Tuesday, September 30, 2008

Maximum Life Expectancy

The first and third laws of consumption can be used with basic physics to project the maximum life expectancy of the human population.

First, the bottom line: Maximum life expectancy is 134 years. This can only be attained if the average speed of resource movement reaches the speed of light. At this point, there would be nearly 9.3 trillion people occupying the space of a sphere half a light year across. To keep such a population functioning, we would need the equivalent of teleportation (such as Star Trek’s transporters), capable of connecting an average of nearly 300 thousand people per second and enabling the consumption of an estimated two-millionths of Earth’s mass per year.

The time it would take to deplete all accessible resources would be one 55-billionth of the time it would take for a population of 40 million people to deplete its resources, where 40 million is the size of a community (“super-group”) where members could be aware of everyone else if they communicated for one hour a day for an entire year. The number of super-groups in the entire population would be over 233 thousand, or the number of hours in more than 26 years – roughly the number of years in a generation! (If these facts don’t twist your mind into a knot, consider the following: The maximum life expectancy is almost exactly five times the actual number of “years” I just quoted.)

If we could divide Earth’s mass equally among 12 billion people (roughly twice the number now in the world) one of those pieces would be all that we now have left to work with. Accessing the equivalent of those other pieces would enable our current population to last as long as cosmic events allow us to with no increase in life expectancy, but reaching the maximum life expectancy would reduce the longevity of our species to less than 500 thousand years.

Monday, September 29, 2008

Peak Profit Growth

Businesses measure their success by comparing their profits from one interval of time to another. Profit – roughly speaking, the difference between income and expenses – is generally used for several purposes: to enable future growth; to help the organization survive future decreases in revenue (anticipated or not); and (for corporations) to reward those people who helped pay for past growth (investors).

For a business to be considered successful, its profits must always be increasing. An investor who pays 100 dollars expects to be paid a certain percentage of that amount out of profits (“interest”) after a year; if the original amount plus interest is reinvested, then the same (or higher) percentage of the new amount is expected by the end of the following year. The business must also make enough extra profit to continue growing if some of its investors withdraw all of their investments. As a result, businesses try to grow exponentially.

The economic success of a country and the world is also measured in terms of growth, where “profit” is equivalent to the increase in Gross Domestic Product (GDP) from one year to the next. Economic activity and consumption of resources are closely tied together; so that as businesses or economies grow, consumption grows proportionally. Equivalently, the dynamics of consumption translate into equivalent patterns of money flow.

My combined population model (and the laws of consumption it embodies) predicts that world per capita consumption will stop accelerating this year and its growth rate will begin decreasing. If profit growth follows suit, which it should, then investment will decline; credit, which is a bank’s version of investment, will also drop. When per capita consumption (and overall consumption) stops growing entirely, the world population will reach its maximum size; after that, resource depletion will reduce consumption, more people will die than are being born, and the population will crash.

It is hard to ignore the similarities between my model’s prediction and those of the current economic crisis. Interpreted through the lens of my model, it appears as though speculators (whose job it is to anticipate future economic growth) expected growth to continue, assigning corresponding value to investments that turned out to be imaginary and ended up overvaluing those investments.

Thursday, September 25, 2008

Consumption Rule of Thumb

My analysis of consumption, population, and group sizes leads to the following rule of thumb. As the daily time taken by the average person in a community to interact with others (consume resources) increases by a factor of three, the community’s size and per capita consumption increase by the same factor, longevity (time taken for the community to deplete all of its resources) decreases by 90 percent, life expectancy increases by half a generation (a decade), and the required speed increases by a factor of nine.

Using one full hour per day, the life expectancy is one generation (20 years), the community has 40 million people, and the speed is one foot per minute. In 0 A.D., longevity for one hour of interaction was about 3 million years; it is now 2 million years.

Beyond a full day of consumption, with a population of one billion people, automation must be used to enable the required interactions for consumption and life expectancy to increase (with such “productivity” squeezing out more than 24 hours in a day). Put another way, the world depends on technology to entirely support more than five billion people.

Wednesday, September 24, 2008


In Maximum Community Size, I derived the largest size of a population of people who can consider themselves part of a community. I later defined a “world” as a collection of people who can usefully interact with each other (such as moving themselves or resources) over a year. These ideas led to my discovery of the first law of consumption; which, combined with the other two laws, can now be used to better describe such communities.

While a few people in any population will be able to process information at the maximum seven units per second, most people will process information close to the average of 5.5 units per second. At this rate, if another person represented a unit of information, someone could be aware of over 7 million people per year if attention was paid for just one hour per day; and being aware for every hour of every day would result in awareness of 17 million people.

When dealing with large numbers of things, most of us tend to group them. If instead of paying attention to people, we were only aware of groups (again, as units of information) and an average of 5.5 people constituted one group, then someone could be aware of more than 7 million groups over a year at one hour per day. Such a “super-group” would represent a total population of nearly 40 million people. Each additional hour per day devoted to this activity would add another super-group to the total population that the person was tracking as part of the “community.” If every hour of every day was spent, the maximum community size would be 954 million (or almost one billion) people.

Keeping in mind that this discussion is based entirely on theoretical possibilities in order to explore limits, let’s now see what the laws of consumption have to say about all of this.

It is reasonable to assume, based on historical data, that per capita consumption was fairly constant until the world’s population exceeded 300 million people; a single isolated super-group could therefore expect to live to the minimum life expectancy of 40 years. A population size of 300 million corresponds to between 7 and 8 super-groups, corresponding to (potentially) as many hours spent by each member with the others; this is interestingly close to one-third of a day, or a modern “work day.” If an average person needs 8 hours for sleep and 8 hours for personal activity (with limited exposure to others), 8 hours for social interaction may represent a natural limit to sustainable world population size – 318 million people. Indeed, if the population remained constant at this value, then the amount of total resources I’ve estimated for 0 A.D. would have lasted roughly 48,000 years if it was totally non-renewable.

In a world of fixed resources, the first and third laws of consumption strongly suggest that humanity has traded species longevity and time spent not dealing with other people for population size and longer individual life expectancy. In 1829, the world’s population exceeded a full day of (24) super-groups; at that time, I project that life expectancy was 61 years and there were 1,760 years of resources remaining if the population had not grown. There are now nearly 174 super-groups with a life expectancy of 69 years and 68 years of resources; the United States, by contrast, harbors more than 7 of those super-groups which are living much better than the average by effectively taking more resources from others.

Saturday, September 20, 2008

Personal Parallels

My personal situation currently parallels, in microcosm, the picture I have painted of the world. My wife and I are both unemployed and depending for our survival on resources (our savings and her unemployment insurance) which are bound to run out. Our savings, comparable to the biosphere, is generating paltry interest (renewable resources) compared to our expenses (consumption), while money from unemployment, like non-renewable resources, is not replenished.

Next week, my wife will be starting a part-time temporary job that effectively offsets her unemployment insurance. Such a contract job is the equivalent of the world finding more non-renewable resources. It is likely that most of those new resources will be used for expenses, with the rest used by me to find a job of my own. If I get a contract job, some of what I earn will be put into savings (replacing the source of “renewable” interest), and some will be spent to find a job for us to start when our contracts are over (there are no more new resources).

In the worst case scenario, similar to the business-as-usual scenario that I and others have projected for the world, my wife will be unable to start her new job and I won’t find one. To make our dwindling supply of money last longer (and avoid the equivalent of a population decline), we have several courses of action, some or all of which may be done simultaneously. We can limit our expenses (holding consumption steady or decreasing it to a survivable level); sell what we’re not using or can live without (consume our waste); or we can invest some of our remaining money in an account that generates interest that we can spend (use non-renewable resources to provide renewable resources).

Among our “expenses” is insurance; without health insurance we would be risking untreatable sickness (imagine a world without health care); and without car insurance, we would be taking unacceptable (as well as illegal) risks by continuing to drive, at least as long as we could afford a car (without fuel and replacement parts, the world’s cars wouldn’t last long). Losing our home, we might be able to rent an apartment for a while, camp in the woods, or wander the streets unprotected from climate or predators (including other people). All of this would resemble the world population peak, soon to be followed by decline.

As I write, the United States government is preparing to add half a trillion dollars to its already stupendous debt, buying defaulted mortgages to prevent an economic depression that would make the 1930s look like a shopping spree. At the root of the ongoing crisis is people’s urge to consume more without paying for it with new resources. Our nation can afford to do this, for a while, because ours is not an isolated population (just as my wife and I have family, friends, and credit card companies to help us in an emergency). But eventually the world must banish people’s ability to act on this unhealthiest of urges and focus on doing the equivalent of finding a new job and increasing savings.

Friday, September 19, 2008

Desirable vs. Achievable Consumption

Using the Third Law of Consumption, we can determine the amount that the average world citizen could consume (where the world is considered an “isolated population”) based on life expectancy.

With the number of years between generations (the “generation interval”) at 21 years and the minimum life expectancy at 40 years, a life expectancy of 65 years corresponds to a per capita consumption that is 15 times the amount for someone expecting to live 40 years. For a life expectancy of 70 years, the consumption ratio jumps from 15 to 27. If everyone lived to an average of 100 years, the ratio would be 720.

From the First Law of Consumption, we can estimate the average speed required to achieve different life expectancies for a given population size. A life expectancy of 40 for 6.9 billion people (roughly the current world population) years corresponds to 16 mph; a life expectancy of 65 years requires a speed of 250 mph; for 70 years, the speed is 430 mph; and for 100 years, we would need to be able to move resources at more than 11,000 mph.

The Second Law of Consumption tells us that even with the technology to move resources we will be severely limited by the amount of available resources, a fact which our population growth is already reflecting. According to my model, the depletion-related decrease in population is being absorbed by consumption, which in addition to growth is increasing the amount of depletion.

Adding life expectancy arbitrarily will only exacerbate the situation by drawing down resources even faster. If we consumed just enough resources to keep the population constant, we would have 65 years remaining at the current estimated life expectancy of 69 years, which would effectively only apply to a few (if any) survivors. It turns out that this strategy – keeping population constant by maintaining consumption – would only work for a life expectancy of 68 years, a point we probably passed in 2006. Unless we increase the overall supply of resources, a growing number of us are doomed to die sooner than we should.

Thursday, September 18, 2008

Jarvis's Laws of Consumption

If I may be so bold, I would like to propose three “laws of consumption” which embody my observations and modeling of how consumption, population, and life expectancy are related.

FIRST LAW: The mass of resources consumed per unit of time (“consumption”) by an isolated population is proportional to the square of the size of the population and is also proportional to the average speed that resources can be transported.

SECOND LAW: The ratio of the consumption of an isolated population over one interval to the consumption over the previous interval is proportional to the ratio of remaining resources for the two previous intervals raised to an exponent equal to twice the base of natural logarithms.

THIRD LAW: For members of an isolated population, the average life expectancy corresponding to a given per capita consumption equals the sum of the minimum life expectancy and the product of the generation interval and the (base ten) logarithm of the ratio of the per capita consumption to the minimum per capita consumption.

Tuesday, September 16, 2008

Renewable Technology

There is an important difference between the terms “renewable resource” and “renewable technology.” “Renewable technology” commonly refers to the set of tools, materials, and methods that enables people to use renewable resources to perform a certain function.

Renewable technologies often rely on the use of non-renewable resources. For example, a technology that converts renewable (replenished) energy from the Sun into electricity could include non-renewable metals and silicon that have been processed using non-renewable chemical products; in addition, it is likely to depend on a large array of non-renewable technologies, including transportation and electrical distribution.

We can judge just how “renewable” a technology really is by assessing the fraction of total resources it uses that are renewable (as defined by the Renewable R's). The optimum technology will recycle all of the materials it uses (if not the preferably replenished resources it processes) into like or other uses (replacement), and if necessary include components that are functional over a very long time (reliable).

Currently life is the only truly close to optimum technology, and Nature's biosphere provides this technology practically for free. The result of many millennia of development and testing through evolution, it would be very expensive (if not impossible) for us to create such a technology on our own. Alternatives on the horizon such as biotechnology and nanotechnology, one involving tinkering with existing life and the other with something totally different, carry the risk of inadequate testing leading to potential disaster.

Friday, September 12, 2008

Renewable R's

When a “renewable resource” is consumed by people in a given year, it's consumption will not diminish the overall amount of resources available during that year. There are at least three ways this could happen.

The first way is for the resource to be replenished from some external source. Solar energy is “renewable” because the Sun is constantly emitting light, which replaces the light previously absorbed by us and other species. Wind is renewable because it is (usually) replaced by more wind. Members of other species are renewable if they reproduce themselves faster than we kill them.

The second way is for it to be replaced by us so it can be consumed again. A trivial example is a sand castle, which exists for a short time in its artificial form and then dissolves into its original state. Most of what we consume, however, assumes a different and often unusable form when we are done (“waste”); if we started consuming our waste, the original resources would become effectively renewable because we would not be depleting our supply of raw resources.

The third way is to slow down how fast we consume resources. By increasing durability and efficiency (collectively known as “reliability”), we can get many years of use out of what we produce, reducing the need to use new resources for the same purpose. Insulating our homes, sealing water leaks, and using materials that last long are all examples of this.

Utilizing the “renewable R's” of replenishment, replacement, and reliability, we can go far toward reducing our load on the resources we depend on without diminishing consumption and population.

Wednesday, September 10, 2008

The Physics of Reuse

Earth's biosphere, what we commonly refer to as “Nature” or “Life” is constantly perfecting the art of reuse. Countless species that include plants, animals, and microbes ingest, process, and expel mass and energy, most of which can over time be used by others.

Mass exists either as atoms, joined atoms (called chemical compounds, found in one or some combination of gas, liquid, or solid), or unbound subatomic particles. Life is primarily concerned with chemical compounds, which may under specific circumstances be either inert or reactive. While inert compounds stay unchanged in the presence of others, reactive compounds join with others to form new ones, and in the process either absorb or release energy. Energy itself exists in any of several forms: chemical (exchanged between atoms), nuclear (exchanged between particles that form atoms), electromagnetic (carried by massless light particles), and gravitational (embodied in space and time, which connect everything to everything else). From a purely theoretical perspective, mass, energy, space, and time are likely to be manifestations of the same thing, ultimately indestructible and eternal in some larger sense that none of us will ever be able to comprehend.

Within the confines of our experience, however, Life “uses” mass and energy to maintain, propagate, and modify itself. Maintenance preserves the individual, propagation preserves the species, and self-modification includes not only reproductive experimentation (evolution) but also changing one's immediate physical and emotional condition. The grunt work of performing these functions is done by cells: biological micro-machines evolved over eons to build, tear apart, and move mass throughout an organism while managing the energy required doing so. When too many cells become disabled from wear and tear, reproductive errors or catastrophic external “modification,” the organism loses integrity and its parts are either disassembled for use by other organisms or more randomly broken down by non-biological processes for potential use over a much longer period of time (such as oil). Even artifacts, buildings and machines built by humans to control how they feel, will eventually be available for use, in some other form, by someone or something else.

Tuesday, September 9, 2008

Capacity Growth

An alternative to the one percent strategy is to increase the amount of renewable resources exponentially. Throughout my discussion, I have been using the terms “renewable resources” and “capacity” interchangeably, where they are both defined as the amount of resources we are able to use that is replenished on an annual basis. Capacity is more rigorously defined as the capability of replenishing a maximum amount of resources, where the amount of renewable resources actually consumed increases until the capacity is reached; any additional consumption is supplied by non-renewable resources. If we want to supply more renewable resources (reduce the drain on non-renewable resources) then we must increase capacity; and if we want to do it fast, exponential growth is a natural way to go.

My combined population model achieves its lowest amount of error in calculating historical population (from 0 A.D.) when the capacity is zero. Because the original amount of resources is large (1.7 quadrillion pounds), even a capacity equal to the initial consumption of 300 million pounds results in a fraction of a percent increase in error. The capacity is unlikely to be larger than the amount calculated from the world ecological footprint, which I estimate to be 6.9 trillion pounds; this amount results in a 2% increase in error for 2005, which is too large to accept. The smallest the capacity could be (other than zero) is perhaps the 100 pounds per person estimated to be consumed annually in 0 A.D. (roughly the weight of a person).

When dealing with exponential growth, the starting value has a critical impact on the growth rate required to reach a final value in a given amount of time. If the world were to start increasing capacity in 2010, the rate the model predicts would be necessary to avoid population collapse varies from 9% (for a starting capacity of 300 million pounds) to 52% (with a starting capacity of 100 pounds); if the capacity were 6.9 trillion pounds, the rate would be less than half a percent. Given the stakes, I would argue for using the 52% rate if the one percent strategy was impractical (where the fraction of total consumption supplied by renewable resources is increased by 1% per year). Of course in both cases consumption must ultimately be limited to a maximum amount, which is much more likely to draw resistance than a position on the appropriate growth rate.

If we depend on Nature for renewable resources (the easiest approach to growing capacity, since the “technology” is already available), and its physical limit is the maximum capacity I mentioned, we will at best be able to support the population we had in 1980 (4.5 billion people). The rest, nearly one and a half times more, will need to come from us.

Monday, September 8, 2008

The One Percent Strategy

I estimate that the world currently has 62% of the resources that it had in 0 A.D., a fraction that is decreasing by more than 1% annually. By the time it falls below 20%, less than 30 years from now, we will be forced to consume less each year, which will likely result in a decrease in population. If we are unable to increase the world’s supply of non-renewable resources to compensate for what we consume, then to avoid a loss of population we must increase our use of renewable resources.

This can be done by first deciding how much consumption we want to have (proportional to the square root of the population size we want). We could choose, for example, to freeze world consumption at what it will be in 2010, or we could choose to let it grow to twice the 2010 level. Once we are able to supply that amount by renewable resources, we won't be able to increase how much we use without increasing the supply.

Next, we need to decide when we will start increasing the amount of renewable resources that we use; keeping in mind that waiting longer will force us to work faster. If we start at the end of 2010, we will need to add about 1% each year to the fraction of consumption supplied from renewable resources (the “renewable fraction”) while keeping consumption constant at the 2010 level. If we wait until the end of 2020, holding consumption constant at that level, the renewable fraction will be 1.5%. Waiting until 2030 increases the renewable fraction to more than 6%. By the population peak (2037), the renewable fraction will be 9%.

The renewable fraction is proportional to the total amount of consumption that we choose as a maximum. With consumption limited to what it will be in 2010 and assuming we are not using any renewable resources, we will need to get 1% of what we consume from renewable resources in 2011. In 2012, we add 1% to get 2%; the following year, we add the renewable fraction to get 3%, and so on. If we choose instead to double the amount of consumption, the renewable fraction doubles to 2% per year; we are still starting to increase our amount of renewable consumption at the end of 2010, but we are allowing consumption to grow as it has until it reaches the limit (around 2031). Note that for any given year, using the previous year's consumption to determine how much renewable resources we will use will reduce the actual renewable fraction somewhat when we allow consumption to grow to a larger target value.

Sunday, September 7, 2008

Four Worlds

The outcomes of my combined population model match my definition of “worlds” – practically isolated systems that people inhabit: A small population (less than one-hundredth the present number) living off the land and the scraps of our civilization; a population a little larger than ours, limited to the Earth and relying on totally renewable resources; or a much larger interplanetary population, limited to the Solar System and using entirely renewable resources; or a population that grows and then sheds people, by death or emigration, while consuming no more than a maximum amount of renewable resources.

The first world would result from using almost entirely non-renewable resources. It could be realized between 50 to 200 years from now, depending on whether and how fast we acquire new resources.

The second world would be the result of extremely rapid growth of renewable alternatives to energy and production, with us using entirely renewable resources within 60 years. No new non-renewable resources will have been found.

The specifics of the third world depend on how fast we can acquire new resources. For it to exist at all, we would need to have enough non-renewable resources to offset the depletion of non-renewable resources being used to support the population and eventually accounting for all of our consumption (likely within 400 years).

In each of these alternative worlds, people would be limiting themselves to what can be regenerated on an annual basis. The conflict we are currently experiencing between competitors and cooperators will be present in each of these worlds as they deal with the necessity to curb consumption to the renewable resources that are available. In these cases where the speed of travel is limited, there would be no more resources for use in expanding the population and keeping it coherent; we would all need to become cooperators or at least restrain the behavior of competitors.

The fourth world would come into existence if the need of competitors to acquire more resources from themselves could not be controlled. The competitors could then either leave to start other worlds (emigration) or be allowed to kill people. Because the efforts of everyone are necessary to sustain consumption, overall consumption would drop with population, and resources would then be available for growth. The world would cycle between growth and death, growth and emigration, or some combination of both.

Friday, September 5, 2008

Expand or Die

In his acceptance speech for the Republican nomination for president, Senator John McCain summarized his primary philosophy of life, that all of us must fight for everything we have and hope to get, with country first. This followed a convention that promoted the world view that protecting, enriching, and growing the ranks of people like us is the duty of every American.

In a nutshell, this world view explains much of what has happened over the past eight years under ultra-conservative political domination: Military occupation and economic plundering of other countries, privatization of government, arbitrary detention and torture (of “others” who might pose a threat), domestic spying (finding the “others” among us), and environmental destruction (where the rest of Nature as simply a set of resources to be consumed). People who don't match their rigid definition of a “real American” as a Christian, heterosexual, economically productive Caucasian have been at best pitied, and at worst subjected to ridicule and restriction of opportunities to survive and thrive.

That many liberals choose to broaden the definition of “us” to include all of humanity (for some, even other species) is too much for ultra-conservatives to handle. They are lost in a world where “others” can't be easily identified and controlled; where behaviors rather than people are evil; and where survival depends more on cooperation than competition. Unfortunately for them, such a world is the one we currently live in, and pretending that it's something else can only lead to pain and suffering on a massive scale (as fundamentalists of other faiths and cultures continue to prove).

The “us versus them” attitude has had historical value. In small, relatively isolated groups, it has led to the evolution of different behavioral and physical attributes attuned to the unique environments where they reside. “Others” who did not have such attributes threatened the survival of the groups, which meant they either had to be assimilated, marginalized, or eliminated. As resources ran out and waste overcame them, groups needed to expand or die, which led to either conflict with occupants of areas they expanded into, or exploration and settlement of uninhabited areas that required a strong focus on taking risk for personal gain.

Most such groups have merged into larger communities with global reach (or are in the process of doing so). These larger communities are forced by common interest to cooperate with each other in an era where their actions can jeopardize the future of the entire human species. At the same time, our exponentially growing consumption of resources (such as fresh water, arable land, fossil fuel, precious metals, other species) and its attendant waste (pollution) is forcing our new global community to make the same choice its ancestors dealt with: expand or die. To expand, we will all need to work together as the problem is too big for any of us. If we choose to die, by complacency or mindless pursuit of self-interest, then competition will sadly become more valuable as resources run out and the environment gets more toxic.

Expansion cannot include the increased drilling and environmental exploitation that ultra-conservatives like John McCain champion. In fact, pursuing such a strategy will only make the problem worse, by adding waste and increasing the rate of depletion. What we must do instead is increase the amount of renewable resources we can use as fast as possible (and not using them any faster than they can regenerate) while limiting the amount of non-renewable resources that we use. We will need new non-renewable resources to be sure, but only to create and be able to use renewable ones. What this means immediately is that we must focus the majority of the world’s economic growth on developing our ability to use renewable energy, and reuse (or get more use out of) the products we make. What’s left of our growth should be spent acquiring more non-renewable resources to further this effort, without adding harmful waste; this may involve a serious and vigorous pursuit of the settlement of other worlds such as the Moon and Mars, a task well suited to those driven by competition and stressed by highly ordered and unavoidable social interaction.

There are those of us who are comfortable with fighting for what we want, and there are others who work best when we are cooperating with other people toward improving our common welfare. Both types of people are necessary in a society, but they must be free to be productive in their own way; otherwise they will clash and the resulting stress will become too great for all of them. There is no one left to fight except ourselves, and we can’t expect that learning to better live together will solve our problems. In the world we share today, converging toward a single community that faces the historical challenge of expanding or dying, the competitors need to be turned loose to find and develop new resources while the cooperators work on getting the most use out of what we have.

Monday, September 1, 2008

Strategy for Survival

Of the options for avoiding a reduction in population that I outlined in “Future Alternatives,” the mixed strategy (option 6) seems to make the most sense. One way or another, the world will be forced to support its population with new resources within the next 20 years.

My model projects that if we continue our historical increase in consumption (the “No Change” scenario), we will use 46 times this year’s consumption between 2009 and the population peak in 2037. By the time of peak, 144% of this year’s population will be consuming 210% of the resources we will this year. If we are not currently increasing resources, we may need to devote part of our consumption to this task, effectively reducing population growth in the process.

Holding consumption constant would give us a maximum of 17 times the amount we currently consume to use for resource growth. If we wait until 2014, we’ll have less than 10 years of that year’s consumption available. By 2019 we’ll have five years’ consumption available; and by 2024 we’ll have two years’ consumption available. At the end of 2027 we’ll have little more than one year’s consumption to use for resource growth, which is arguably the last chance we’ll have to avoid a loss of population.

If we focus on acquiring renewable resources, we will not need to continually add new resources to replace the amount that we use. We would get the most efficiency out of what we spend to get those resources, leaving remaining (and new) non-renewable resources for dealing with changes in conditions that might force alterations in infrastructure such as global warming.