We are stealing nature from our children.
Now, when I say this, I don't mean that we are destroying nature that they will have wanted us to preserve, although that is unfortunately also the case.
What I mean here is that we've started to define nature in a way that's so purist and so strict that under the definition we're creating for ourselves, there won't be any nature left for our children when they're adults.
But there's a fix for this.
So let me explain.
Right now, humans use half of the world to live, to grow their crops and their timber, to pasture their animals.
If you added up all the human beings, we would weigh 10 times as much as all the wild mammals put together.
We cut roads through the forest.
We have added little plastic particles to the sand on ocean beaches.
We've changed the chemistry of the soil with our artificial fertilizers.
And of course, we've changed the chemistry of the air.
So when you take your next breath, you'll be breathing in 42 percent more carbon dioxide than if you were breathing in 1750.
So all of these changes, and many others, have come to be kind of lumped together under this rubric of the "Anthropocene."
And this is a term that some geologists are suggesting we should give to our current epoch, given how pervasive human influence has been over it.
Now, it's still just a proposed epoch, but I think it's a helpful way to think about the magnitude of human influence on the planet.
So where does this put nature?
What counts as nature in a world where everything is influenced by humans?
So 25 years ago, environmental writer Bill McKibben said that because nature was a thing apart from man and because climate change meant that every centimeter of the Earth was altered by man, then nature was over.
In fact, he called his book "The End of Nature."
I disagree with this.
I just disagree with this.
I disagree with this definition of nature, because, fundamentally, we are animals.
Right?
Like, we evolved on this planet in the context of all the other animals with which we share a planet, and all the other plants, and all the other microbes.
And so I think that nature is not that which is untouched by humanity, man or woman.
I think that nature is anywhere where life thrives, anywhere where there are multiple species together, anywhere that's green and blue and thriving and filled with life and growing.
And under that definition, things look a little bit different.
Now, I understand that there are certain parts of this nature that speak to us in a special way.
Places like Yellowstone, or the Mongolian steppe, or the Great Barrier Reef or the Serengeti.
Places that we think of as kind of Edenic representations of a nature before we screwed everything up.
And in a way, they are less impacted by our day to day activities.
Many of these places have no roads or few roads, so on, like such.
But ultimately, even these Edens are deeply influenced by humans.
Now, let's just take North America, for example, since that's where we're meeting.
So between about 15,000 years ago when people first came here, they started a process of interacting with the nature that led to the extinction of a big slew of large-bodied animals, from the mastodon to the giant ground sloth, saber-toothed cats, all of these cool animals that unfortunately are no longer with us.
And when those animals went extinct, you know, the ecosystems didn't stand still.
Massive ripple effects changed grasslands into forests, changed the composition of forest from one tree to another.
So even in these Edens, even in these perfect-looking places that seem to remind us of a past before humans, we're essentially looking at a humanized landscape.
Not just these prehistoric humans, but historical humans, indigenous people all the way up until the moment when the first colonizers showed up.
And the case is the same for the other continents as well.
Humans have just been involved in nature in a very influential way for a very long time.
Now, just recently, someone told me, "Oh, but there are still wild places."
And I said, "Where?
Where?
I want to go."
And he said, "The Amazon."
And I was like, "Oh, the Amazon.
I was just there.
It's awesome.
National Geographic sent me to Manú National Park, which is in the Peruvian Amazon, but it's a big chunk of rainforest, uncleared, no roads, protected as a national park, one of the most, in fact, biodiverse parks in the world.
And when I got in there with my canoe, what did I find, but people.
People have been living there for hundreds and thousands of years.
People live there, and they don't just float over the jungle.
They have a meaningful relationship with the landscape.
They hunt.
They grow crops.
They domesticate crops.
They use the natural resources to build their houses, to thatch their houses.
They even make pets out of animals that we consider to be wild animals.
These people are there and they're interacting with the environment in a way that's really meaningful and that you can see in the environment.
Now, I was with an anthropologist on this trip, and he told me, as we were floating down the river, he said, "There are no demographic voids in the Amazon."
This statement has really stuck with me, because what it means is that the whole Amazon is like this.
There's people everywhere.
And many other tropical forests are the same, and not just tropical forests.
People have influenced ecosystems in the past, and they continue to influence them in the present, even in places where they're harder to notice.
So, if all of the definitions of nature that we might want to use that involve it being untouched by humanity or not having people in it, if all of those actually give us a result where we don't have any nature, then maybe they're the wrong definitions.
Maybe we should define it by the presence of multiple species, by the presence of a thriving life.
Now, if we do it that way, what do we get?
Well, it's this kind of miracle.
All of a sudden, there's nature all around us.
All of a sudden, we see this Monarch caterpillar munching on this plant, and we realize that there it is, and it's in this empty lot in Chattanooga.
And look at this empty lot.
I mean, there's, like, probably, a dozen, minimum, plant species growing there, supporting all kinds of insect life, and this is a completely unmanaged space, a completely wild space.
This is a kind of wild nature right under our nose, that we don't even notice.
And there's an interesting little paradox, too.
So this nature, this kind of wild, untended part of our urban, peri-urban, suburban agricultural existence that flies under the radar, it's arguably more wild than a national park, because national parks are very carefully managed in the 21st century.
Crater Lake in southern Oregon, which is my closest national park, is a beautiful example of a landscape that seems to be coming out of the past.
But they're managing it carefully.
One of the issues they have now is white bark pine die-off.
White bark pine is a beautiful, charismatic -- I'll say it's a charismatic megaflora that grows up at high altitude -- and it's got all these problems right now with disease.
There's a blister rust that was introduced, bark beetle.
So to deal with this, the park service has been planting rust-resistant white bark pine seedlings in the park, even in areas that they are otherwise managing as wilderness.
And they're also putting out beetle repellent in key areas as I saw last time I went hiking there.
And this kind of thing is really much more common than you would think.
National parks are heavily managed.
The wildlife is kept to a certain population size and structure.
Fires are suppressed.
Fires are started.
Non-native species are removed.
Native species are reintroduced.
And in fact, I took a look, and Banff National Park is doing all of the things I just listed: suppressing fire, having fire, radio-collaring wolves, reintroducing bison.
It takes a lot of work to make these places look untouched.
(Laughter) (Applause) And in a further irony, these places that we love the most are the places that we love a little too hard, sometimes.
A lot of us like to go there, and because we're managing them to be stable in the face of a changing planet, they often are becoming more fragile over time.
Which means that they're the absolute worst places to take your children on vacation, because you can't do anything there.
You can't climb the trees.
You can't fish the fish.
You can't make a campfire out in the middle of nowhere.
You can't take home the pinecones.
There are so many rules and restrictions that from a child's point of view, this is, like, the worst nature ever.
Because children don't want to hike through a beautiful landscape for five hours and then look at a beautiful view.
That's maybe what we want to do as adults, but what kids want to do is hunker down in one spot and just tinker with it, just work with it, just pick it up, build a house, build a fort, do something like that.
Additionally, these sort of Edenic places are often distant from where people live.
And they're expensive to get to.
They're hard to visit.
So this means that they're only available to the elites, and that's a real problem.
The Nature Conservancy did a survey of young people, and they asked them, how often do you spend time outdoors?
And only two out of five spent time outdoors at least once a week.
The other three out of five were just staying inside.
And when they asked them why, what are the barriers to going outside, the response of 61 percent was, "There are no natural areas near my home."
And this is crazy.
This is just patently false.
I mean, 71 percent of people in the US live within a 10-minute walk of a city park.
And I'm sure the figures are similar in other countries.
And that doesn't even count your back garden, the urban creek, the empty lot.
Everybody lives near nature.
Every kid lives near nature.
We've just somehow forgotten how to see it.
We've spent too much time watching David Attenborough documentaries where the nature is really sexy -- (Laughter) and we've forgotten how to see the nature that is literally right outside our door, the nature of the street tree.
So here's an example: Philadelphia.
There's this cool elevated railway that you can see from the ground, that's been abandoned.
Now, this may sound like the beginning of the High Line story in Manhattan, and it's very similar, except they haven't developed this into a park yet, although they're working on it.
So for now, it's still this little sort of secret wilderness in the heart of Philadelphia, and if you know where the hole is in the chain-link fence, you can scramble up to the top and you can find this completely wild meadow just floating above the city of Philadelphia.
Every single one of these plants grew from a seed that planted itself there.
This is completely autonomous, self-willed nature.
And it's right in the middle of the city.
And they've sent people up there to do sort of biosurveys, and there are over 50 plant species up there.
And it's not just plants.
This is an ecosystem, a functioning ecosystem.
It's creating soil.
It's sequestering carbon.
There's pollination going on.
I mean, this is really an ecosystem.
So scientists have started calling ecosystems like these "novel ecosystems," because they're often dominated by non-native species, and because they're just super weird.
They're just unlike anything we've ever seen before.
For so long, we dismissed all these novel ecosystems as trash.
We're talking about regrown agricultural fields, timber plantations that are not being managed on a day-to-day basis, second-growth forests generally, the entire East Coast, where after agriculture moved west, the forest sprung up.
And of course, pretty much all of Hawaii, where novel ecosystems are the norm, where exotic species totally dominate.
This forest here has Queensland maple, it has sword ferns from Southeast Asia.
You can make your own novel ecosystem, too.
It's really simple.
You just stop mowing your lawn.
(Laughter) Ilkka Hanski was an ecologist in Finland, and he did this experiment himself.
He just stopped mowing his lawn, and after a few years, he had some grad students come, and they did sort of a bio-blitz of his backyard, and they found 375 plant species, including two endangered species.
So when you're up there on that future High Line of Philadelphia, surrounded by this wildness, surrounded by this diversity, this abundance, this vibrance, you can look over the side and you can see a local playground for a local school, and that's what it looks like.
These children have, that -- You know, under my definition, there's a lot of the planet that counts as nature, but this would be one of the few places that wouldn't count as nature.
There's nothing there except humans, no other plants, no other animals.
And what I really wanted to do was just, like, throw a ladder over the side and get all these kids to come up with me into this cool meadow.
In a way, I feel like this is the choice that faces us.
If we dismiss these new natures as not acceptable or trashy or no good, we might as well just pave them over.
And in a world where everything is changing, we need to be very careful about how we define nature.
In order not to steal it from our children, we have to do two things.
First, we cannot define nature as that which is untouched.
This never made any sense anyway.
Nature has not been untouched for thousands of years.
And it excludes most of the nature that most people can visit and have a relationship with, including only nature that children cannot touch.
Which brings me to the second thing that we have to do, which is that we have to let children touch nature, because that which is untouched is unloved.
(Applause) We face some pretty grim environmental challenges on this planet.
Climate change is among them.
There's others too: habitat loss is my favorite thing to freak out about in the middle of the night.
But in order to solve them, we need people -- smart, dedicated people -- who care about nature.
And the only way we're going to raise up a generation of people who care about nature is by letting them touch nature.
I have a Fort Theory of Ecology, Fort Theory of Conservation.
Every ecologist I know, every conservation biologist I know, every conservation professional I know, built forts when they were kids.
If we have a generation that doesn't know how to build a fort, we'll have a generation that doesn't know how to care about nature.
And I don't want to be the one to tell this kid, who is on a special program that takes Philadelphia kids from poor neighborhoods and takes them to city parks, I don't want to be the one to tell him that the flower he's holding is a non-native invasive weed that he should throw away as trash.
I think I would much rather learn from this boy that no matter where this plant comes from, it is beautiful, and it deserves to be touched and appreciated.
Thank you.
(Applause)