William Brangham:

Mother Nature is under threat from human activity as never before. More species are now threatened with extinction than at any other point in human history.

That grim assessment comes from a sweeping new report issued by a panel of experts convened by the United Nations. Among its findings, nearly a quarter of plant and animal species are threatened, many within decades. That includes more than 40 percent of amphibian species and more than a third of marine mammals.

Much of this is caused by human activity, farming and fishing and mining, as well as the use of fossil fuels that contribute to pollution and climate change. It's led to forests being cut down, and agricultural land being degraded, making large parts of the world less able to grow food.

The report says that more than a third of fish stocks are being pulled out of the oceans at unsustainable levels.

To better understand what's happening, I spoke earlier today with one of the many authors of the report. Patricia Balvanera is with the National University of Mexico. We spoke from Paris, where the report's findings were issued.

And I began by asking what she saw as the most striking part of the report.