C. Cannon.

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