The Earth can be divided into Land and Water Hemispheres. Six times in the past the Earth has had episodes of glaciation. The Pongola, Huronian, Cryogenian, Andean-Saharan, Karoo and our current Quarternary ice age. An ice age – an era in which the poles have permanent ice caps – is not the same as a glaciation, in which ice caps spread into lower latitudes.
The Quarternary ice age began 2.58 million years ago and it can be argued that it triggered the rise of our species, starting with Homo Erectus about two million years ago. The three part Becoming Human series is an excellent exploration of that process.
But there is a deeper story here … and one which I fear we have entirely missed. Look back at the timeline. The Oxygen Crisis is mentioned, one of five historical great extinction events. One of the others involved the Cretaceous Chixulub impact and another the Siberian Traps. The most mysterious is the Late Devonian – no asteroid, no continental sized lava flows … things just changed. One of the theories is that ocean chemistry changed due to the spread of vascular plants, which were better able to access soil nutrients. Massive changes due to plants aren’t unprecedented – the Carboniferous period resulted in massive coal beds, sixty million years worth before bacteria evolved to attack lignin.
So what are humans doing to the Earth? We know thanks to Antarctic ice cores that during the Quarternary has been breathing carbon dioxide in hundred thousand year cycles concurrent with the Earth’s orbital eccentricity. Our species evolved with 180ppm carbon dioxide minimums and 280 ppm maximums. Today we’re at 400ppm. We have no idea what is going to happen, but we’ve certainly interdicted the Quarternary ice age – continental glaciers will be gone in a century, Greenland is a millennia, and the Antarctic will inevitably follow.
The coasts where we all live will become uninhabitable. They’re going to drown. The tropics will be uninhabitable, they’re going to simply be too hot for our species. Our current bread baskets – U.S./Canadian, Russia, and Australian wheat country are already showing periodic failure. There are too many of us on this little rock and Mother Nature is going to take care of that problem directly.
The thing that we may have missed is something I brushed against in Dead Gods Of Atacama, now eight years in the past. Briefly, this world supports just a billion of us, unless we have access to fossil nitrogen, or we make nitrates from fossil fuels.
There has never been such as an efficient process for turning diatomic nitrogen into biologically available nitrogen as what we have done for the last century.
We make about 140 million tons of ammonia a year, the vast majority of which goes into fertilizer. The other sources of nitrogen fixation are lightning, which leads to five to twenty pounds per acre being deposited on Midwest farmlands, and nitrogen fixing bacteria that form relationships with some species of plants. Dividing 140 million tons by 20 pounds per acre means we’re producing the equivalent of what would accumulate on 14 billion acres, or 21.9 million square miles. Earth’s total land area is 57.5 million square miles.
Those numbers are only enough to provide the sense that there is likely a problem. This biologically available nitrate addiction is something we can step back from a bit – by becoming much more vegetarian as a species – but production will remain at a similar scope to what we are doing now as long as there isn’t a major population correction.
We already screwed up in terms of carbon dioxide and we’re running another massive experiment with nitrogen fixing that I’ve never seen discussed anywhere. Modern humans went through a genetic bottleneck due to the Toba eruption. So did Neanderthals, Denisovans, and Homo Floresiensis. Maybe in a thousand years the only humans left will be Denisovan influenced Tibetans living in a high, dry Himalayan plateau. Or maybe we’ll find our equivalent of what Wrangel island was to the mammoths, a redoubt somewhere in the Arctic circle where we make our final stand.