04/23/2014 04:27 pm ET Updated Jun 23, 2014

Are We in the Early Stages of a New Mass Extinction? It's Complicated

Tom Stoddart via Getty Images

If you stay awake at night wondering about the worst thing that could ever happen, I have an answer for you. It's called a mass extinction. Basically, it's a real-life apocalypse, where over 75 percent of all species on the planet die out over a million years -- a blink of an eye in geological time. Now there's mounting evidence that we're entering a new mass extinction today.

Over the past half-billion years that life has wandered across our planet, we've already suffered through five mass extinctions. You've probably heard about the most famous mass extinction, which happened about 65 million years ago at the end of the Cretaceous period when an asteroid smashed into the planet and wiped out most of the dinosaurs. In previous mass extinctions, however, there were equally impressive natural disasters, ranging from rapid ice ages and continent-wide wildfires, to mega-volcanoes. In each of these catastrophes, most life in the world died out, replaced over the next few million years by whole new ecosystems of animals and plants. No matter how much of the planet burned or was buried in ice, life rose again.

When I was researching my book, Scatter Adapt and Remember: Humans Will Survive a Mass Extinction, I talked to a lot of scientists about a fundamental mystery -- how any did any animals and plants make it through these devastating times? Their answers gave me a window on what it would have been like to live through one of these mass extinctions. What became clear right away was that these disasters all have one thing in common. No matter what their initial causes, they ultimately killed so many life forms with climate and habitat changes. Even the asteroid that took out the dinosaurs did most of its damage to life not from an instant flash-cooking of the planet, but during the long nuclear winter that followed. All the debris from the meteor impact shot into the upper atmosphere, creating thick clouds that blotted out the sun and decimated plant life. And that changed ecosystems all across Earth.

If you were one of the animals who survived that catastrophic explosion and had to face the changes that followed, you would have seen a world that was dying with a whimper. Climate changes are devastating because they destroy the food webs that link every life form on the planet in a network of eaters and eaten. When sunlight was blocked by a cloud layer 65 million years ago, a primary source of food died with all those plants. Then the herbivores, plant eaters, began to starve; and the carnivores starved when their prey succumbed to famine too.

Among the survivors were animals who could adapt quickly to their new environments, spreading out into new territories unlike anything they'd dealt with before. Life would have been a series of constant, unpleasant surprises for the small, furry shrew-like mammals who made it beyond the Cretaceous. Part of their adaptability involved being able to eat a variety of foods. This trait would come in handy during an era when food sources were unstable and changing rapidly.

No matter what set off these mass extinctions -- and there's reason to believe that most of them had multiple causes -- they all ended the same way. Millions of species died because their habitats changed, which caused their food sources to disappear. Mass extinctions are nothing like the glorified super-cleanse of a mythical apocalypse. They are ugly, slow, and terribly complicated.

There are many signs today that we may be in the early stages of a new mass extinction. The climate is changing very rapidly, plus we're seeing an extraordinary number of extinctions among land animals. It's possible that this sixth mass extinction cycle began roughly 15,000 years ago, with the dieoffs of megafauna like mammoths and giant sloths in the Americas.

Are we doomed? I don't think so. Unlike animals who lived through previous mass extinctions, humans can actually see it coming. Using science, we can study previous mass extinction survivors and learn from them what we'll need to survive -- and perhaps even prevent the worst effects of the next catastrophic wave of extinctions. One of humanity's greatest strengths is our adaptability. We've spread out into every corner of the planet, making icy mountains and arid deserts into our homes. Best of all, we are capable of planning for the future, and making changes now that will benefit our species in centuries to come.

Given what we know of previous mass extinction scenarios, it's clear that our biggest dangers come from habitat changes that undermine food security. So our first step toward survival has to be exploring alternative fuels that don't load our atmosphere with habitat-changing carbon. In previous mass extinctions, volcanoes and fires did the work of our industrial revolution, raising temperatures and ocean acidity without any human intervention. This time around, we need to intervene, and fast. By reducing carbon emissions, we can slow down the changes that will eventually destroy our food supplies.

When thinking about the future of our survival, I often consider the words of one mass extinction expert I spoke with. A quiet man named Peter Roopnarine, he works at the California Academy of Sciences, researching now-extinct food webs. Essentially, he studies what happens when a mass extinction is making the world starve. He told me that death is what leads to death. The more life forms go extinct, the more knock-on extinctions you'll get from that fraying food web. He believes that maybe there's a tipping point, perhaps around the time when 40 percent of all species have died out, when the death toll rises in a sudden spike and hits that 75 mark that's the gateway to a mass extinction event.

Death is what leads to death. When animals and plants go extinct around us, each one causes more extinctions. But the flip side is also true. Mass extinctions do not happen overnight. Each step we take toward saving our environments and the lives in them, the closer we come to saving the world -- and ourselves.

I talk about the small (and giant) steps we can take to create a more survivable future for humanity in my book, Scatter, Adapt and Remember: How Humans Will Survive a Mass Extinction.