Habitability Limit

Before humans had any significance influence on our planet, the population of a typical species was about two-thirds higher than in 1980, when humans began routinely consuming all of what other species “produced” (1 Earth). The total of other species with populations of 1980's size consumed nearly 1.9 Earths, which was all turned into biomass that could be consumed by others. That and the extra population consumed and recycled a total of 3.1 Earths, a measure of the total ecological resources of the planet.

As human consumption grew, other species had to do with less. The pressures of habitat loss, introduction of destructive species, pollution, and direct killing by humans caused their populations to decline, and in an increasing number of cases, go extinct. The survivors still needed the same amount of consumption for basic survival and, by extension, fulfilling their roles in maintaining the planet's habitability; but they needed to consume more resources to do so, since food was harder to find, and there was greater competition for what was left. Thanks to humans, the amount of remaining resources was shrinking a little slower than their populations, and they used all of it.

That's the picture that emerges from my latest research, based on projections of the Living Planet Index using my population-consumption model. We humans are currently consuming nearly 1.6 Earths, leaving 1.5 Earths for other species, of which they need a minimum of 1.2 Earths for survival (and are using the remaining 0.3 Earth to attain it). Because their minimum consumption is converted into both mass and function, at least 1.0 Earth is needed to keep our planet habitable (in economic terms, the “production” equivalent of their “capital”); this corresponds to human consumption of about 1.8 Earths.

If this analysis is correct, then we need to do everything we can to avoid reaching the maximum by lowering our consumption, preferably without casualties to our own population. My worst-case curve fit to our consumption over time shows that our consumption would peak when we're only within 6% of the maximum, which is close enough to add credibility that it is a real limit.

Populations

Several years ago, in “Half-Life,” I projected that the populations of other species, measured by the Living Planet Index (LPI), would reach the half-way point by this year (relative to its value in 1970). That isn't going to happen, mainly because humanity would need to be consuming 1.9 times the ecological production of the planet (“Earths”), and we are only consuming about 1.6.

This expectation is based on the notion, common in sustainability literature, that the sum of the ecological resources consumed by all species (including ours) is a constant. Further, it assumes that the consumption by other species are related to the size of its population as my current population-consumption model describes for humans. As I discussed in “Approaching the Peak,” our consumption appears to be climbing to a maximum of 2.0 Earths, which corresponds to an LPI of 0.46. I now project that if we manage to consume a little more than 3.1 Earths in a given year (a number very close to the constant pi), the LPI will be at zero, which is a euphemistic way of saying that we will have effectively killed the planet, and almost certainly ourselves. Note that this is another one of those strange rules of thumb: Consume up to one Earth to live sustainably; consume two Earths as a natural target (which may still coincide with consuming Nature's producers that we most depend on, and result in our population crashing), and consume three Earths to wipe out everything.

The U.N. recently reported its own projections for population and consumption in 2050. I was able to reproduce its numbers by performing curve fits on population and the consumption that I had derived in my recent modeling (see “Discontinuity”). As I did, they may have used three possible scenarios for population and consumption to derive their expected values. In my case, one of the scenarios is a “worst case” curve-fit, showing our population peaking in 2028 and dropping to zero by 2073; as our consumption falls, other species will have more to work with and their populations will rise after bottoming out at an LPI of 0.57. Another scenario is my population-consumption model's gradual leveling off as consumption stabilizes. The last scenario is a best-case curve fit, with our population and consumption rising rapidly, at the expense of other species, who die off by 2029. Combining these three scenarios using a PERT estimate is what yielded the U.N. estimates, which, if it meets the definition of “expected case,” will finish off other species by 2041, and likely us too.

Trust

We all have limited experience and knowledge, but this doesn't keep us from having to make decisions about things we are personally next to clueless about, or powerless to directly affect. For such decisions, we often depend on others we trust, who appear to have relevant knowledge, abilities, and experience that we don't. That trust tends to be based on our assessment of how much those others would agree with us on things we do know about. Conversely, the more different someone is from us, the less likely we are to trust them to do anything, especially if the potential cost of letting them is especially high. This dynamic applies to a wide range of situations, including who we vote for (in a representative democracy), what we buy at a store, and who is guilty in a court trial.

Trust also depends on our shared values. In my personal value system, a “good” decision is one that maximizes satisfaction and health for everyone who will be affected by the actions taken in its aftermath, with priority placed on the latter. Some would argue that it is they who should experience maximum satisfaction, and it doesn't matter what happens to anyone else as a result (they might even consider the diminishing of other people's health as a source of satisfaction). Others might quibble that “satisfaction” includes “health”; I've included both to ensure that health is taken into account regardless of the immediate goals of the decision.

As our experience builds with those we trust, we will either gain or lose confidence in them, and will either limit or expand their role in future decisions. Sometimes, however, we have no choice, such as when children must trust their parents or guardians to keep them safe. In such cases, the trust is often backed up by a society that imposes strict penalties for abusing it.

Our societies and their institutions are also held to standards of trust, by the citizens who are part of them, and dependent on them for what they can't do themselves. For example, the economic crisis that started in 2008 was precipitated by the abuse of trust by banks and their insurers. The U.S. government – as an agent of society – was entrusted with keeping them honest and their customers safe from fraud; yet that trust too was abused, and to date neither the institutions nor the government have taken adequate steps to ensure that they can be trusted about such things in the future (though people still depend on them, largely because they have little choice).

This brings up the question: What can people do if they have no one to trust when they are lacking what it takes to meet their needs on their own? Under such conditions, they may begin to form new associations, or even new communities, that are more trustworthy. The alternatives may even coexist with the original, untrustworthy ones until either trust is restored in the originals, or the originals lose all their power because no one trusts them any more. If no alternatives exist or can be constructed, then tragedy may result: slowly, if the originals still have some capability to meet people's needs; or quickly, if they have already fallen (the political variant of the latter is anarchy, where it's literally “every man for himself”).

Unreasonable Doubt

Global climate change is perhaps the most visible consequence of humanity's disruption of the Earth's natural systems, and is therefore at the center of the worldwide debate over how much – if at all – we should accommodate each other and the rest of the biosphere in our pursuit of personal happiness.

In a way, it's like a criminal trial, where the most economically successful people are accused of causing suffering and death on a planetary scale, disproportionately felt by the least economically successful people and other species that are even more powerless to defend themselves, along with future generations of everyone and everything. As in a trial, there is an underlying truth, whose discovery is a critical part of a process to determine whether or not the defendants should have their behavior restricted. The ultimate test of whether the trial is successful is what happens later: who and what may be harmed as a result, and how much.

It doesn't help the plaintiffs' case that the “prosecutor” and “judge” are both being paid by the defense, and that the jury is stacked with defendants and people who are sympathetic to the defendants. To further ensure a verdict of innocence or a hung jury, the standard of “reasonable doubt” has been distorted by the judge to mean “any doubt,” which is unavoidable in even the most favorable of situations.

Undaunted because they know that if they lose, everyone dies, the plaintiffs have gone forward with their case. Until recently, the bulk of their evidence has been circumstantial, but the defendants have become so brazen and powerful, and the damage so great, that even the “any doubt” test is rapidly becoming possible to pass. This has led the defense to move preemptively to disqualify the new evidence while conducting a misinformation campaign aimed at confusing a growing number of jurors who are daring to think for themselves. The prosecutor has objected to this behavior, but there is no assurance that the objection won't be overruled.

To understand this dynamic, it is important to recognize that the “defendants” face their own form of existential threat if they “lose.” This comes from their identity with the power they have gained in the process of seeking more happiness than anyone else. To cede any of that power, or to change their values so that they view its acquisition as wrong, would be to diminish their self-worth – and in their minds, suffer direct injury to themselves. It is also easier to change perceptions than reality.

Obviously, I side with the “plaintiffs” in this “case,” even though I am technically one of the “defendants.” If my analogy has any validity, it points to an important psychological requirement for success in limiting (if not outright stopping) the harm we are doing to ourselves and our relatives in the web of life on Earth. That is, we must all learn to redefine our self-worth in terms of our being part of others, instead of how much we are apart from others. We also need to be supportive of each other as we experience the inevitable pain of acknowledging our role in causing pain; this is the essence of forgiveness as a part of the process of both healing ourselves and healing those we have harmed. In the trial analogy, the penalty to be paid by the defense is to share the lives of the plaintiffs in a joint effort to make us all better through the application of mutual strength rather than personal strength.

Approaching the Peak

I just empirically derived the logistic function for world population growth. As I described in the post “Discontinuity, ” humanity has been able to approach the maximum limit to consumption of ecological resources by radically increasing what I call the “extraction mass,” and the new analysis shows that our population growth is adapting just as populations of other species do when faced with similar constraints: by reducing population growth through competition.

Our consumption is converging toward a value that is twice the amount of renewable resources that the natural world produces (its “biocapacity”). Since 1980, we have been consuming both biocapacity and “natural capital” -- the parts of the biosphere which generate that biocapacity. Natural capital recycles as well, by an amount that appears to be equal to biocapacity, accounting for the other “Earth.” This is the ultimate power of our technology: to destroy our planet's mechanisms for sustaining life. If we ever reached that limit, we would either need a totally artificial life support system (for us) or our population would crash, perhaps never to recover.

My analysis indicates that the maximum population is 8.69 billion people, based on the current value of extraction mass (which, together with the apparently constant “transaction mass,” determines consumption). World population is currently about 7 billion, and is projected to be within 10% of the peak by 2023. For contrast, in 1980, when we were consuming just all of the biocapacity, the population was 4.53 billion; this is how many people a healthy world could support at our current average lifestyle (represented by extraction mass).

Ironically, if we hadn't increased extraction mass right after World War Two, from an equivalent ecological footprint of 0.018 hectare to 2.5 hectares, the maximum population (for consuming two Earths) would have been 29.09 billion people, and for consuming one Earth it would have been 20.48 billion people. More people could have lived, but they would have had a lower life expectancy (at the peak: 55 years for one Earth and 58 years for two Earths) and happiness (42% for one Earth and 47% for two Earths, again at the peak). At our present population, the average world consumption would have been 8% of its current value, life expectancy would have been 45 years, and happiness would have been 30%.

Evidence continues to accumulate that biocapacity has been degraded by our consumption of natural capital – effectively overwhelming the natural world. Not the least of this evidence is related to global warming, which at this point may be unstoppable. The most obvious consequence is a reduction in the maximum population, and I'm afraid that the only real control we have is with the variable that pushed us so close to disaster: our lifestyle. It may be inevitable that mortality will increase, and it will come from either growing competition as we approach peak population, or less time for each of us to make an impact as we let the natural world have more influence over our lives. 

Discontinuity

Last week I thought of a more general form of the relationship between population and the consumption of resources. Preliminary testing suggests that it's much more robust than previous versions of my population-consumption model.

You may recall that I had identified what I called “transactions” as the only mechanism determining how much mass people will convert into waste each year. People extract resources from wherever they are, process them into useful forms, and exchange the results with other people. If everyone in a population conducts one transaction per year with everyone else in the population, the total number of such transactions is one-half the square of the total number of people. The average mass for each such transaction is what I call the “transaction mass.” With transactions accounting for all consumption, transaction mass included both the mass of stuff exchanged and whatever was used to do the exchange (such as fuel used in transportation).

In the new version of the model, I've redefined transaction mass as only the average amount used to perform an exchange. The majority of the total consumption is what is actually consumed by people. Each person in the population, on average, consumes an amount of mass which I call “extraction mass” (because in the simplest case each person could extract resources on their own). Total consumption is the sum of the transaction mass and the extraction mass, and per capita consumption as a function of population ends up being a straight line.

When I was assuming that total consumption varied with the square of the population in an isolated population like the Earth, all that was required to determine how it changed over time was a set of historical population numbers and a value for consumption at some point in time. As a proxy for consumption, I used the global ecological footprint, which measures the per capita ecological impact of humanity on a global scale, and the starting value was assumed to be the minimum reported for countries in 2006. I then did an elaborate curve fit of consumption, constrained so that when projected to the present, it matched the most recent measured value. Projecting consumption into the future showed that it would peak and then drop; and since it was interdependent on population, population would likewise peak and crash.

The new version of the model was inspired by an attempt to simply describe and justify the elements of the previous one, including some inconsistencies with current data that couldn't be easily explained. Specifically, recent estimates of ecological footprint show very little change over the past fifty years; and per capita world energy consumption shows the same pattern, even though population more than doubled over the same period. In contrast, the previous version of my model shows a steep change in the equivalent per capita consumption. If the trend of the data was consistent over all time, early civilization should have been consuming almost as much as we are today, and living just as long, which was clearly wrong. It was natural to assume that the flatness of the data was a historical fluke, but as I was testing my assumptions, I realized that such an explanation was unsatisfactory. Unfortunately, even with the new version the problem remained.

Then I realized that I had a way to measure per capita consumption going back much further in time than the footprint and energy data. In addition to historical estimates of population, there are also estimates of life expectancy, and I've known for a while how life expectancy and footprint are empirically related. I could therefore use life expectancy as a way of calculating footprint, just as I have used it to convert my projections of footprint into life expectancy (and, similarly, happiness).

The results were astonishing. For one thing, ten thousand years ago, the ecological footprint was one-fifth of my previous estimate of the minimum footprint. The transaction and extraction masses stayed effectively constant right until the middle of the last century. From 1950 until 1960 (the decade I was born), the transaction mass jumped by a factor of nearly 30, and then stopped changing; meanwhile, the transaction mass remained what it had always been. The footprint (and presumably all per capita consumption) looked just like a mathematical “step function,” corresponding to an almost doubling of life expectancy. The reasons for this near-discontinuity in the historical trend likely involve a combination of major advances in medicine (such as the development of antibiotics) and the widespread availability of fossil fuels and oil derivatives for nearly every purpose, not the least of which being the creation of artificial fertilizers that could immensely increase food production.

Perhaps the most important prediction of the previous version of my model was the impending crash of the world's population. I have so far been unable to find evidence for such a crash in the new version. The closest I can come to justifying such an expectation now is the existence of the step function itself, an understanding that the oil that powered it is becoming much harder to get, and the clear evidence that we have exceeded the ecological carrying capacity of the Earth and may soon reach a tipping point in Nature's ability to support us. To the extent that the previous version does an excellent job of curve-fitting population over time, and population is the main variable in the new version, it may yet prove to be accurate in at least that one regard.