One Graph That May Make You Rethink Civilization

Before we dive into this post, let’s brush one slight matter aside. Climate change is real. Whatever our idiosyncratic biases may be — whether we accept that humankind has exacerbated the current trend toward a warmer Earth – climate does change. Twigs and pollen in the fossilized middens of Pleistocene packrats suggest that the iconic sunburnt deserts of Nevada and Arizona once (and geologically recently, at that) resembled the boreal forests of British Columbia and Alberta. Conversely, reaching much further back (around 50 million years), the world was warmer than today. Scientists have analyzed pollen and spores extracted from ocean sediment core samples that suggest palm trees grew in Antarctica during the Eocene. Truly, Earth is a dynamic creature.

During Duke University’s 2016 E.O. Wilson Biodiversity Days, a curious graph of long-term climate variability popped-up in lectures by NatureServe’s Healy Hamilton and the Nature Conservancy’s Mark Anderson. Several incarnations of the graph exist; however, the following is how the graph appears in the article, “Arctic climate variability prior to 100 years BP,” published on the Encyclopedia of Earth website (eoearth.org):

TemperatureChangeOver100KY_EOEarth
“Temperature Change Over the Past 100 ky [100 Thousand Years]” from “Arctic Climate Variability Prior to 100 Years BP” by Gordon McBean et al. (source: EOEARTH.org — Retrieved: 3/6/2016)
The graph depicts warm and extraordinarily stable climate over the past, roughly, 10 thousand years (nearly the whole of the Holocene epoch). I say “extraordinarily” because such stable climate appears unprecedented over the past 100 thousand years. Science, writing, agriculture, civilization — from the settlement of the Tigris-Euphrates River Valley to the construction of the Great Pyramids of Giza to the printing press to the iPhone — all of these human achievements fit in that brief period of stable climate. All history, organized religion (Zoroastrianism to Jedi), and governmental systems (Hammurabi’s Code to Communism) fit into that same period.

But what if we look further back? Paleoanthropologist Rick Potts, director of the Smithsonian Institution Museum of Natural History’s Human Origins Program, has argued that climatic extremes steered human evolution — that we owe our adaptability to necessity wrought from extreme climatic dips and spikes over our species’ formative millennia. Potts calls these environmental factors that spur hominin evolution “variable selection” (as opposed to but not mutually exclusive to geographical factors like “reproductive isolation”). Behaviorally modern humans first enter the fossil record around 40 – 50 thousand years ago, in the middle of 80 thousand years of dramatic climate change. Shortly thereafter (25 – 40 thousand years ago but still in this period of great change), Homo neanderthalensis disappears. And, around 13,000 years ago (on the cusp of the Holocene), Homo floresiensis dies-out, leaving Homo sapiens the last living representative of the genus. Likewise, the larger beasts — mammoths, saber-toothed cats, dire wolves, 2,000lb short-faced bears and other Ice Age behemoths — all went extinct around the beginning of the warm and stable Holocene.

Though myriad factors may have contributed to our species’ survival (and others’ demise), that our brains and bodies were forged through a chaotic climatic gauntlet can easily be argued. However, our systems and ideas — all that gives our species a sense of permanence and superiority — our ability to mark the world came in relatively easy millennia of mild climate and smaller beasts.

Homo sapiens are adaptable animals. Maybe, our ability to survive does not depend on certainty. But it seems that our ability to thrive — to leap-forward in technology, medicine and agriculture so we can nourish our many billions worldwide (a task that we have still not mastered) — does. What crops grow where? When do they grow? What can we do to help them grow? Surplus agriculture (the work of the few who feed the much greater whole) allows us to lead specialized lives away from the fields as doctors and engineers, instead of ranchers and farmers or hunters and gatherers. It seems civilization has taken advantage of a rare opportunity — the Holocene, an easy epoch — to domesticate crops and livestock. But what does that bode if the climate becomes less predictable or entirely unstable? So much media has focused on rising seas. But what about rising CO2 levels in the atmosphere, the unabated spread of forest-killing beetles, the greater rates of wildfires that alter the chemical balance of both air and soil, or increasingly acidic rain, soil and seas? (All effects of climate change.) Half the world now lives in cities without rows of our own to hoe, dependent upon and confident in the fertility of distant farms. How do we survive a meager harvest?

In an interview for KQED Quest (San Francisco PBS science broadcasting) Healy Hamilton has said, “Because there’s so much information in the world, we think that everything’s been discovered. We think that there’s nothing new. And the coolest thing about science is that you answer one question and it gives you 25 more questions.” What I love most about this graph and the work of NatureServe and the Nature Conservancy (among so many others) is how it becomes apparent that the Earth has so much left to teach and we have so much more to learn.

Interesting Stuff:

Arctic Climate Variability Prior to 100 Years BP” by Gordon McBean et al.

How Climate Change May Have Shaped Evolution” by Brian Handwerk –

Persistent near-tropical warmth on the Antarctic continent during the early Eocene epoch” by Jörg Pross et al.

Variability selection in hominid evolution” by Richard Potts

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