Our planet is home to an incredible diversity of organisms. What does the earth’s biodiversity look like in the big picture?
In this post I provide an overview – with summary graphic – of Earth’s biomass, how it is distributed between taxa (the taxonomic group of organisms), and the environments within which they live. This summary is based on the findings of research by Bar-On, Phillips & Milo published in the Proceedings of the National Academy of Sciences (PNAS).1
There are several ways we can answer the question of how much life is on Earth. We could, for example, count the number of species, population sizes or the number of individual organisms. But these metrics can make it difficult to compare between taxa: small organisms may have a large population but still account for a very small percentage of Earth’s organic matter.
For a meaningful comparison, Bar-On et al. (2018) quantified life using the metric of biomass. Biomass is measured here in tonnes of carbon as it is a key building-block of life.2
In the graphic below I summarize the distribution of global biomass by taxonomic kingdom (on the left), with a magnified snapshot of the animal kingdom (on the right).
What are the stand-out points?
- plants – mainly trees – dominate life on Earth: they account for more than 82% of biomass;
- surprisingly in second place is the life we cannot see: tiny bacteria sum up to 13%;
- whilst our perceptions are often focused on the animal kingdom, it accounts for only 0.4%;
- humans account for just 0.01% of biomass, so we’d need about 70 trillion of us to match Earth’s collective biomass.3
[Clicking on the visualization below will open it in higher-resolution].
Humans comprise a very small share of life on Earth — 0.01% of the total, and 2.5% of animal biomass [animal biomass is shown in the right-hand box on the visualization above].
But we are also responsible for the animals we raise. Humans alone may seem insignificant, but our hunger for raising livestock means we have played a major role in shifting the balance of animal life: livestock account for 4% of animal biomass.4
Livestock accounts for more biomass than all humans on earth; more than 50% greater than humans.
And livestock accounts for much more than all wildlife: Wild mammals and birds collectively account for only 0.38% — livestock therefore outweighs wild mammals and birds by a factor of ten.5
Carrying Capacity – World Population
No species has altered the Earth’s natural landscape the way humans have. Our impact is so extensive that we are crossing into a new geologic epoch – the Anthropocene – propelled by human behavior.
Global climate change, mass extinction, and overexploitation of our global commons are all examples of the ways in which humans have altered the natural landscape. Our growing population, coupled with rising affluence and per capita impact, is driving our planet closer to its tipping point.
With population expected to reach 9.5 billion by 2050, many wonder if our natural resources can keep up with our growing demands.
The World Population Map can be viewed with the data overlay, “Anthropogenic Transformation,” created by ecologist Erle Ellis.
Instead of dividing the world into classical biomes (savanna, rainforest, woodlands, tundra, etc.
), Ellis conceived of depicting a map of “anthromes” to describe the way human have reshaped the earth’s ecological patterns. The Anthrome map shows croplands, rangelands, urban areas and other human settlements.
Understanding Carrying Capacity
Human population, now over 7 billion, cannot continue to grow indefinitely. There are limits to the life-sustaining resources earth can provide us. In other words, there is a carrying capacity for human life on our planet. Carrying capacity is the maximum number of a species an environment can support indefinitely.
Every species has a carrying capacity, even humans. However, it is very difficult for ecologists to calculate human carrying capacity. Humans are a complex species. We do not reproduce, consume resources, and interact with our living environment uniformly.
Carrying capacity estimates involve making predictions about future trends in demography, resource availability, technological advances and economic development.
Our Ecological Footprint
One way to address the challenges associated with making future projections is to look at current human impact on the planet. The ecological footprint is a measurement of the anthropogenic impact on earth.
It tracks how much biocapacity (biological capacity) there is and how much biocapacity people use by comparing the rate at which we consume natural resources and generate waste to the planet’s ability to replenish those resources and absorb waste. Today, our global footprint is in overshoot. It would take 1.
5 Earths to sustain our current population. If current trends continue, we will reach 3 Earths by the year 2050.
Where Do We Grow From Here?
Our planet does not have the biocapacity to sustain our current levels of growth and resource consumption.
So, what can be done to minimize our collective impact on the environment? In his book, How Many People Can the Earth Support?, mathematical biologist Joel Cohen classifies current solutions into three paradigms: those looking for a “bigger pie” (improving technology), those advocating for “fewer forks” (slowing population growth), and those looking to rationalize and improve decision-making though “better manners” (changing global culture). Cohen argues that, standing along, each paradigm is necessary in solving our environmental crisis, but not sufficient. Change must come from a combination of all three. “Promoting access to contraceptives, developing economies, saving children, empowering women, educating men, and doing it all at once,” he writes, is a way to both lower our impact on the planet and improve the quality of life for all. Perhaps Oxford economist Robert Cassen said it best, “Virtually everything that needs doing from a population perspective needs doing anyway”. Adopting human-centered initiatives targeted at addressing both population growth and consumption habits, ranging from the individual to trans-national level, are our best hope for achieving a sustainable future.
Human Population 1 CE – 2050 CE
How Many Animals Are There in the World?
Today’s Wonder of the Day was inspired by helaina from clearwater, FL. helaina Wonders, “How many animals are on earth?” Thanks for WONDERing with us, helaina !
We were hiking through the Wonderopolis jungle the other day on our way to the beach when we stopped to take a break under a big shade tree. We were about to close our eyes for a short siesta when we overheard a monkey and a sloth having an interesting conversation in the branches above us:
Monkey: Hey Sloth! Wake up! Did you know you can see all the way to the beach from up here?
Sloth: I'm awake, Monkey. Wow! Look at all the humans on the beach. What are they doing?
Monkey: They call it sunbathing. I don't get it. They just lie there on the sand and sweat.
Sloth: Why would they do that when they could nap in a nice, cool tree?
Monkey: They would need a lot of trees. Look at all of them! How many are there? Help me count. 1…2…3…4…no, wait, did I already count that one?
We couldn't nap with those two chattering above us, so we moved on down the path. Their conversation did make us WONDER about population, though. We already have an idea of how many humans there are on Earth, but we were curious about how many animals of all kinds there are in the world.
Unfortunately, that question doesn't have an easy answer. Scientists who have tried to answer it have only been able to come up with rough estimates that have a wide margin of error.
If you want to understand how difficult it is to get an accurate count of all the animals in the world, we have a challenge for you: count all the animals on the property you call home. This would include your house and the land that it sits on.
Start with the humans in your home. They're easy to count. If you have pets, those are easy to count, too. But there are so many more animals around you. Don't forget the birds and squirrels living outside your home. You also need to count the rabbits, raccoons, mice, and other creatures not easily seen during the day.
If you have a pond on your property, don't forget to count the fish! Finally, you must be sure to count the most populous group of animals in any area: insects. That means you need to count every ant, fly, and mosquito.
If you give this challenge a serious try, you will soon understand the problem that scientists who have considered this question face. There are simply so many animals to count and many of them are nearly impossible to track down or keep track of.
Some are too small to see, and others are in places too difficult to reach. There are even too many humans spread too far around the globe to ever know with precision exactly how many humans are on Earth at any particular time. That's why scientists tend to rely upon estimates to make educated guesses about populations.
Let's take a look at a few facts and figures that highlight the problem of trying to estimate how many animals there are in the world. First, we don't even know how many types of animals there are in the world, let alone how many individual animals there are.
Scientists have recently estimated that there are approximately 8.7 million species on Earth. They believe that 1-2 million of those species are animals. And what do we know about all those species? Not much! The same study estimates that 86% of all land species and 91% of all sea species have not yet been discovered or described!
Sticking to the species we do know about, let's look at some amazing numbers for particular groups of animals. Scientists believe there are over seven billion humans in the world today. That's a staggering number, but there are more chickens (over 18 billion) than humans. At least we humans do outnumber cattle (1.4 billion) and sheep (1.1 billion).
Those numbers pale in comparison to the insect world, though. For example, scientists estimate there are over 10,000 trillion ants alive at any one time.
Based upon those numbers, some scientists estimate the total insect population at 10 quintillion, which is 10 billion billion! That figure has led at least one expert to estimate the total animal population on Earth to be about 20 quintillion, or 20 billion billion!
What Was It Like When The First Humans Arose On Earth?
70,000 years ago, a brown dwarf pair known as Scholz's Star, right on the precipice of igniting… [+] hydrogen fusion in its core, passed through the Solar System's Oort cloud. Stars, failed stars, and stellar remnants pass through our Solar System multiple times every million years. Both modern humans and Neanderthals were likely around to see this event.
José A. Peñas/SINC
By the time our planet was four billion years old, the rise of large plants and animals was just beginning.
Complexity exploded around that time, as the combination of multicellularity, sexual reproduction, and other genetic advances brought about the Cambrian explosion.
Many evolutionary changes occurred over the next 500 million years, with extinction events and selection pressures paving the way for new forms of life to arise and develop.
65 million years ago, a catastrophic asteroid strike wiped out not only the dinosaurs, but practically every animal weighing over 25 kg (excepting leatherback sea turtles and some crocodiles).
This was Earth's most recent great mass extinction, and left a large number of niches unfilled in its wake. Mammals rose to prominence in the aftermath, with the first humans arising less than 1 million years ago.
Here's our story.
A planetoid colliding with Earth, analogous to (but larger and slower-moving) a potential impact… [+] between Swift-Tuttle and Earth. The asteroid that wiped out the dinosaurs had just 1/26th the energy that being hit by Comet Swift-Tuttle would carry, and that impact was enough to wipe out 75% of all species on Earth.
NASA / Don Davis
65 million years ago, a massive asteroid somewhere between 5 and 10 kilometers in diameter struck our planet. It kicked up a layer of dust that settled all over the world, a layer that can be found today in our planet's sedimentary rock.
On the older side of that layer, fossils such as dinosaurs, pterosaurs, ichthyosaurs and plesiosaurs are abundant.
Giant reptiles, ammonites, and large classes of plants and animals all existed prior to that event, along with small, flying birds and the tiny, land-dwelling mammals.
After that event, the mammals survived. With no larger predators to stop them, they grew, diversified, and experienced a population explosion. Primates, rodents, lagomorphs, and other forms of mammals, including placental mammals, marsupials, and even the egg-laying mammals are all abundant at the start of the Cenezoic epoch.
A duck-billed platypus (Ornithorhynchus anatinus) swims in the Tyenna River in Mt. Field National… [+] Park, Tasmania. Despite the fact that it lays eggs, has a bill, and has a myriad of features we don't typically associate with mammals, the duck-billed platypus is more closely related to us than it is to any extant bird or reptile.
Almost immediately, the primates began diversifying even further. 63 million years ago — just 2 million years after the demise of the dinosaurs — they split into two groups.
- The dry-nosed primates, known formally as the haplorrhines, which developed into modern monkeys and apes.
- The wet-nosed primates, known as the strepsirrhines, which developed into modern lemurs and aye-ayes.
58 million years ago, another big change occurred: the haplorrhines experienced an interesting genetic split, as the first novel and unique evolutionary branch became distinct from the rest of the dry-nosed primates: the tarsier. With its enormous eyes, it was uniquely well-adapted to see at night.
With its enormous eyes but a dry nose, the tarsier holds the distinction as the first haplorrhine to… [+] diverge from the mammalian lineage that would give rise to monkeys, apes, and eventually modern humans. Note that they have dry, rather than wet, noses.
The niche it now occupied was sufficiently different from the remaining groups of our ancestors that they evolved differently from the rest of their cousins from this point onwards. This type of evolutionary splitting occurs every so often, and isn't unique to primates.
Although we normally don't think very much about our distant cousins and how they develop once they've split off from us, it isn't just haplorrhines like us (and our direct ancestors) that underwent interesting phases of evolution.
All throughout the past 65 million years — just as it was before that time — the various mammals, birds, plants, and other living organisms evolved together.
Evolution is driven by environmental changes, and that includes all the floral and faunal changes that occur on our planet.
A reconstructed illustration of the protocetid Georgiacetus vogtlensis, a primitive whale-like… [+] creature dating from the Eocene period.
Nobu Tamura / cc-by-sa-3.0
55 million years ago, a sudden rise in greenhouse gases causes the global average temperature to swiftly rise, wiping out many deep-ocean animals and plants. This transformation left many large, unfilled niches in the ocean, paving the way for cetaceans (the large oceanic mammals) to develop.
50 million years ago, some of the even-toed mammals begin evolving into sea-dwelling creatures. The artiodactyls may have all evolved from a single, common ancestor, or may have evolved independently. Animals like Indohyus, which dates to 48 million years ago, may have given rise to protocetids: shallow-water mammals that returned to land to give birth.
The early fossilized remains of Darwinius Masilae, known as “Ida,” was originally thought by many to… [+] be a missing link in human ancestry, but this specimen is almost certainly a strepsirrhene, not a haplorrhine like monkeys, apes, and humans are. Although it dates back to 47 million years ago, it is probably more closely related to a lemur than it is to a human.
Nachosan / Wikimedia Commons
Right around that time, 47 million years ago, the primate Darwinius masillae existed, as the fossil Ida, preserved from that time, provides a spectacular example. Although this was originally touted as a proverbial “missing link” in human evolution, Ida is not a haplorrhine like us, but a strepsirrhene: a wet-nosed primate.
But another 7 million years later — 40 million years ago — an important development occurred among the dry-nosed primates: the New World monkeys branched off.
Humans and our ape ancestors are descended from Old World monkeys; New World monkeys are the first simians (or higher primates) to evolutionary diverge from our lineage.
They would go on to colonize most of South America, where they are still found in abundance today.
The golden-headed lion tamarin is an example of a New World monkey. This endangered species of… [+] animal is part of a lineage that split off from the Old World monkeys that humans are a part of some 40 million years ago.
The Old World monkeys continue to thrive and successfully occupy their niches, while diversifying in body size and physical features.
25 million years ago, the first apes arise, splitting off from the remaining Old World monkeys at this time.
The apes — defined by the complete lack of a tail of any type — would go on to give rise to many of the close relatives of humans that survive today: both the lesser apes and the great apes.
The earliest ape to split off from the Old World monkeys was the Gibbon, a lesser ape that first arose 18 million years ago.
Sometime between 14 and 16 million years ago, the first great apes arose, with Orang-utans branching off 14 million years ago. The Orang-utans spread into southern Asia after this, while the other great apes remained in Africa. The largest primate ever, Gigantopithecus, first arose some 9 million years ago, only becoming extinct a few hundred thousand years ago.
The Orang-utans are some of the earliest great apes to split off from our hominid ancestors, which… [+] they did some 16 million years ago. Although they are true great apes like we are, having no tails, they are less closely related to us than gorillas, bonobos, chimpanzees, or any of the later-emerging members of the family hominidae.
7 million years ago, gorillas branched off from the other great apes; they remain the largest of all the surviving primates.
The great apes split off in two directions 6 million years ago, with one direction giving rise to humanity's ancestors and the other branch giving rise to chimpanzees and bonobos. The chimpanzee/bonobo branch remains unified for another 4 million years, with our closest surviving relatives — the chimpanzees and bonobos — diverging from one another a mere 2 million years ago.
Bonobos, along with chimpanzees, are the two species most closely related to human beings that… [+] remain on Earth today. Bonobos are incredibly social, but still are not truly bipedal, as they maneuver on four limbs frequently. An evolutionary split that occurred approximately 5.6 million years ago marks the divergence of these creatures from modern humans.
But along the track of our direct ancestors, the developments were rapid and profound. 5.6 million years ago, the first truly bipedal ape, Ardipithecus, arose. Although it's a controversial claim, the hand bones in Ardipithecus show evidence of it being a transitional fossil between the earlier great apes and the later Australopithecines.
Approximately 4 million years ago, the first Australopithecus evolved: the first members of the Hominina subtribe (a taxonomic classification more specific than family but less specific than genus). Shortly thereafter, the first evidence of stone tool use appears: presently at 3.4-to-3.7 million years ago.
The human population is 7.5 billion and counting — a mathematician counts how many humans the Earth can actually support
World population numbers are projected to reach 8 billion around 2023 and expected to level off around 10 to 12 billion by 2100. Thomas Peter/Reuters
- The world's population has reached the vicinity of 7.5 to 7.6 billion people.
- Since 1960, world population has grown exponentially by about one billion every 13 years.
- Humans have a large ecological footprint — we are the most populous mammal on Earth today.
- But the Earth will only have capacity for the population to a point until premature death by starvation and disease balances the birth rate.
- World Health Organization figures show 2.1 billion people lack access to safe drinking water, and 4.5 billion lack managed sanitation.
Humans are the most populous large mammal on Earth today, and probably in all of geological history. This World Population Day, humans number in the vicinity of 7.5 to 7.6 billion individuals.
Can the Earth support this many people indefinitely? What will happen if we do nothing to manage future population growth and total resource use? These complex questions are ecological, political, ethical — and urgent. Simple mathematics shows why, shedding light on our species' ecological footprint.
The mathematics of population growth
In an environment with unlimited natural resources, population size grows exponentially. One characteristic feature of exponential growth is the time a population takes to double in size.
Chart: The Conversation/Source: United Nations
Exponential growth tends to start slowly, sneaking up before ballooning in just a few doublings.
To illustrate, suppose Jeff Bezos agreed to give you one penny on Jan. 1, 2019, two pennies on Feb. 1, four on March 1, and so forth, with the payment doubling each month. How long would his $100 billion fortune uphold the contract? Take a moment to ponder and guess.
After one year, or 12 payments, your total contract receipts come to $40.95, equivalent to a night at the movies. After two years, $167,772.15 — substantial, but paltry to a billionaire. After three years, $687,194,767.35, or about one week of Bezos' 2017 income.
The 43rd payment, on July 1, 2022, just short of $88 billion and equal to all the preceding payments together (plus one penny), breaks the bank.
Real population growth
For real populations, doubling time is not constant. Humans reached 1 billion around 1800, a doubling time of about 300 years; 2 billion in 1927, a doubling time of 127 years; and 4 billion in 1974, a doubling time of 47 years.
- On the other hand, world numbers are projected to reach 8 billion around 2023, a doubling time of 49 years, and barring the unforeseen, expected to level off around 10 to 12 billion by 2100.
- This anticipated leveling off signals a harsh biological reality: Human population is being curtailed by the Earth's carrying capacity, the population at which premature death by starvation and disease balances the birth rate.
Chart:The Conversation/Source: United Nations
In 2010, the US used 355 billion gallons of freshwater, over 1,000 gallons per person per day. Nguyen Huy Kham/Reuters
Humans are consuming and polluting resources — aquifers and ice caps, fertile soil, forests, fisheries and oceans — accumulated over geological time, tens of thousands of years or longer.
How many people can our planet really support?
Overpopulation. It is a word that makes politicians wince, and is often described as the “elephant in the room” in discussions about the future of the planet.
You often hear people citing overpopulation as the single biggest threat to the Earth. But can we really single out population growth in this way? Are there really too many people on our planet?
It is clear to all of us that the planet is not expanding. There is only so much space on Earth, not to mention only so many resources – food, water and energy – that can support a human population. So a growing human population must pose some kind of a threat to the wellbeing of planet Earth, mustn't it?
“It is not the number of people on the planet that is the issue – but the number of consumers and the scale and nature of their consumption,” says David Satterthwaite, a senior fellow at the International Institute for Environment and Development in London. He quotes Gandhi: “The world has enough for everyone's need, but not enough for everyone's greed.”
The global impact of adding several billion people to these urban centres might be surprisingly small
The number of “modern human beings” (Homo sapiens) on Earth has been comparatively small until very recently. Just 10,000 years ago there might have been no more than a few million people on the planet. The one billion mark was not passed until the early 1800s; the two billion mark not until the 1920s.
As it stands now, though, the world's population is over 7.3 billion. According to United Nations predictions it could reach 9.7 billion people by 2050, and over 11 billion by 2100.
Population growth has been so rapid that there is no real precedent we can turn to for clues about the possible consequences. In other words, while the planet might hold over 11 billion people by the end of the century, our current level of knowledge does not allow us to predict whether such a large population is sustainable, simply because it has never happened before.
We can get clues, though, by considering where population growth is expected to be strongest in the years ahead. Satterthwaite says that most of the growth over the next two decades is predicted to be in urban centres in what are currently low and middle-income countries.
It is not the number of people on the planet that is the issue – but the number of consumers and the scale and nature of their consumption
On the face of it, the global impact of adding several billion people to these urban centres might be surprisingly small. This is because urbanites in low- and middle-income countries have historically consumed little.
The emissions of carbon dioxide and other greenhouse gases give us a good indication of how high consumption is in a city.
“We know of cities in low-income nations that emit less than one tonne CO2-equivalent per person per year,” says Satterthwaite. “Cities in high-income nations [can] have six to 30 tonnes CO2-equivalent per person per year.”
Citizens of more affluent nations leave a much greater footprint on our planet than people living in poorer countries – although there are exceptions. Copenhagen is the capital of a high-income nation – Denmark – while Porto Alegre is in upper-middle-income Brazil. Living standards are high in both cities, yet per capita emissions are relatively low.
Satterthwaite goes on to say that if we look at an individual's lifestyle, the differences between wealthy and non-wealthy groups are even more dramatic. There are many low-income urban dwellers whose consumption is so low that they contribute almost nothing to greenhouse gas emissions.
People living in high-income nations must play their part if the world is to sustain a large human population
So a world with a human population of 11 billion might put comparatively little extra strain on our planet's resources. But the world is changing. Low-income urban centres may not continue on low-carbon development trajectories.
The real concern would be if the people living in these areas decided to demand the lifestyles and consumption rates currently considered normal in high-income nations; something many would argue is only fair. If they do, the impact of urban population growth could be much larger.
This fits with a general pattern that has played out over the past century or so, explains Will Steffen, an emeritus professor with the Fenner School of Environment and Society at the Australian National University. It is not the rise in population by itself that is the problem, but rather the even more rapid rise in global consumption (which of course is unevenly distributed).
This leads to an uncomfortable implication: people living in high-income nations must play their part if the world is to sustain a large human population. Only when wealthier groups are prepared to adopt low-carbon lifestyles, and to permit their governments to support such a seemingly unpopular move, will we reduce the pressure on global climate, resource and waste issues.
A 2015 study in the Journal of Industrial Ecology looked at environmental impact from a household perspective. It puts consumption firmly in the spotlight.
If we change our consumption habits, this would have a drastic effect on our environmental footprint as well
The analysis showed that household consumers are responsible for more than 60% of the globe's greenhouse gas emissions, and up to 80% of the world's land, material and water use. What's more, the researchers found that the footprints are unevenly distributed across regions, with wealthier countries generating the most impacts per household.