No, Earth is not running out of resources.
Why is earth not running out of resources? Which resources could run out and how do we know that we have enough of them? We’ll have to clarify what we mean by a “resource” and “running out”.
I am running out of milk. Milk is a resource in my apartment and I don’t have enough of it for a second cup of tea today. Am I “running out of the milk resource”? No, because I can go to the supermarket and buy more milk, and the supermarket can get more milk from a dairy farm, which gets it from cows, which make milk from water and grass, and nobody is claiming that we’ll run out of grass.
When I urinate, the water eventually ends up in the sea, gets evaporated and rains onto fields to water grass and make new milk. So, the planet will never “run out” of milk. There might be a war that stops production or maybe a new type of grass-killing virus or some other issue that interferes with milk production but these are contingent problems that depend on the details of how the world is managed, not hard physical limits that cannot be overcome no matter what we do.
For the rest of this post, I will use the phrase “run out” in the ultimate sense rather than the contingent sense: I can contingently run out of milk, but the supermarket can supply more milk so it’s not a case of ultimately running out of it.
Is the world running out of drinking water? No, because water is not really created or destroyed on earth. It just changes form from clean, to dirty, to salty, to clean. This usually happens naturally via the water cycle which most people learned about at high school. In some places, humans convert more of the “clean” form of water into the “dirty” form than the natural water cycle can deal with. This is “running out” of water, but only in the sense that I am “running out” of milk for my tea. They need to go to the water supermarket and get some more clean water.
The modern version of this is called desalination - the conversion of salt water into clean water and brine. Over time the financial and energy cost of desalination falls as the technology gets better.
The technology for desalination can never exceed a certain thermodynamic limit though. You cannot get 1 cubic meter of fresh water (enough water for 1 person for 1 day) from salt water for less than about 0.7 kWh of energy. But 0.7 kWh is not very much energy. To think of it in terms of power, 0.7 kWh per day is just 29 watts or about half of a single lightbulb - a pathetically small amount of power. With today’s technology, we cannot quite get to get to the 0.7 kWh/m³ limit, we’re at something like 2-3 kWh/m³, but that’s still a very small amount of power (~100W per person, roughly equal to the heat from your body).
So, even if there was no natural water cycle we would not “run out” of fresh water with today’s level of technology.
But what’s the ultimate limit? How many people can we provide fresh water for? Would we run out of water in the oceans? No. The oceans are unimaginably large, roughly 1,000,000,000,000,000,000 m³. That’s 1 followed by 18 zeros, or a billion billion.
So is there a limit at all? Yes. The ultimate limit is that ~30W per person - at some point, there would be no way to reject enough waste heat to space without cooking us all. But that limit is a long way off - earth radiates about 100,000,000,000,000,000 W of waste heat already, and this is a good ballpark estimate for how much more we can radiate without the temperature rising too muchᵃ. A person radiates 100W of waste heat, but realistically people will also have other processes happening that supply them with food, water, transport, manufactured products and entertainment. Right now that power consumption comes to about 10,000 W/personᵇ. Given our waste heat budget of 100,000,000,000,000,000 W, we cannot ever have more than about 10,000,000,000,000 (ten trillion) human beings on the planet. This is 1000 times more than we currently have.
EDITED 06/01/2021: The waste heat budget of Earth can fairly easily be increased by using hot radiators and active cooling of the living space. Continent-sized radiators at about 1300°C radiate about 1000 times more heat than the ordinary, normal nighttime surface of the planet does. Incoming sunlight is at 5000°C, you can run a fine heat engine between those. This increases the waste heat budget to 100,000,000,000,000,000,000 W or 100 exawatts. Dividing by 10,000W per person, we get 10 quadrillion people.
As long as we stay under the ten quadrillion number, we will not run out of water, ever. We could have ten quadrillion people living on earth for the next billion years and not run out!
Is there any other physical resource that we might run out of? Oxygen, metals, fertilizer? Phosphates? Food? Clean Air? In short, no. Why? Because these things are not created or destroyed on earth, they are merely transformed into a different form and can be transformed back for a certain energy costᶜ. And those energy costs vary, but not by much, and the ones that we need more of like water tend to be a little cheaper. All those energy costs are included in a power budget of about 10,000W per person.
Where can we get all the power for this? Well, the Sun, of course. The sun radiates 384 yottawatts of power. How much is 1 yottawatt? It’s a lot of power, more power than you can comfortably imagine: 1,000,000,000,000,000,000,000,000 W. And that’s just 1 part in 384 of The Sun’s output. Earth itself cannot handle this, the waste heat limit of Earth is 300 million times lower. So we only need to capture a tiny fraction of The Sun’s power to fully populate Earth. This will happen using solar panels but those will soon be augmented by space-based mirrors to beam more sun down, probably in conjunction with an infrared shade to reduce the infrared that Earth gets from the sun in order to prevent global warming.
Even space for trash isn’t limited, because waste dumps and landfill sites will eventually be mined for usable resources. It just takes energy to transform it back into a useful form, and we have much more of that than we need.
All the different substances and physical resources that we think about - coal, clean water, food etc can be summed up into a single resource called negentropy: sunlight comes in, waste heat goes out, entropy increases and useful work is done (such as purifying water). Surprisingly, physics tells us that the only resource that ultimately matters is the cold nighttime sky to get rid of waste heat, and solar energy coming in from space. Everything else can be made from that!
What about living space? Will we “run out” of space if we have 10 quadrillion people on earth? No, not if we are prepared to build upwards and have artificially lighted spaces. Contemporary artificial lighting doesn’t feel natural, but it is nowhere near the limit of what is possible. The Coelux system shown here mimics natural sunlight so perfectly that you can barely tell the difference, and of course over time these systems will get better and cheaper.
If one builds 300,000 storeys of continuous structure on all the land on earth, one gets about 50 trillion square kilometers of living area. This is enough for each of 10 quadrillion people to have 5000 square meters (about 50,000 square feet - that’s the size of a mega-mansion) to themselves. This could include artificially lit interior wilderness spaces with artificial skies, artificial weather etc that are maybe 10-20 storeys high, and with the significant advantage of being less crowded, safer, having better and more predictable weather and being easier to get to than wilderness we have today.ᵈ
Such a planet sized city or ecumenopolisᵉ is limited by a combination of waste heat rejection and living space. 10 quadrillion people each with 5000 square meters per person on average, times 2.5 meters per storey gives about 12% of the volume of Earth - a spherical shell 400 kilometers high all over the planet.
It will take a long time to build and populate an ecumenopolis, hundreds of years. And when we get there, it is likely that off-world colonies in the Asteroid Belt will need even more people - up to 1 quintillion, likely limited by matter availability. The journey from contemporary Earth to the first trillion people will involve a lot of innovation, science and technological change. We will need to push new technologies, colonize space, etc. It won’t be easy, but the journey from our humble beginnings - just 10,000 people - to where we are now also wasn’t easy. What I have sketched here doesn’t require violating the known laws of physics or inventing anything fundamentally new, just pushing further in the direction we are already going in.
In summary, Earth is not running out of resources in the ultimate sense. There are many temporary, contingent shortages caused by wars, incompetence or various institutional failures, but planet Earth can support 10 quadrillion peopleᶠ in extreme luxury indefinitely without anything running out assuming present-day science is pushed to its maximum potential and is used to provide things that people really wantᵍ. Those may be unrealistic assumptions, but the obstacles to progress are not a lack of resources.
ᵃ Doubling the thermal energy radiated by earth raises the equilibrium absolute temperature by the 4th root of 2, that is a 19% temperature increase from 287K to 341K, or 67°C.
ᵇ See Sustainable Energy - without the hot air, §18, where consumption is listed as 195 kWh per day per person; dividing this by 24 hours in a day gives about 10kW or 10,000W
ᶜ Helium can actually be permanently lost from Earth as it is light enough to escape from Earth’s gravity purely through thermal motion, and is one of the few things that could actually “run out” in the ultimate sense. However, the solar system contains huge amounts of helium in the gas giants - more than we will ever need.
ᵈ The value of convenience shouldn’t be underestimated here though - I haven’t been to the wilderness for many years because it’s inconvenient to get to, not something you can just do after work without planning and costs, and because it is currently winter in Europe; this is the reality for many people alive today. Wilderness wandering is expensive and inconvenient.
ᵉ Isaac Arthur’s video on this topic is a great resource.
ᶠ Though some exotic ideas like megastructure-sized thermal superconductors might be able to beat even this limit
ᵍ If we aren’t actually running out of resources, why do people say that we are running out of resources? I think this comes down to politics: we may not be running out of anything in the ultimate sense, but in the here-and-now it is convenient and indeed necessary to make people curtail their consumption. If milk was free at the supermarket, someone would take it all and dump it in the river just for fun, and then I couldn’t have my tea. A false belief that resources are “running out” serves as a second layer of costs on our consumption (Though a very economically inefficient one, as people’s intuitive beliefs about what they should conserve are way worse than a proper price system, and voluntary conservation doesn’t send price signals to suppliers so is ultimately self-defeating as it creates artificial shortages in the long term). It’s also a way to control people and it makes for a good belief-system or quasi-religion, complete with rituals, meetings, books etc; an “Eco-religion”.