For a scholar who traffics in some of the more dispiriting elements of modern biology, ecology and demographics, Paul R. Ehrlich is a remarkably funny guy. His caption for this picture? “A living Neanderthal” contemplating the skull (a replica) of an extinct one. Maybe his humor is a coping mechanism for the parlous state of the planet; maybe it’s the result of more than 50 years as a Stanford University researcher, professor and author.

However you draw the map of this melting, freezing world, Ehrlich is on it. He got there in 1968, with the sizzlingly, and to Ehrlich’s mind now, regrettably titled book “The Population Bomb.” It is replete with “ifs” and “whens” about the catastrophic collision of population versus resources, some of which have come to pass and some of which haven’t -- yet. On that score, Ehrlich is as gleeful at attacking his critics as they are at going after him.

In his latest book, “Humanity on a Tightrope,” coauthored with Robert E. Ornstein, the tightrope could still turn into a lifeline if humans choose the right balance. Before he’s off to Costa Rica to pursue his first academic love, butterflies, he’s looking the planet, and humanity, in the face.

One thing I draw from your new book is that you’re now calling on individuals to do what institutions have failed to when it comes to saving the planet and ourselves.

That’s part of it. We now know more than enough about what the hell is wrong with the world. The climate, the toxification of the planet, the epidemiological environment, the chances of plague, losing biodiversity, the rate of extinction of species -- and we’re doing nothing about it. We’ve had 10 failures now on international attempts to do something about climate change. If we don’t figure out how to change human behavior toward sustainability, we’re basically ? screwed, I think is the technical term.

There’s a mechanical model of what’s happening to the world: Go into the smallest room of your house, and attached to the floor is a porcelain thing, and if you raise the lid on it and then you look into the bowl and press one of the levers, it will show you what’s happening to the environment.

“The Population Bomb,” which you and your wife, Anne, wrote more than 40 years ago, includes scenarios that haven’t happened. Critics throw these back at you to prove you were wrong then and to suggest you are wrong now.

Scientists live by their reputations with their colleagues, not with Rush Limbaugh and Sarah Palin. I’m attacked almost daily on the blogs.

When we wrote it, there were about 3.5 billion people on the planet; about half a billion of them were hungry. Today there are 7 billion people on the planet and about a billion of them are hungry. We’ve lost something on the order of 200 million to 400 million to starvation and diseases related to starvation since the book was written. How “wrong” [were] we?

Of course all our predictions were not correct, but a lot of the stuff they say were predictions were scenarios where we said: These are not predictions; these are stories to make you think about the future.

We’d write an entirely different book [today]. We didn’t know anything [then] about ozone depletion, what the threat was. The climatologists weren’t sure whether it was going to be a problem of more cold or more heat. What we said is, if you’re putting crap into the atmosphere, you’re going to change the climate.

We mentioned the possibility of having to kayak to the Washington Monument; we also talked about the possibility of [global] cooling. We didn’t know what was happening to the tropical forests. There’s very little in the book on biodiversity [risks] because the work hadn’t been done yet.

What was crystal clear then and is crystal clear today is that one of the major factors is the size of the human population. The I = P x A x T equation -- [human] impact is the product of the number of people, how much each one consumes and the technologies we use for consumption.

People are uncomfortable talking about population -- it brings up such intimate choices and the specter of government control over who procreates -- but they will talk about consumption. Does that address the problem more palatably?

Everybody who can count up to 20 without taking off their shoes is aware there’s a population problem. But most politicians and many economists still think that more consumption is the cure for everything rather than part of the disease.

We know we can change our consumption habits very nearly overnight: In 1941, the U.S. produced almost 4 million passenger cars. Then came Dec. 7, and for the next several years we produced millions of military vehicles, tanks, trucks, thousands of military aircraft and ships, developed nuclear weapons and detonated them, rationed rubber, sugar, coffee, gasoline -- showing that if the incentives are right, [we] can change our consumption patterns, including the way industry works, basically overnight.

When people said Al Gore was crazy when he said we could [quickly] get all of our electricity without using coal, he was saying something that was politically impractical, but it was certainly possible. My research is going into cultural evolution; how you change the way we behave in order to get a sustainable society, when we’re moving in the opposite direction.

Is the Obama administration’s science leadership on board with this?

Probably. There’s never been better science advice in the U.S. government. Obama knows what to do too.

I hear a “but” lurking in there.

This is obviously opinion, but a major problem is that we have corporations now considered to be individuals like you and me. The idea that corporations should have free speech, I think, is insane. The free speech of the corporations is the petroleum industry and their buddies setting up entire institutions to lie to the public about fossil fuels and so on. I’m pretty depressed about that.

If you think that corporations should be treated as individuals, then there’s a whole slug of corporations that ought to be in Guantanamo right now being waterboarded.

Still, you sound more optimistic than I am that we can save the day.

[He laughs.] It used to be when people said, “Are you optimistic or pessimistic?,” I’d say, I’m pessimistic about where we’re going, but I’m optimistic about what we can do. Now I say: I’m very pessimistic about where we’re going, and I’m optimistic about what we could do, but I don’t expect it to happen. It’s a real problem talking to kids. How do you strike the balance? What I usually say is look, there’s a 15% chance of preventing the collapse of civilization, if we work at it really hard.

What about the word “conserve” do you think some conservatives don’t understand?

I am in many respects a conservative. The idea is to pay attention to what’s worked in the past and don’t throw those things away until you’re pretty damned sure that what you’re replacing them with is going to be better.

Human empathy is something you pin your hopes on in the new book. But to me, the sci-fi trope -- until the aliens arrive, humans will always find reasons to fight each other -- is pretty true.

One of the cheery things I think, and you haven’t heard a lot of cheer from me, is we have the built-in capacity to put ourselves in others’ shoes. The issue is, can we spread that empathy to 7 billion people? Just in my lifetime, we’ve spread empathy, making more “us” and fewer “them.” If we had another 1,000 years, I’d be an optimist! I’d be saying, well things are going in the right direction, slowly, and by my great-great grandchildren, things could be pretty good. I have a great-granddaughter now; that child is not facing a great world.

You practiced what you preach and had a vasectomy after having one child. Aren’t most people only going to do what is convenient and cheap?

I think lots of people are willing to do more but just can’t believe it’s going to do any good. That’s a real problem: You can see what needs to be done, but you say, if I give up meat eating, what difference is it going to make? We are fundamentally social animals, and we’ve got to organize ourselves into groups. There’s lots of groups trying to do good things.

Part of the blame is [on] what we’ve let happen to our public education system. Think about it -- you can get all the way through most California schools and then get a PhD at Stanford and not have a clue where your food comes from -- [you can] think it comes from the supermarket.

People are desperately trying to spend time getting more income; people don’t have any idea about nature now. They think seeing a film about the Serengeti wildebeest migration is equivalent to being there.

You’ve got to spend time in nature, and that means more than watching a film. It’s not that nature films aren’t important; it’s that they’re not a substitute. You can have a great time in your own backyard. You can interface with nature even in some of the most hideous areas in the world. Jared [Diamond, Ehrlich’s bird-watching buddy and an author] lives in Los Angeles, which is hardly even inhabitable!

Hey, watch it there.

Just teasing!

One problem ecologists have talking to the general public is that we tend to think in much longer terms than the average economist and even the average person. The average person is concerned with everyday affairs, and to a large extent rightly so, but they’ve got to [make] some time for the longer term, if they care about their children and grandchildren.

What practical efforts to keep population down would work? I hate to get phallic about it, but how much carrot and how much stick?

Population is the background driver. The standard line, which I really agree with, is, whatever your cause, it’s a lost cause without population control.

First, you work on the rights of women -- job opportunities for women, education, giving women rights -- and in most parts of the world, that would get us where we want to be, a gradual population decline over the next century.

And you get some leadership. If an American president got up and said, “Patriotic Americans stop at two [children]” -- that’s where you need some guts. Consumption is equally important. I’d think the biggest problem is figuring out what to do on consumption. We don’t have any consumption condoms.

patt.morrison@latimes.com

This interview was edited and excerpted from a longer taped transcript. Interview archive: latimes.com/pattasks.