Why Paul Ehrlich got everything wrong
And why we should still listen to warnings about environmental catastrophes
Biologist Paul Ehrlich is one of the most discredited popular intellectuals in America. He’s so discredited that his Wikipedia page starts the second paragraph with “Ehrlich became well known for the discredited 1968 book The Population Bomb”. In that book he predicted that hundreds of millions of people would starve to death in the decade to come; when no such thing happened (in the 70s or ever so far), Ehrlich’s name became sort of a household joke among the news-reading set.
And yet despite all this, in the year 2022, 60 Minutes still had Ehrlich on to offer his thoughts on wildlife loss:
When the news program was roundly ridiculed for giving Ehrlich air time, the 90-year-old scholar defended himself on Twitter by citing his academic credentials, and the fact that The Population Bomb had been peer-reviewed:
As many acidly pointed out, the fact that Ehrlich has impeccable credentials and was peer-reviewed is a reason to take a more skeptical eye toward academic credentials and peer review in general. Maybe we’ve gotten better at these things since the 60s, and maybe not. But being spectacularly wrong with the approval of a community of experts is much worse than being spectacularly wrong as a lone kook, because it means that the whole field of people we’ve entrusted to serve as experts on a topic somehow allowed itself to embrace total nonsense.
Anyway, it’s useful to review why Ehrlich got things so wrong, and why the people who make similar claims today — i.e., the “degrowth” movement — are also wrong. But it’s also important to realize that just because Ehrlich was wrong about overpopulation and some other stuff doesn’t mean that he, or the degrowth people, are wrong about the threat of habitat destruction and wildlife loss.
Why Ehrlich was so wrong in 1968
Ehrlich’s basic prediction in The Population Bomb was that overpopulation would soon cause massive famines. Matt Yglesias has a good Twitter thread with some screenshots:
And Phil Kerpen has a good thread here with some even more eye-opening silliness:
Ehrlich also predicted that 65 million Americans would starve to death in the 1980s, that England would cease to exist by the year 2000, etc. etc.
Obviously, nothing like this ever happened. But why? In fact, there are a number of reasons. But the most important principle here is just that extreme projections of recent trends tend not to come true. The scientific “models” that Ehrlich and the other enviro-catastrophists of the 60s and 70s relied on were very basic things — they were really just drawing exponential curves and then saying “See, line go up!” That sort of simple projection ignores all the various countermeasures that people will take against emerging problems, and all the ways they’ll adapt to new conditions. Countermeasures and adaptations act as a dampening force, slowing down the trend lines before catastrophe hits — sometimes, though not always, slowing it enough to avoid catastrophe entirely.
In the case of overpopulation and food supply, two big things happened to make Ehrlich wrong. The first is that a bunch of new agricultural technologies — collectively referred to as the Green Revolution — emerged that boosted crop production dramatically. For example, corn production has more than quadrupled since Ehrlich’s book came out:
The other thing that changed was the number of mouths that had to be fed. Population growth has not remained exponential; it has slowed all around the world, thanks to lower fertility rates. Ehrlich wrote right around the peak; since then, population growth has been more than cut in half.
These two factors, in combination, mean that human beings consume substantially more calories today, on average, than when Ehrlich made his sensational predictions:
Nor is this just because a few rich-world people are hogging all the food. Global deaths from hunger and malnutrition have fallen steeply, to about 212,000 in 2019:
So whether or not Ehrlich got his math right, the fact is that his assumptions were wrong. But why were they wrong? A bit of it was due to what I might call “quasi-natural” processes — economic growth led to urbanization, which drives down fertility rates. Increasing education, which also tends to accompany growth, reduced birth rates as well. But most of Ehrlich’s mistakes come from his failure to anticipate that human beings would act intentionally to avert most of the trends he was warning about.
Scientists of the 1960s, like Norman Borlaug, knew that feeding the world would be a problem as global population rose; they didn’t need Paul Ehrlich to tell them that. That’s why they dedicated their lives to working on improving crop varieties and fertilizers and irrigation. The inventors of birth control knew that for many families, having one more accidental child just meant one more mouth to feed, and they invented new forms of contraception specifically so that people could choose the family size they wanted. Human ingenuity — what Julian Simon, who famously beat Ehrlich in a bet about commodity prices, called “the ultimate resource” — was one of the stabilizing mechanisms that acted to damp out the runaway trends Ehrlich was predicting. (In fact, human ingenuity was also the reason Simon won the bet about commodities; people worked hard to develop new sources of supply and new ways of using resources more efficiently.)
Another stabilizing mechanism was government action. Concern about overpopulation was what prompted many countries to make new birth control technologies more available to their people, even when it violated their conservative values — for example, worry about food supply prompted Iran’s religious leaders to implement one of the world’s most effective (and totally voluntary) family planning programs in the 1990s.
What about coercive programs? Brutal, repressive policies like India’s mass sterilization program or China’s one-child policy were motivated in part by the overpopulation panic that originated in the West (though in China’s case the key book was The Club of Rome’s Limits to Growth). Of course, China and India hardly needed some American intellectuals to tell them that they were poor countries who struggled to feed their gigantic populations. But these were definitely the kind of brutal totalitarian measures that Ehrlich was recommending.
And yet it’s not at all clear how much of an effect these repressive policies actually had. China’s fertility rate had already declined precipitously by the time they enacted the one-child policy, and further declines didn’t happen until a decade later.
Meanwhile, India’s mass sterilization campaign in 1975 produced no discernible change in the slow, steady downward fertility trend in that country.
In other words, the stabilization mechanisms that made Ehrlich so laughably wrong were generally not the massive coercive top-down government actions that he hoped for. Instead, stabilization of global food supply was achieved via technological innovations by concerned scientists, which were then adopted by concerned governments.
There is a lesson here for the modern day.
Ehrlich’s modern-day heirs
In general, my advice to people who want to understand the late 2010s and 2020s is to read about the late 1960s and1970s. The parallels aren’t perfect, of course, but the broad-based social and political unrest that emerged in the late 60s has an obvious parallel with the unrest of the late 2010s. My general thesis is that unrest is a “macro variable” that trickles down and basically infects everything in a society, including what scientists think about and write about. For many, I think, unrest creates a sense of catastrophic runaway change, which results in a desire to “stop the bus” and slow change down. If you’re a biologist, then perhaps that fear of change manifests in catastrophic predictions about population and natural resources. Ehrlich has caught an especially large amount of flak, but he was hardly unique for his day; Mark Perry has a good roundup of apocalyptic predictions that environmentalists made around the same time, some of which are even more extreme than Ehrlich’s!
Nowadays, as in the 70s, many intellectuals on the left have become afraid of economic growth and resource limitations. This is why Ehrlich is back on TV — wildlife loss is one of the things people are scared of. But the biggest thing people worry about is climate change. And though some environmentalists have embraced the idea of green growth as the solution to climate change (which it is), there’s also a degrowth movement that’s especially popular in the UK and North Europe, and has gained a foothold in some intellectual circles in the U.S.
So far, degrowth’s popularity in the U.S. has been limited due to vigorous pushback from liberals and many leftists, who realize that its proposed solution of massive coordinated global anti-growth planning is A) unworkable, B) would stall the transition to renewable energy, and C) would require developing countries to make untenable sacrifices. But the idea still gets regular exposure in the American press, and sensible folks are forced to be constantly vigilant against the steady drumbeat of degrowtherism from across the Atlantic.
It worth mentioning, though, that degrowthers aren’t just calling for unworkable solutions; they’re also incredibly sloppy in their predictions. For example, degrowthers regularly base their assessments of unsustainable resource use on aggregate measures of material usage. Here’s a typical example:
The British intellectual Jason Hickel also uses aggregate measures of resource use by gross tonnage to support his own jeremiads against growth.
This is a terrible metric, for several reasons. First, it includes materials that are recycled or sustainable (e.g. commercial forests, or farming itself). If resources shift to a more sustainable form — for example, the massive switch from fishing to fish farming — that won’t be recorded in these numbers.
Second, it ignores one of the most important sources of sustainability: resource substitution. When humans figure out how to substitute a commonly available resource for a scarce one, sustainability increases even if the gross tonnage used also increases. For example, if we use widely available magnesium instead of scarce lithium for our batteries, that increases sustainability even if tonnage doesn’t change. Humans are always looking for ways to substitute plentiful resources for scarce ones, and we often find them.
But no matter what metric they use, degrowthers always make the same fundamental mistake, and it’s the same one Paul Ehrlich made: trend extrapolation. The tweet above is just classic “line go up” thinking. And degrowthers treat the past correlation of economic growth and resource use as if it’s a law of the Universe, when there’s no reason to believe that correlation will continue. For example, many countries have managed to decouple their carbon emissions from their GDP growth:
When confronted with this blunt fact, the degrowthers, who have long claimed that this sort of absolute decoupling is impossible, will respond that all that matters is global emissions (which is true), and that although global GDP has grown much faster than emissions since 1990, the fact that global emissions are still up slightly since that time means these have not yet decoupled in an absolute sense.
This is, of course, nonsense. Absolute decoupling in countries like Mexico, Singapore, Germany and the U.S. shows that absolute decoupling is possible in every country; most countries consume just about as much carbon as they produce, which is why outsourcing of emissions basically doesn’t happen. There’s no reason that China, India, and the rest of the world can’t decouple as well, and with them, the world. Of course, it will take several years — perhaps a decade — to demonstrate global absolute decoupling, by which time our age of unrest will likely be behind us and degrowth will have faded just as surely as the population panic of the 70s.
In the meantime, however, degrowth might push some countries’ policies in a decidedly foolish direction; I’m particularly worried about the UK. Just as India and China pursued self-destructive policies in response to the population panic, the UK may be tempted to make its grinding post-2008 stagnation even worse in the name of degrowth.
But enviro-catastrophists are not always wrong
Witnessing the follies of environmental catastrophists, from the 1970s to today, it’s tempting to conclude that people who make dire environmental predictions are simply kooks whom we should just never listen to. Indeed, many people do draw exactly that conclusion, especially on the political right. This is a bad response, for a number of reasons.
First, environmental catastrophes are a very real possibility. Climate change is the main example; if we don’t do something to limit emissions (and, probably, pull some carbon out of the air), we really do face a whole lot of extremely negative consequences. Sober scientists who believe strongly in the power of human ingenuity, technical solutions, and economic growth nevertheless recognize both the necessity and the magnitude of the task.
It would be very, very bad to ignore the people warning about climate change. If we do avert catastrophe, technology will be how we do it. But just as with Norman Borlaug, scientists have to be sufficiently worried about the problem in order to be motivated to devote their lives to this project. It’s easy to mock climate alarmism, but without some sort of alarm, people wouldn’t have spent the last 40 years figuring out how to make solar power and batteries cheap. Ingenuity is one of the great stabilizing forces of human society, but it doesn’t just happen automatically.
(So how do we tell the difference between the sober, realistic warnings and the overblown panics? There’s probably not a good general mechanism for doing this; we just have to use our intelligence to evaluate the claims various people are making. But one good rule of thumb is probably to be suspicious of people who package their warnings with pre-prepared solutions. In general, expertise in identifying a problem isn’t the same as expertise in solving it, so people who insist that mass sterilization is the only solution to overpopulation, or that degrowth is the only solution to climate change, often have a political axe to grind, or are just overconfident people to begin with.)
But there’s one other situation where prophets of enviro-doom might come in handy even when their warnings are overblown. Humans, who set all the policies and invent all the technologies, simply don’t care enough about nonhuman life. We may stop climate change and overpopulation and resource scarcity and air and water pollution out of self-interest, but it’s unlikely that pure self-interest will be enough to stop habitat destruction.
And we are destroying the animals — or at least, many of them. Wild mammals, for instance, have declined by 85% (in terms of biomass) since humans arrived on the scene. The “Living Planet Index”, which tracks the populations of over 5,000 vertebrate species, has seen a precipitous decline over the last half century:
Statistics on biodiversity and habitat loss generally all point in the same direction.
I’ll write a lot more about why this is happening, and how bad it really is, and what we can do to prevent it, but for now I’d just like to note that it’s highly unlikely that human beings care as much as we should about the welfare of non-human living beings. Some people do care, a lot; but the fact that self-interest is rarely a major factor in our calculations about other animals means that we’ll always tend to care less about actions of ours that harm those voiceless, powerless creatures.
This lack of caring can often be utterly chilling. In an otherwise strong post criticizing Ehrlich’s recent 60 Minutes appearance, Cato senior fellow Marian L. Tupy ended with this disturbing assertion:
But let’s get real. The reason the planet matters is that we are here to perceive it and to enjoy it with our senses. (Animals don’t care about biodiversity per se. What they do care about is finding an organism to kill and eat or mate with.) Moreover, the planet is not a fragile damsel in distress…Rather, it is a ruthless killing zone in need of taming.
This depiction of animals as savage beings who care only about killing and sex is strongly at odds with the experience of anyone who has actually been around animals and seen them demonstrate love, playfulness, and kindness. It also happens to omit animals’ desire to live, to avoid starvation and pain — wildlife exists not just for humans’ benefit, but for its own. And the idea that the savage necessities of life in the wild provide moral justification for human destruction of wild habitats needs some stern reexamining.
Seeing the prevalence of attitudes like this, I wonder if alarmism like Ehrlich’s isn’t a useful counterweight to human callousness. In economics jargon, perhaps overestimating the probability of a sixth mass extinction is a way to better match the private utility functions of the humans who make global economic policy with the social welfare function that includes all living, feeling beings. At the very least, alarmism might help to keep habitat destruction in the public consciousness.
So I’m not ready to throw the degrowth people and the doomers under the proverbial bus quite yet. I just want them to focus their efforts on wildlife, biodiversity, and habitat destruction, and leave climate change to more sober-minded folk.
This was such a relief to see a sane and balanced discussion of the issues. I hadn't realised the extent to which fertility declines were already occurring in China and India before the major Government interventions. But as you say, habitat destruction and loss of biodiversity are still pressing problems that have not disappeared just because we haven't had mass human starvation. I also wonder whether the social and political consequences of where rapid population growth is still occurring can be accommodated in a world where migration is such a contentious issue. As Brad DeLong shows there's plenty to go round but we're not a very sharing species.
Even if we never got more productive at farming, one thing that was never clear to me is why Erlich predicted a population combustion and mass famine, versus a situation where population asymptotically leveled off at the level of agricultural productivity. Moreover, the price mechanism and other economic forces would probably lead to a smoother and potentially higher asymptote than a situation where nothing changed but population level. For instance, increases in the relative price of arable land and food could make it such that before people would starved outright, market forces would push rural folks into denser settlements, making more room for food growth.. Meat would become relatively more expensive to grow, and shifts to cereals would increase calorie yield per hectare . Other accommodations too numerous to think of would probably occur and lead to a smoother and maybe much higher asymptote, even in the absence of the revolution in crop yields per hectare.