Dr. Losos also noted that giving precise estimates of wildlife populations was difficult, in part because scientists do not always agree on what defines a population, which makes the question inherently subjective.

Despite those issues, Dr. Losos said, “I think it’s a very important and troubling paper that documents that the problems we have with biodiversity are much greater than commonly thought.”

The authors of the paper suggest that previous estimates of global extinction rates have been too low, in part because scientists have been too focused on complete extinction of a species. Two vertebrate species are estimated to go extinct every year, which the authors wrote “does not generate enough public concern,” and lends the impression that many species are not severely threatened, or that mass extinction is a distant catastrophe.

Conservatively, scientists estimate that 200 species have gone extinct in the past 100 years; the “normal” extinction rate over the past two million years has been that two species go extinct every 100 years because of evolutionary and other factors.

Rather than extinctions, the paper looks at how populations are doing: the disappearance of entire populations, and the decrease of the number of individuals within a population. Over all, they found this phenomenon is occurring globally, but that tropical regions, which have the greatest biodiversity, are experiencing the greatest loss in numbers, and that temperate regions are seeing higher proportions of population loss. Dr. Ehrlich, who rose to prominence in the 1960s after he wrote “The Population Bomb,” a book that predicted the imminent collapse of humanity because of overpopulation, said he saw a similar phenomenon in the animal world as a result of human activity.

“There is only one overall solution, and that is to reduce the scale of the human enterprise,” he said. “Population growth and increasing consumption among the rich is driving it.”

He and Dr. Ceballos said that habitat destruction — deforestation for agriculture, for example — and pollution were the primary culprits, but that climate change exacerbates both problems. Accelerating deforestation and rising carbon pollution are likely to make climate change worse, which could have disastrous consequences for the ability of many species to survive on earth.