HOMO SAPIENS NOCTURNALUS
On the last day of the Cretaceous, a small rat-like creature sits just inside the entrance to her burrow waiting for dusk to deepen so she can venture out. Below ground it is cool and comfortable, but the daytime temperatures are deadly to all mammals, yet not the huge dinosaurs that dominate every environment across the globe nor the majestic flying pterosaurs and the tiny winged things we now call birds.
The little hairy rodent, about average size for all mammals on this day 65 million years ago, catches a glimpse of the moon rising and the bright white new star in the sky that has been growing brighter every day since it first appeared several weeks earlier. The animal, our ancestor, can’t know that the light is an approaching asteroid the size of Mt. Everest. Tomorrow it will strike the Earth just offshore in a place humans call the Yucatan, and the impact will essentially destroy all global environments but liberate the mammals from their behemoth reptilian overlords. Eventually the Earth’s climate will cool down from the Cretaceous sweat lodge temps and mammals will rise up to rule the planet.
We humans have our limits, we do. Being mammals, we evolved to withstand dramatic temperature swings in the environment day to day and season to season. But we cannot tolerate sustained temperatures outside much above 100 degrees Fahrenheit, particularly if the heat is accompanied by a heavy dose of humidity. Once above 110 degrees, it is dangerous to work out of doors in the sun even for an hour or two; at 120 degrees it is impossible.
During the Jurassic and Cretaceous, much of the world was a hot house that dinosaurs thrived in. But the mammals could not tolerate the unrelenting heat, so they burrowed underground and stayed there for 125 million years. Our ancestors were all, to the very last species, nocturnal. When the sun set, the creatures with fur welcomed the cooler night temperatures and could roam about without fear of the saurian predators that stalked the lands on scaly three-toed feet in daylight.
Today, carbon dioxide levels in the atmosphere stand at just above 400 parts per million. In the Cretaceous, carbon dioxide levels were more than two times higher. At the current rate of increase today, the Earth’s atmospheric carbon dioxide burden will approach levels early in the next century that were extant when dinosaurs claimed all the world’s real estate as their own. If you are a mammal, and you are, that can’t be joyous tidings.
At the turn of the 22nd century, much of the vast interior of the United States may be uninhabitable, either that or all activity will have to be carried out during the day in air conditioning or in underground buildings. No physical work will be able to be performed outside when the sun is out. Most croplands in the Southwest, West, southern Plains and the South could be rendered unproductive because portions of the nation will be too hot for plants to thrive, too dry, and, in some areas, too prone to catastrophic flooding. Already, in the early decades of the 21st century, drought is withering great swaths of the West and creating conditions that span massive forest fires that eventually will utterly change the great forested landscape for good. In the South, hundred-year storms are becoming commonplace, and their ferocity is steadily on the rise.
As the heat comes on, and it will, there are only two options open for humanity over the next few centuries: hundreds of millions and perhaps billions of people will have to pick up and move toward the poles or to higher and higher elevation, or humans will have to burrow underground and, frankly, stay there.
Our mammal ancestors, ten million years after the demise of the dinosaurs, were faced with just such a dilemma. At the boundary between the Paleocene and the Eocene epochs 55 million years ago, temperatures soared once again to mimic the atmosphere than dinosaurs once found to their liking. But, then, it was the mammals that were out in the sunshine as the continents began to bake and warm seas invaded millions of square miles of land. There were three options open to mammals at that time: either return to the sea and evolve flippers and blowholes in the head to cool down, burrow underground once again, or head for the highest latitudes on the planet. At the very end of the Paleocene, crocodiles could be found at the Arctic Circle, basking beneath palm trees. Fossilized crocs and palms are plentiful in the rock strata in northern Canada.
Imagine it’s the year 2500. A new species of humans, Homo sapiens nocturnalus, has evolved in a geological eye blink. These people are just like humans of the 21st century, but their physical stature is far smaller, about half the height of their ancestors. Their small, lean bodies allow them to radiate heat away rapidly – a survival adaptation. Their faces would be familiar, but their eyes are beginning to evolve to see better in low light. They are omnivores and have returned to a hunter gatherer lifestyle. They eat meat when they can hunt it down in the early morning or evening hours, and gather desert plant foods during those hours, as well. In their carved underground shelters, these new humans cultivate dozens of species of edible fungi to enhance their rather limited diet.
They have left the daylight world for the darkness underground, because like the Cretaceous rats, they can’t spend any time outside during the day, except perhaps for brief hours during the months of December and January. Inside limestone bluffs all across the midlands of the former United States, these diminutive people have carved great living corridors in the soft rock, complete with living spaces, store rooms, manufacturing dens, toilets, and meeting spaces. All the square footage is cool, but not cold, the temperature generally in the sixties when all residents are inside and their body heat is trapped in the airy spaces amid the rocks.
Most modern humans have disappeared from the latitudes south of the 55th parallel. People genetically identical to us today are now clustered around northern James Bay and on the northern coasts of Canada or stretched out along the former tundra regions of Siberia and Scandinavia. In these regions, temperatures are tolerable even during the endless Arctic winter nights. Life is familiar, though much of the former technologies of the 20th and 21st centuries have been abandoned for lack of resources, particularly rare metals needed to manufacture the electronic devices of yore, and the collapse of the commerce of capitalism long ago.
Back to the 21st century: October, 17, 2017. Here in northern New England, we experienced our first killing frost of autumn. The last substantial frost visited on May 1. We have nearly six months of frost free weather under our belts now. Astonishing! Forty years ago we were fortunate to tally three months and ten days without ice paying a call overnight. The rapidity of the change in temperatures over just a few decades has been breathtaking here in the cool corner of the world. And it will get hotter, far hotter, faster than advanced climate models had predicted even just five years ago.
On my nightstand is a book by scientist Peter Ward, entitled A New History of Life. In it he describes an ungodly warm night in a Cretaceous forest. The little mammals are out foraging, none bigger than a house cat. They own the night hours but are underground the moment the first rays of sun light the uppermost leaves high in the forest canopy. Yes, they fear the fleet and dagger-fanged dinosaurs and the pterosaur flying dragons. But the furry ones pale at the thought of venturing outside in the humid, ferocious daytime temperatures. Forced underground by the constrictions of their mammalian metabolism, they rest in the dark in their cool burrows waiting, waiting for the sun to set and the darkness return.
Caves offered humans their first true permanent homes out of the weather. Deep in caverns, the temperature was constant and far warmer than the Ice Age winters howling outside. From caves we humans ventured forth to conquer a planet. Perhaps, as the world’s climate grows too hot for our bodies to tolerate, when venturing out quickly brings about heat prostration and death, we will seek the sanctuary of caves once again. Only this time we will be in retreat, fleeing the intolerable heat of the day, the heat of our own making.
