Fewer Feet, Smaller Footprint
Hello everyone:
First a quick announcement: A book I’ve helped put together has just been published. The Little Things: A Memoir of Paralysis, Motivation, and Pursuing a Meaningful Life is Jack Trottier’s powerful and beautiful story of a promising young athlete finding new life from the seat of a wheelchair. It is, as the Boston Globe just noted in a strong review, “soul-lifting, and worthy of admiration.” Jack is a truly remarkable guy, and it was a privilege to work with him on the book. You can order it from your bookstore, or online from the publisher and the usual vendors.
Here is this week’s curated Anthropocene news:
The Pandemic and the Atmosphere: The hiatus in global human activity during the height of the pandemic created a remarkable opportunity to study how the Earth’s atmosphere responded to the reduction in emissions and air pollution. The results, though, were surprising.
Shifting the Goal Posts for Conservation: Climate change will increasingly distort ecosystems around the world, so conservationists are strategizing to understand what to preserve in order to provide safe haven for species in limbo or on the move. This is happening in the context of the ambitious “30 x 30” goal: protecting 30% of Earth’s terrestrial and ocean environments by 2030.
Climate Boon or Boondoggle?: An excellent comprehensive article in Mother Jones analyzing whether CO2-sucking technology will be vital to reducing emissions or is just another delaying tactic by the fossil fuel industry.
An Otter Solution: More sea otters eat more invasive urchins, the absence of which helps restore kelp forests, which are one of the best natural solutions for CO2 sequestration. Kelp forests around the world have been devastated – California has lost 95% – and bringing back otters is a win-win for biodiversity and climate. And cuteness.
Now on to this week’s (less cute) essay:
The constraints of the biosphere are fixed. The bottleneck through which we are passing is real. It should be obvious to anyone not in a euphoric delirium that whatever humanity does or does not do, Earth's capacity to support our species is approaching the limit.
Observant readers will remember E.O. Wilson’s words above from my essay on human population back in September (it’s an excerpt from his 2002 book The Future of Life). Wilson’s warning is my starting point this week because I want to talk a bit about the notion of Earth’s capacity to host modern humans, and about the limit that Wilson mentions.
David Farrier opens his beautiful book, Footprints: In Search of Future Fossils, with the remarkable discovery on Happisburgh beach in southeastern England of a trove of 850,000-year-old fossil human footprints in soft sediment, arrayed like a “step map of a frantic dance floor.” The prints were made by a group of human ancestors known now as Homo antecessor as they walked southward along what had been the mudflats of an estuary. Farrier sees the footprints as
an enchanting glimpse of ancestors whose past seems to brush against our present… Even in photographs they conjure the uncanny sensation that the group has only just left, their prints fresh and glistening – that we could catch them, if only we hurried.
Geologically speaking, we will join them soon enough. 850,000 years is nothing in the ages of the Earth, and millennia from now we will have left our Anthropocene footprints to rest atop theirs in a world we will shape but can little imagine. Remember that the geological signature of our modern age is the main point of the Anthropocene label. We will leave not merely a transient dance floor but the mosh pit marks of billions of people toying with nuclear weapons, fossil fuels, transcontinental highways, and mass extinction.
The Happisburgh footprints washed away after two weeks.
It’s been estimated that the Earth’s carrying capacity – defined by the resource limits of the environment – for a world full of hunter-gatherers would be about 100 million people. That is, more than a hundred million hunter-gatherers (particularly the hunters) would be unsustainable, and would collapse the ecosystems they relied upon. This estimate assumes the use of stone tools and other means of more efficiently hunting and harvesting game. Without those tools, the capacity is assumed to be much lower, in the tens of millions.
And that’s a key point here. The more we’ve upgraded our tools (I mean this broadly, from agriculture to information), the more we’ve distorted the landscape to provide food, water, shelter, fuel, and luxuries for our species-specific purposes. And the more we’ve concentrated our efforts to throw entire ecosystems into the blender, the more of us we could sustain. This is our modern history. From the viewpoint of life on Earth, this constant growth and its attendant destruction is the main feature of our civilization.
As critics of the carrying capacity concept are fond of saying, we’ve been modifying the landscape to successfully increase our population for thousands of years. From metal tools to the Green Revolution to GMOs and satellite-based crop monitoring, they point out, the technological progress has been astonishing. I would suggest, though, that it’s less astonishing than the resulting collapse of ecosystems around the world, most of which has occurred in the last century. Awe at the global rise of a single species seems questionable, if not hasty, if that rise comes at the cost of a million other species we depend upon.
The debate, then, is on whether there are limits, what they are, and whether we’ve passed them already. Wilson, in his 2002 phrase, “approaching the limit,” was hedging his bets, I think. Understanding exactly what the limits might be is extraordinarily difficult, as is defining their parameters. The two questions are inextricable – the number of Anthropocene humans that fit on the planet is defined in part by what kind of planet we want to live on – so I’ll pick away at them together.
I have a very strong bias here, so I’ll name it. A discussion about carrying capacity isn’t worth having if we’re not also talking about maintaining a lush, diverse Earth all around us. This is not the idiocy of “How many college students can we fit into a phone booth?” writ large, in an abstract math exercise that imagines humans as the only meaningful species on Earth. This is “How do we restore global ecosystems and live within or alongside them?” A calculation of maximum population is useless because it’s not based in the reality of our dependence on a healthy planet. The calculation I’m after is of optimum population governed by the needs of humans and the rest of life on Earth.
In other words, it’s not simply how many people can we fit or feed, it’s how many should we fit or feed? And that is a question that many people simply hate, because it appears to challenge human freedom, dignity, and optimism. And it’s a question that nearly everyone, even advocates for reducing population, has trouble answering. No one really knows the number. There’s neither precedent nor map to guide us.
But a lack of conclusion hasn’t stopped the guessing. Nor has the unethical irrelevance of a maximum population calculation. As seen in the quirky graphic above, a 2012 UN Environment Program survey (“One Planet, How Many People?”) of carrying capacity estimates found a wildly disparate set of numbers, from half a billion to – I can’t believe I’m writing this – one trillion humans. Fully half of the 65 estimates were in the 16 billion to 1 trillion range, while another twenty agreed that 8 billion was a good guess. Clearly that’s 8 billion humans living quite differently than we are, since we and our livestock make up 96% of mammal biomass on Earth and we’ve altered at least 70% of the land for our purposes. Already we use up the production equivalent of 1.7 Earths each year. If everyone lived like an American we’d consume the equivalent of five Earths.
Among those advocating for a lower carrying capacity, a 2020 book by an American geographer put optimum population at 3 billion, and a 2021 book by a Cambridge University economist suggested a range of half a billion to 5 billion, depending on the level of resource use. The UK’s Optimum Population Trust (OPT) landed on 5 billion, with the caveat that the number will decline as conditions worsen. The remarkable and remarkably idiosyncratic James Lovelock, who with Lynne Margulis conceived the Gaia hypothesis, thinks half a billion to a billion is about right to reinstate the natural order of things. A classic study in 1994 by Paul Erlich, Anne Erlich, and Gretchen Daily estimated optimum population to be 1.5 to 2 billion. 1994 was a long time ago, but in a 2018 Guardian interview Erlich reiterated the estimate and agreed with the OPT that a sustainable population figure was likely to shrink as the 21st century brought more environmental degradation: “The longer humanity pursues business as usual, the smaller the sustainable society is likely to prove to be. We’re continuously harvesting the low-hanging fruit, for example by driving fisheries stocks to extinction.”
This warning from the science community has been around for a while. Does anyone remember the “1992 World Scientists’ Warning to Humanity”? It was signed by “1,700 of the world's leading scientists, including the majority of Nobel laureates in the sciences.” They vouched for the idea of carrying capacity in the strongest terms:
The earth is finite. Its ability to absorb wastes and destructive effluent is finite. Its ability to provide food and energy is finite. Its ability to provide for growing numbers of people is finite. And we are fast approaching many of the earth's limits. Current economic practices which damage the environment, in both developed and underdeveloped nations, cannot be continued without the risk that vital global systems will be damaged beyond repair. Pressures resulting from unrestrained population growth put demands on the natural world that can overwhelm any efforts to achieve a sustainable future. If we are to halt the destruction of our environment, we must accept limits to that growth.
And they made five recommendations, two of which speak directly to carrying capacity: “We must stabilize population,” and “We must ensure sexual equality, and guarantee women control over their own reproductive decisions.”
Since their letter was written, some good work has been done globally to provide education for girls and family planning services for women. In parallel with education rates and levels of affluence, fertility rates have dropped across the globe. Population growth rate has halved from its 2.09% peak in the late 1960s to 1.05% today, but population has still increased from 5.4 to nearly 8 billion. Growth is faster now (about 81 million additional humans per year) than at the peak (72 million/year) because 1.05% of nearly 8 billion still adds up to an annual Germany of babies. Before 1950, no one had experienced a doubling of our population, but anyone born in 1950 or earlier has now experienced at least a tripling of our numbers. If you’re 95 and reading this, population has quadrupled since you were born.
And whatever we might categorize as progress, moreover, has come with catastrophic changes to life on Earth. We’ve cut the planet’s plant production in half, eliminated 85% of wetlands, compromised about two thirds of the oceans, dammed over 75% of the world’s large rivers, produced a mass of plastics greater than that of all land and sea animals combined, and are pushing millions of species toward extinction.
And yet the critics of carrying capacity persist, resting much of their argument on the continuum of human adaptation throughout our species’ brief history. We controlled fire and developed agriculture, we invented artificial nitrogen and urban architecture, and we’ve cracked the code of genomes and artificial intelligence. So far, so good!, they say, believing that we will continue to solve the growth puzzle even as we somehow make the world a better place for all people and ecosystems.
A 2013 New York Times op-ed by an ecologist called the idea of a carrying capacity crisis “nonsense,” noting that as our population increases in number and density we’ve always become more productive and efficient. And a 2018 Aeon essay by Ted Nordhaus, a prominent progressive environmentalist, suggested that restricting us to planetary limits is akin to treating humans like livestock or insects. Which is funny, since our relationships with livestock and insects both provide good data on why population is a problem, with the uncertain fate of insects largely tied to the fate of the landscapes fenced off for grazing or plowed under and soaked in pesticides and herbicides for monocultural agriculture to feed the livestock. Both arguments, to me at least, sound like those of high-functioning addicts, very intelligent humans who insist that what we’re doing, while ecologically glitchy, is both necessary and amazing, and that we’ll sort out the glitches somehow. Soon, we promise.
The Aeon piece argues, weirdly, against carrying capacity with the suggestion that we can keep going and fill a stripped-down Earth with “chickens, corn, and nuclear power,” creating a world that “might not be the idyll that many wish for, but it would clearly be one that would be capable of supporting a lot more people consuming a lot more stuff for a very long time.” And in a climactic, irrational, ode to the Anthropocene, Nordhaus says this:
“To understand the human experience on the planet is to understand that we have remade the planet again and again to serve our needs and our dreams. Today, the aspirations of billions depend upon continuing to do just that. May it be so.”
The freedom to enjoy continual growth is the noblest cause for some critics. (Paul Erlich, on the other hand, likes to say that “perpetual growth is the creed of the cancer cell.”) In order to sneak around planetary limits, they believe, we’ll figure out a way to feed more people and use resources more efficiently. We’ll make civilization a fairer place, sharing resources equitably, so that affluent and powerful nations don’t consume too much. We’ll grow food in factories, we’ll eat less meat, we’ll move into cities, etc.
These are admirable goals in the face of the climate and biodiversity crises, but we should do them all anyway while setting all of civilization the task of regenerating biodiversity. But another Germany of babies every year in the midst of an ever-harsher climate, an acidifying ocean, wounded ecosystems, and the likelihood of growing political chaos will make improving the human condition and restoring the natural world that much harder.
In the face of all this, it makes sense to me to actively reduce population by accelerating the voluntary decline in fertility rates around the world through promoting what nearly everyone wants: gender equity and universal access to education and full family planning services. The faster we get to negative population growth, the better. You can help by supporting the Global HER (Health, Empowerment and Rights) Act, H.R. 556, as a way to end the Global Gag Rule that’s obstructing family planning services around the world.
We could make a real difference now simply by preventing many of the world’s 32 million unintended births per year. 1.3 million of these are in the U.S., where a child will have much, much greater Anthropocene impact than a child born nearly anywhere else.
Carrying capacity, whatever it might be, is perhaps best measured not by counting some idealized number of humans, but by first understanding and restoring the natural world that has fostered our harmful growth. If we’re able to stabilize and then begin reducing world population in the coming decades, we should do so with an eye toward what constitutes a lush, diverse Earth. If we know those parameters, then we’ll know something about our limits. A good place to start is the Nine Planetary Boundaries from the Stockholm Resilience Centre, but that’s a complex story for another day.
As are the many other population questions I plan on addressing sometime, like whether reducing consumption and inequality are more important than reducing population, or how the economics of negative growth might work. For now, though, let’s just count ourselves lucky to be here at all. In my case, I’m lucky enough to be able to walk by the sea, like Homo antecessor, with our old sweet collie.
