"The serious warning in our paper needs to be heeded because civilization depends utterly on the plants, animals, and microorganisms of Earth that supply it with essential ecosystem services."
—Paul Ehrlich, Stanford University

A new study published in the Proceedings of the National Academy of Sciences on Monday argues based on "current trends of population declines and extinctions" that we are currently witnessing Earth's "sixth mass extinction."

"Population extinctions today are orders of magnitude more frequent than species extinctions," the study's authors—scientists Gerardo Ceballos, Paul Ehrlich, and Rodolfo Dirzo—argue.

They continue:

When considering this frightening assault on the foundations of human civilization, one must never forget that Earth's capacity to support life, including human life, has been shaped by life itself. When public mention is made of the extinction crisis, it usually focuses on a few animal species (hundreds out of millions) known to have gone extinct, and projecting many more extinctions in the future. But a glance at our maps presents a much more realistic picture: they suggest that as much as 50% of the number of animal individuals that once shared Earth with us are already gone, as are billions of populations. Furthermore, our analysis is conservative, given the increasing trajectories of the drivers of extinction and their synergistic effects.

The scientists suggest that while multiple factors have contributed to the "biological annihilation" that has accelerated rapidly in recent decades, "the ultimate drivers" are "human overpopulation and continued population growth, and overconsumption, especially by the rich."

Given that "the sixth mass extinction is already here" and not merely a dire possibility to be guarded against in the distant future, "the window for effective action is very short, probably two or three decades at most," the scientists write.

"All signs point to ever more powerful assaults on biodiversity in the next two decades, painting a dismal picture of the future of life, including human life," they conclude.

Acknowledging the warnings of researchers wary of "overstating the science in a way that presents the problem as unsolvable," Ceballos, Ehrlich, and Dirzo insist that their dire message is an urgent call to action, not an expression of doom-and-gloom defeatism.

Ehrlich, speaking with the Guardian, argued that the use of "strong language" is in this case warranted by the science.

"The serious warning in our paper needs to be heeded because civilization depends utterly on the plants, animals, and microorganisms of Earth that supply it with essential ecosystem services ranging from crop pollination and protection to supplying food from the sea and maintaining a livable climate," he said.

"The time to act is very short," Ceballos added.