In chemistry, the study of how various inputs combine to constrain – or enable – reactions, is called stoichiometry – a fancy word that describes the phrase ‘… as good as the weakest link.’ Stoichiometry describes how we can have an abundance of inputs, but if we’re short of one, it stops the reaction. This concept is highly relevant to human societies as well because, any growing system is limited by the scarcest necessary resource. For instance, economists are confident that if society demands it, a substitute for phosphorus fertilizer will be found to continue t he “green revolution” indefinitely and propel our population well into the double-digit billions in future centuries. Except – spoiler alert – phosphorus is an element, thus inherently impossible to develop a substitute for in living systems (and, incidentally, a limited resource which costs increasing amounts of energy to extract). As we look closer at the human (and non-human) futures, we might be wise to consider what the limiting inputs are to our future expectations – and ecosystems. TaaL: The current human economy is even more complex than biological systems and depends on many inputs. You can now buy a rechargeable electric car with lithium batteries, but if everyone on Earth had one, that would pretty much use up all Earth’s lithium forever before they could buy a second one. Modern electronics use a lot of elements known as “rare earths”; wonder how they got that name? Hypersonic aircraft work best when made of titanium, but there isn’t all that much of it, and like all other ores, it’s getting mor e marginal. For the last two centuries of cheap and increasing energy availability, it was reasonable to assume that any element you might utilize was indefinitely available to you in any quantity, extracted from the far corners of the Earth, refined, and delivered to your door. But exponential growth has a way of quickly finding the “limits to growth,” and the nature of those limits may come as a surprise to you. Liebig limits can be subtle things, like a ship’s crew all coming down with scurvy because – as one of evolution’s little jokes - your species lost the ability to synthesize vitamin C possessed by most other Earth mammals. So, for centuries, going to sea could mean your teeth falling out, spontaneous bleeding, insanity, and death from infections, all for the lack of something nobody knew existed. Toothless, bleeding crazy people could hardly be faulted for missing that. But healthy humans can, and do, ignore utterly obvious limits, and indeed that is a defining aspect of current human culture. One dramatic example of ignoring Liebig limits currently in human news is the idea to colonize Mars. You’d think that as a space -traveling alien myself ( when I can’t avoid it – frightfully boring even if you’re a hibernating species like mine ),
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