"During the brief time since James Watt's commercial production of the improved Newcomen steam engine in 1775, a revolution unparalleled in human history has occurred at all levels of society and has penetrated all aspects of culture. The technological innovations are, of course, dramatic, but equally important are the biological, political, social, and economic consequences of modernization. From a biological perspective, the most important consequence is the extension of the human life span and the growth in human numbers. In the past two centuries, life expectancy has nearly tripled and the population of our species has multiplied five times over."

"Whether or not such a hypothesis fully accounts for the population increase that accompanies a sedentary life, there can be no doubt that human numbers soared. In the interval from 10,000 to 6000 years ago—a mere 160 human generations—the population of the Near East is estimated to have increased from less than 100,000 people to more than three million. With each increase, additional pressure was placed upon the food producers to domesticate new species and to invent new technologies, such as those based on the plow and on irrigation. Human beings now found themselves on a treadmill from which to this day they have not been able to get off. They are still plagued by the basic paradox of food production: Intensification of production to feed an increased population leads to a still greater increase in population."

"If we discovered tomorrow that there was an asteroid on a collision course with Earth, and—because physics is a fairly simple science—we were able to calculate that it was going to hit Earth on June 3, 2072, and we knew that its impact was going to wipe out 70 percent of all life on Earth, governments worldwide would marshal the entire planet into unprecedented action. Every scientist, engineer, university, and business would be enlisted: half to find a way of stopping it, the other half to find a way for our species to survive and rebuild if the first option were unsuccessful. We are in almost precisely that situation now, except that there isn’t a specific date and there isn’t an asteroid. The problem is us. Why we are not doing more about the situation we’re in—given the scale of the problem and the urgency—I simply cannot understand. We’re spending 8 billion euros (about 11 billion dollars [at the writing's current exchange]) at to discover evidence of a particle called the Higgs-Boson, which may or may not eventually explain the concept of mass and provide a partial thumbs-up for the “standard model” of particle physics. And CERN’s physicists are keen to tell us it is the biggest, most important experiment on Earth. It isn’t. The biggest and most important experiment on Earth is the one we're all conducting, right now, on Earth itself. Only an idiot would deny that there is a limit to how many people our Earth can support. The question is, is it seven billion (our current population), 10 billion or 28 billion? I think we've already gone past it. Well past it. We could change the situation we are now in. Probably not by technologizing our way out of it, but by radically changing our behavior. But there is no sign that this is happening, or about to happen. I think it’s going to be business as usual for us."

"Saying “Don’t have children” is utterly ridiculous. It contradicts every genetically coded piece of information we contain, and (at least in their conception) one of the most important (and fun) impulses we have. That said, the worst thing we can continue to do—globally—is have children at the current rate. Even if a global nuclear power program were set up, even if geoengineering somehow took care of the climate-change problem, and even if we consumed less, we’d still at some point hit a brick wall if the human population continues to grow at anything like its current rate. We all know there’s a link between educating women in the developing world and reducing the birth rate. But despite this, and despite contraception being free in a number of countries where population is increasing, average birth rates are still three, five, or even seven children per woman. According to the United Nations, Zambia’s population is projected to increase by 941 percent by the end of the century. The population of Nigeria is projected to grow by 349 percent—to 730 million people. Afghanistan by 242 percent, The Democratic Republic of Congo by 213 percent, Gambia by 242 percent, Guatemala by 369 percent, Iraq by 344 percent, Kenya by 284 percent, Liberia by 300 percent, Malawi by 741 percent, Mali by 408 percent, Niger by 766 percent, Somalia by 663 percent, Uganda by 396 percent, Yemen by 299 percent. Even the United States is projected to grow by 53 percent by 2100, from 315 million in 2012 to 478 million. I do just want to point out that if the current global rate of reproduction continues, by the end of this century there will not be ten billion of us. There will be twenty-eight billion of us."

"As our numbers continue to grow, we continue to increase our need for far more water, far more food, far more land, far more transportation, and far more energy. As a result, we are now accelerating the rate at which we’re changing our climate. In fact, our activities are not only completely interconnected with, but are now also interacting with, the complex system we live on: Earth. It is important to understand how all this is connected. An increasing population accelerates the demand for more water and more food. Demand for more food increases the need for more land, which accelerates deforestation. Increasing demand for food also increases food processing and transportation. All of these accelerate the demand for more energy. This then accelerates greenhouse gas emissions, principally CO2 and methane, which further accelerate climate change. As climate change accelerates, it increases stress on water, food, and land. And at the same time, an increasing population also accelerates stress on water, food, and land. In short, as population increases, and as economies grow, stress on the entire system accelerates sharply."

"We humans emerged as a species about 200,000 years ago. In geological time, that is really incredibly recent. Just 10,000 years ago, there were one million of us. By 1800, just over 200 years ago, there were 1 billion of us. By 1960, 50 years ago, there were 3 billion of us. There are now over 7 billion of us. By 2050, your children, or your children's children, will be living on a planet with at least 9 billion other people. Some time towards the end of this century, there will be at least 10 billion of us. Possibly more. We got to where we are now through a number of civilization-and society-shaping “events”; most notably, the agricultural revolution, the scientific revolution, and—in the West—the public-health revolution. These events have fundamentally shaped how we live, and have fundamentally shaped our planet. Their legacy will continue to shape our future. So we need to look at our growth and activities through the lens of these developments. One of the principal reasons for this growth was the invention of agriculture. The “agricultural revolution” enabled us to go from being hunter-gatherers to highly organized producers of food, and allowed our population to grow. A useful way to think of the development and importance of agriculture is in terms of at least three agricultural “revolutions.” The first took place over 10,000 years ago. This was the domestication of animals and the cultivation of plant types. The second agricultural revolution was between the fifteenth and nineteenth centuries. This was a revolution in agricultural productivity and the mechanization of food production. The third happened between the 1950s and 2000s; the so-called “green revolution.” But there’s another story here: the start of a fundamental transformation—of land use—by humans."

"Earth is home to millions of species. Just one dominates it. Us. Our cleverness, our inventiveness, and our activities have modified almost every part of our planet. In fact, we are having a profound impact on it. Indeed, our cleverness, our inventiveness, and our activities are now the drivers of every global problem we face. And every one of these problems is accelerating as we continue to grow towards a global population of ten billion. In fact, I believe we can rightly call the situation we're in right now an emergency – an unprecedented planetary emergency."

"The debate regarding which individual factor, among the three key factors producing the environmental crisis, causes more damage - the size of the human population on the planet, excessive consumption of resources, or unequal/ unjust distribution of resources among countries [the wealthier countries consume much more resources, per person on average than poorer countries] - is like a debate about which contributes more to a triangle, the base or the ribs of the triangle. You can not separate the three factors. If we analyze the numbers over a relatively longer time interval, we will conclude that the size of the population has a bigger impact than consumption. On the other hand, consumption and unequal distribution are also important aspects. If we do not change these three factors all at the same time, the quality of our life will change dramatically. Today humanity is delivering a serious blow to [the rest of] nature, but it is clear that nature will deliver the final blow."

"The key to understanding overpopulation is not population density but the numbers of people in an area relative to its resources and the capacity of the environment to sustain human activities; that is, to the area’s carrying capacity. When is an area overpopulated? When its population can’t be maintained without rapidly depleting nonrenewable resources... By this standard, the entire planet and virtually every nation is already vastly overpopulated."

"Part of human impact on the earth relates to our swiftly growing numbers. If we do not take deliberate, conscious action to maintain a reasonable balance between the numbers of people and the environmental wealth required to sustain us, nature will make appropriate adjustments, and famine, disease, and wars-the predictable outcomes of living beyond one's environmental means, of overspending environmental capital-will ultimately force a cruel discipline."

"The population boom of the last few centuries […] was made possible by massive advances in living standards, economic growth, surpluses of food, and vastly improved public health. All of this, however, was sustained by fossil fuels. Once fossil fuel reserves peak […] production, growth, and the amenities of modern life will gradually halt. Contemporary industrial society will downgrade into a “scarcity society” that manages on minimal energy, after which it will become a “salvage society” that scrapes survival from the refuse of the defunct urban buildings, information networks, and industrial centers."

"The situation in which we find ourselves today is unique as regards the magnitude and rate of growth of the human enterprise. The turn now being taken by the vicious circle is tremendous. […] The mastery of fire, one of humans' first instances of technological development, continues to be of paramount importance today with the burning of fossil fuels. And so the vicious circle of the development of humankind churns on, and does so with ever greater momentum due to the constantly increasing consumption of fossil fuels and metals, with only the tiniest sign of resistance in the form of the efforts of environmental organisations and green political parties."

"Environmental analysts regard a sustainable human population as one enjoying a modest, equitable middle-class standard of living on a planet retaining its biodiversity and with climate-related adversities minimized. Analysts' estimate[s] of that population size vary between 2 and 4 billion people, a figure obviously well below the present 7.9."

"Our use of energy has been increasing ever since we discovered and mastered fire and developed agriculture, but mostly since we gained access to a vastly increased energy supply by extracting millions of years of stored and concentrated solar energy from the Earth’s crust in the form of fossil fuels. Combined with the development of new energy conversion techniques, this energy bonanza made it possible to lift the secular barriers to human population and output growth. The new energy sources, forms and uses that came online since the turn of the 19th century gave us access to more materials and enabled the invention of new and increasingly sophisticated exosomatic instruments (i.e. machines), which in turn made it possible to access ever more energy and matter and to transform them ever more effectively and efficiently. This resulted in a rapid rise in our total energy and material “throughput” (i.e. the flow of raw materials and energy from the biosphere’s sources, through the human ecosystem, and back to the biosphere’s sinks), which is what we commonly measure through the proxy concept of “economic growth”. This rise never stopped since then, even if the global distribution of the flows of energy and material inputs, outputs and wastes evolved over time. Our efforts to increase the “energy efficiency” of our machines and processes (i.e. reducing the amount of energy needed to perform certain tasks) never resulted in a reduction of the total energy we used, but on the contrary only contributed to create more room for increasing the rate of our consumption."

"Over the last century the pace of many human activities has so accelerated, and human overpopulation grown so severe, to have created a dramatic global environmental transformation. Most natural ecosystem have been highly modified or have disappeared altogether, and the abundance of wildlife has been greatly reduced."

"We are in the sixth mass extinction event. Unlike the previous five, this one is caused by the overgrowth of a single species, Homo sapiens."

"Life has now entered a . This is probably the most serious environmental problem, because the loss of a species is permanent, each of them playing a greater or lesser role in the living systems on which we all depend. The species extinctions that define the current crisis are, in turn, based on the massive disappearance of their component populations, mostly since the 1800s. The massive losses that we are experiencing are being caused, directly or indirectly, by the activities of Homo sapiens. They have almost all occurred since our ancestors developed agriculture, some 11,000 y ago. At that time, we numbered about 1 million people worldwide; now there are 7.7 billion of us, and our numbers are still rapidly growing. As our numbers have grown, humanity has come to pose an unprecedented threat to the vast majority of its living companions."

"We need to realize the "load" with which we humans burden the planet's ecosystems consists of more than just a population number. People living by different cultures not only reproduce at different rates; they impose very different per capita ecological impacts. Culture includes a population's technology and people's ways of organizing themselves. Each of us living in a "developed" country (i.e., industrialized far beyond anything conceivable to Malthus) has an enormously greater resource appetite and environmental impact than does each resident of a so-called "developing" country. For our grossly unsustainable manner of living, 6 billion is far too many."

"[Hu]man[s]... have imagined... [themselves] to be more unlike other mammals than [t]he[y] really... [are], so when human behavior has shown these same characteristics, various other explanations have been put forth which have obscured the significance of population pressure itself. In the twentieth century, with human numbers enlarged and resource drawdown becoming significant, [hu]man[kind] went to war. [T]he[y] rioted in the streets. [T]he[y] committed more... crimes of violence. [...] [Their] political attitudes polarized and [t]he[y] created totalitarian governments, some of which gave license to sadistic tendencies. A generation gap widened and deepened. In spite of earnest efforts by humane activists to inhibit racism and to rectify economic inequality, disparities between people remained and animosities became more virulent. Standards of decency in behavior toward others and expectations of considerate self-restraint were eroded and degraded in many places."

"People displayed either persistent ignorance of the carrying capacity concept or naive faith that carrying capacity could always be expanded, [and] that limits could always be transcended. Such an assumption seemed to underlie the stubborn refusal of capitalists and Marxists alike to acknowledge that the myth of limitlessness had, at last, become obsolete. There was also the assumption that further advances in technology would necessarily enlarge carrying capacity, not reduce it. Enlargement of carrying capacity had been the role of technology in the past; however… there has been a reversal of this role in the industrial era. Technology has enlarged human appetites for natural resources, thus diminishing the number of us that a given environment can support."

"Scarcely more than two generations had tasted the fruits of industrialization when the growth of population was still further accelerated by truly effective death control. The role of microorganisms in producing diseases was discovered. In 1865 the practice of antiseptic surgery began. It serves... as a reasonable demarcation of the beginning of an era filled with related breakthroughs in medical technology: hygienic practices, vaccination, antibiotics, etc. The total effect of this recent series of achievements has been to emancipate mankind more... from the life-curtailing effects of the invisible creatures for which human tissues used to serve as sustenance. Like other prey species newly protected from their predators, we have been fruitful and have so multiplied that we have much more than "replenished" the earth with our kind."

"We are already living on an overloaded world. Our future will be a product of that fact; that fact is a product of our past. Our first order of business, then, is to make clear to ourselves how we got where we are and why our present situation entails a certain kind of future. […] It is the story of a world that has again and again approached the condition of being saturated with human inhabitants, only to have the limit raised by human ingenuity. The first several rounds of limit-raising were accomplished by a series of technological breakthroughs that took almost two million years. These breakthroughs enabled human populations repeatedly to take over for human use portions of the earth’s total life-supporting capacity that had previously supported other species. The most recent episode of limit-raising has had much more spectacular results, although it enlarged human carrying capacity by a fundamentally different method: the drawing down of finite reservoirs of materials that do not replace themselves within any human time frame. Thus its results cannot be permanent. This fact puts mankind out on a limb which the activities of modern life are busily sawing off."

"Today [hu]mankind is locked into stealing ravenously from the future. Famine in the modern world must be… one of several symptoms reflecting a deeper malady of in the human condition—namely, diachronic competition, a relationship whereby contemporary well-being is achieved at the expense of our descendants. By our sheer numbers, by the state of our technological development, and by being oblivious to differences between a method that achieved lasting increments of human carrying capacity [agriculture] and one that achieves only temporary supplements [reliance on fossil fuels and other mined substances], we have made satisfaction of today's human aspirations dependent upon massive deprivation for posterity."

"Thomas Malthus, an eighteenth-century economist, once predicted that because our population size increases exponentially while our food supply increases arithmetically, our population will one day exceed our ability to sustain it. While this has now been disproven with the creation of processed foods and genetically modified organisms, [Peter] Farb’s paradox may hold true. Because Earth’s population is growing, we increase our food production. Then, because we have a surplus of food, people are more well-nourished, leading to higher life expectancies and lower infant mortality rates, and people are able to have more children. This cyclical paradox is not healthy for our planet because while we may be able to sustain our growing population’s appetites, our other important resources, such as water and oil, are dwindling. To have a sustainable population size, we should be reproducing at a replacement rate, much like Denmark and Japan are."

"During the past hundred years, Homo sapiens population increased from 2 billion to nearly 8 billion and the United Nations (2019) projects an increase of 3 billion more by 2100, unless steps are taken to reduce this population growth. Ignoring this projected increase means ignoring a major driver of the unfolding biodiversity crisis; accepting current bloated human numbers as an appropriate status quo means accepting a biologically impoverished planet."

"Global biodiversity decline is best understood as too many people consuming and producing too much and displacing other species. Wild landscapes and seascapes are replaced with people, our domestics and commensals, our economic support systems, and our trash."

"All living species must take from nature to survive, and we are no different. But unlike other species, there seems to be no end to our quest for food, comfort, shelter, sex — the fundamental necessities of survival that are now pursued in overdrive, far beyond our existential needs. We are compelled to progress, and have extracted resources from the land since we first stood on two feet. The entire twentieth century has been a revving up of this large consumptive engine, and this insatiable human striving has assaulted the very planet that sustains us. In a very short period of time, humankind, with its population explosion, industry and technology, has become an agent of immense global change. What this civilization leaves in the wake of its progress may be an opened and emptied Earth. But in performing these incursions, we also participate in the unwitting creation of gigantic monuments to our way of life."

"It seems self-evident that our fundamental predicament of ecological overshoot is a direct result of humanity’s growth with too many people consuming too many resources and producing too many waste products for a finite planet dependent upon healthy ecological systems. And while this doesn’t require much explanation for those who acknowledge that we live upon a world with finite resources and limited capacity to compensate for our waste production, there are still many who believe that Homo sapiens’ rather unique cognitive abilities and technological prowess can and will ‘solve’ the many challenges we appear to be encountering as we reach and surpass the planetary limits of our relatively recent explosive growth, global expansion, and industrialisation."

"... Reverend THOMAS MALTHUS' prediction made in 1798—that man would reproduce himself into a condition of "misery and vice" because of the growing imbalance caused by the multiplication of his own numbers by geometric progression, while his food supply was increasing arithmetically—is as valid today as when it was made. He was a visionary and saw clearly the monster of overpopulation. The only error in his prediction was one of a "few seconds on the clock of human occupancy of the earth". We, agriculturists, can buy at most a few decades of time in which to bring population growth into successful balance with food production."

"In my opinion, you have out-of-control population growth, and you have fewer and fewer [resources]—we are heading for the biggest train wreck our civilization has ever come across ever. Ever. And I think that within 40 or 50 years, we’ll be there. If your population curve is on an exponential growth, and the resources are on an exponential decline, what happens first is you get increases in wealth discrepancy, which means that you get rich pockets of gated communities with security guards outside them, and you get more and more poverty outside that area. And the resources go down, and people start having resource wars over water and food and agriculture and arable land, and then you have Joburg in 2050. And you can see signs of it everywhere. It’s just overpopulation and lack of resources. We just aren’t in control of our destiny."

"Currently, the operation of our present industrial civilization is almost wholly dependent on access to huge amounts of fossil fuels. It is important to understand that fossil fuels, especially oil, are not simply used to manufacture and propel passenger automobiles or trucks. They also facilitate the mass assembly of tractors, plows, irrigation pipes, and pumps and then turn around and power them also. They constitute the chemical base of many crucial fertilizers and pesticides. They are also the building blocks of agricultural plastics. They refrigerate perishables. In short, the modern industrial agriculture system could not function without copious amounts of fossil fuel. In the absence of fossil fuel-based industrial agriculture, world food production would plummet to a scale completely inadequate to sustain our current population size, let alone the net addition of over 80 million more people each year. The other side of the coin is that when humans co-opt the extraordinary power found in fossil fuels, we become “overpowered” – and that is how we are over-powering the Earth’s biosphere. We cannot destroy rainforests at the rate of several football fields per minute, trawl the deep oceans, attempt mass-scale aqua-culture, fragment habitat with asphalt roads, or construct miles and miles of urban sprawl without the power of fossil fuels. In summary, fossil fuels underwritten both our population size and growth and our discretionary (over)consumption."

"The geometric growth rate of humans is unprecedented and never in the history of the earth has a single species grown to such bloated proportions, completely out of balance with living systems. The problem is only worsening. On conservative estimates, the human population is expected to swell upwards to 8–10 billion by 2050, and perhaps expand significantly by 2100. Human population growth represents a crisis of the highest order, but of course, it is only one aspect of multiple crises -- including species extinction and climate change -- merging together in a perfect storm of catastrophe that forms the daunting challenges facing humanity in the Anthropocene."

"Whereas the unconscious operations and blind forces of the planet have provoked turbulent changes over the last 4.5 billion years of earth’s evolutionary history, now change is being directed by a conscious and volitional agent – "humanity." We cannot speak of humanity equally, to be sure, as the problem was caused by the industrialized capitalist West and the poorer nations who contributed least to climate crisis will be hit the hardest. But nations such as China, India, and Brazil are major contributors, and the cumulative impact of 7.5 billion people on the planet is causing extinction and collapse everywhere. The stability of the Holocene is now gone, changes are accelerating beyond our understanding and control, and chaos waits at our door."

"As we slide seamlessly from 7 billion to 8 billion humans, each generation more powerful, polluting, and destructive than the previous, I have to wonder whether one century is too much time to allow a “natural” progression into negative population growth, or whether the biodiversity damage a century like this one will inflict could be incalculable and irreversible, if not terminal for us. Think about the honey bees and hummingbirds. Think about the sudden absence of insects we are seeing all over the world, and how that soon may affect populations farther up or down the food chain. Now, Mr. Biotech Billionaire, are you serious about populating the world with thousands or millions of bicentiniarians [sic] and tricentinarians [sic]?"

"The success of modern medicine is today so great, that millions of people are kept alive - if not cured - who in earlier days, and with less scientific aptitude, would normally have died. In this developed skill and knowledge, and in this aptitude in the care of the physical mechanism, is today to be found a major world problem - the problem of overpopulation of the planet, leading to the herd life of humanity and the consequent economic problem - to mention only one of the incidental difficulties of this success. This "unnatural" preservation of life is the cause of much suffering, and is a fruitful source of war, being contrary to the karmic intent of the planetary Logos. With this vast problem, I cannot here deal. I can only indicate it. It will be solved when the fear of death disappears, and when humanity learns the significance of time and the meaning of the cycles."

"We are a plague on the Earth. It’s coming home to roost over the next 50 years or so. It’s not just climate change; it’s sheer space, places to grow food for this enormous horde. Either we limit our population growth, or the natural world will do it for us, and the natural world is doing it for us right now."

"It's going to destroy it all. I use what I call my bathroom metaphor. If two people live in an apartment, and there are two bathrooms, then both have what I call freedom of the bathroom, go to the bathroom any time you want, and stay as long as you want to for whatever you need. And this to my way is ideal. And everyone believes in the freedom of the bathroom. It should be right there in the Constitution. But if you have 20 people in the apartment and two bathrooms, no matter how much every person believes in freedom of the bathroom, there is no such thing. You have to set up, you have to set up times for each person, you have to bang at the door, aren't you through yet, and so on. And in the same way, democracy cannot survive overpopulation. Human dignity cannot survive it. Convenience and decency cannot survive it. As you put more and more people onto the world, the value of life not only declines, but it disappears. It doesn't matter if someone dies."

"Babies are the enemies of the human race... Let's consider it this way: by the time the world doubles its population, the amount of energy we will be using will be increased sevenfold which means probably the amount of pollution that we are producing will also be increased sevenfold. If we are now threatened by pollution at the present rate, how will we be threatened with sevenfold pollution… distributed among twice the population? We'll be having to grow twice the food out of soil that is being poisoned at seven times the rate."