The ancient Greek philosopher Protagoras is famous for his saying that man is the measure of all things. Though we don’t know much about Protagoras or his written work except for quotations appearing in other ancient works, the general view is that Protagoras was the father of moral relativism in philosophy.

The Protagoras’s complete statement has been translated as follows: “Of all things the measure is man, of the things that are, that [or “how”] they are, and of things that are not, that [or “how”] they are not.” It is unlikely that Protagoras believed that physical truths about the natural world such as the freezing point of water depended on one’s personal standpoint.

But under Protagoras’s tutelage in matters of values, we are left only with the measuring instrument called “man” (or more inclusively “humans”). In the age of the Anthropocene—that still-not-official geologic age in which humans are designated as the most potent geologic force on the planet—those issues thought to relate solely to the lives of humans do NOT, it turns outs, relate simply to humans.

While we may choose to celebrate the material progress of humankind, we do so heedless of the wider costs to the stability of the biosphere. Those who focus only on measures that exclusively relate to what we regard as human well-being miss the broader picture and mislead their audience. (They often say “the world” is getting better when they mean certain measures of human well-being are moving in a direction we regard as good.)

But, human civilization thrives under very specific environmental conditions, namely the ones experienced since the end of the last ice age. That age, the Holocene, has been marked by a moderately warm and stable climate which made possible agriculture and the concomitant rise of cities.

General advances for humans such as rising incomes (and thus consumption) and better access to health services are unalloyed positives only if the continuously degrading indices of biospheric stability are ignored. Two concepts, planetary boundaries and tipping points, inform us about the risks.

Planetary boundaries identified by the Stockholm Resilience Centre number nine and include such things as climate change, ocean acidification, ozone depletion, and biodiversity, called “biosphere integrity.” The Centre reports that humans have passed four of the nine boundaries: “climate change, loss of biosphere integrity, land-system change, altered biogeochemical cycles (phosphorus and nitrogen).”

The word “boundaries” implies that with the right actions we could cross back over them and thus return to a safe zone. (In practical terms this would mean moving back into a zone of lower risk.)

Tipping points, however, imply a journey to the land of no return. Researchers reporting on the planetary boundaries believe that in the areas of climate and biosphere integrity, the planet is in danger of moving toward a new irreversible state, “a much less hospitable state, damaging efforts to reduce poverty and leading to a deterioration of human well-being in many parts of the world, including wealthy countries.”

I am reminded of the man falling from a 100-story building who, when asked at the 50th floor by someone near a window how he’s doing, replies, “Fine so far.” Tipping points seem unimportant or even nonexistent until you reach them. Conceivably, human well-being could on average continue to increase for many indicators for years to come, only to be dramatically reversed when planetary tipping points kick in.

The mathematical way of talking about this is that tipping points can represent a kind of step function or nonlinear response on a graph. Much of the sanguine talk of continued human progress is premised on the absence of sudden nonlinear turns or step functions in the graphs of the key indicators of planetary health. The data to date give us little reason to expect gradual change for all indicators or to believe that we can adapt successfully to all the changes we face if we don’t alter our current course.

It is not surprising that humans look to themselves as arbiters of what’s important in the life and processes of the biosphere. Humans, like every other species, seek their own survival and well-being first. But our overreliance on humans as the measure of all things is the very posture which has put us on the road to potentially catastrophic changes in climate and other planetary systems, changes that threaten our very survival.

The time has come to put away man as the measure of all things and look to much broader measures for an assessment of our well-being and the well-being of all those systems upon which ours depends.

Image: Democritus and Protagoras. Salvator Rosa. Oil on canvas (1663-4). Musée de l’Ermitage. Via Wikimedia Commons