“Humans are tropical animals”, it’s said. Or are we? True, our ancestors did come from Africa (well…our homo sapiens ancestors, anyway), but seldom is it asked: what was Africa like for them? Consider that while the tropics are oppressively hot and humid now, we are in an interglacial period, a brief interlude between the real long-term normal of Earth’s climate that we’re genetically adapted for: a world 11 degrees Fahrenheit colder than today.
Most dramatically the ice sheets covered northern North America, northern Europe, as well as other places that are hospitable today, but seldom is it noted what the effects on the tropics were. Less pronounced, yes, but still noticeable. Most reconstructions of ice-age climate suggest that the tropics were perhaps 3-7 degrees cooler than today. The average site in the lowland tropics today perhaps is around 90 degrees Fahrenheit during the daytime with overnight lows in the 70s. Back then? It would have been more like mid to upper 80s during the day, with nighttime lows easily dipping into the 60s. Almost all of the world was drier back then, with correspondingly lower humidity.
Intriguingly, during the last glacial period somewhere like the lower Amazon would still have been hot and humid, but a more temperate sort of hot and humid that’s almost comfortable for human habitation, rather than the oppressive conditions that prevail today. Similar conditions would have prevailed in lowland Africa. Even the steambath that is Southeast Asia’s climate was no doubt noticeably less thick.
It gets even better when you realize that much of the tropics is not in the lowlands near sea level, but rather at altitude. Today somewhere like Brasilia is hot and humid, but noticeably less oppressive than the lower Amazon; located at 15 degrees south of the equator but 3700 feet above sea level, is consistently around 81 by day and 62 by night year-round. Back then? The days would have been 75 and the nights around 55 year-round, with less humidity and less rainfall than is the case today. Enough to tip much of the higher terrain in eastern Brazil out of the tropical climate zone altogether, and certainly enough to tip it from “hot and humid” to “comfortable year-round”.
If we viewed our world as our ancestors did in 20,000 BCE, then Brazil would stand out as being a very comfortable place to live.
Indeed, an enormous swath of South America would have had consistently pleasant weather, instead of the land of eternal spring being confined to a few refuges deep in the Andes. The vast rolling lowland around the Rio de la Plata, which today has a humid subtropical climate, was cooler and drier during the last glacial maximum. Buenos Aires is a humid 86 degrees during summer days now, but back then at its latitude summer days averaged perhaps 75 degrees, with winters being cooler but still mild enough, with days being around 50 degrees. With the drier air and the full sunshine that prevailed, pleasant conditions would have extended deep into the Pampas, though with Patagonia feeling much more like an extension of the Antarctic than the distinct entity it is today.
Nevertheless, that’s an enormous area of mild weather that would have prevailed year-round, easily exceeding the size of the entire United States. Microclimates? Dynamic, with variation in temperature by altitude easily noticeable, as opposed to being obscured by the hot humid steambath of the equatorial airmasses into different shades of “hot, hotter, hottest”.
This would have been even more true in Africa. Look at an elevation map and a huge area of southern Africa, roughly equaling the size of the United States, is high and dry even today, with subtropical climates extending a fair ways inward toward the tropics. Somewhere like Harare is at 17 degrees south of the equator, yet the 4900 feet of altitude moderate the climate, to the point where summer highs are only around 80 degrees, with nights dropping to around 60, winters averaging around 70 during the day, with nights being cool, 43 degrees.
As it is in our current interglacial, a large fraction of the ancestral human range in sub-Saharan Africa was in fact quite temperate, as opposed to tropical, but in the more usual glacial state of the Earth’s climate? This effect becomes much more pronounced.
Most reconstructions in the region find that summer highs in a place like Harare would drop to 75, lows down to 55, with winter highs dropping to the 60s, nights in the 30s, cold enough to be downright frosty much of the time. And once again, the climate that prevailed was dryer. Compared to California or even much of Europe, southern Africa back then might have been chilly. But the point is: the humid heat that prevails now even in a place like the Kalahari was just absent back then.
Even in the lowlands of southern Africa temperatures back then were quite clement in many cases; courtesy of ocean currents that flow unobstructed from Antarctica, Africa’s southwestern coast is already rather temperate. Luanda, located a mere 8 degrees from the equator, has winter afternoons that average 75 degrees Fahrenheit. Back then it was likely even cooler, with summers never reaching much above 80 degrees…a rather dry 80 degrees at that.
The Angolan Highlands, which today are one of the few refuges of truly pleasant climate in sub-Saharan Africa? Back then, they would have been downright chilly, with conditions more closely resembling today’s uplands of Bolivia than anywhere in Africa: cool and dry. Not quite as cold as the Antiplano; instead of 20s Fahrenheit during the night year-round these highlands of Africa would average 30s. But the point is that as you move southward, further away from the equator, higher latitude attenuates the effects of lower altitude, so the net effect is during the last glacial maximum there was likely a zone of essentially perfect temperate weather that extended not into just a few refugia in the mountains but across a very broad area of plateau, extending thousands of miles. Landscapes? Wide-open grasslands rather than today’s forests.
East Africa too tends to be high and dry even today, let alone back then, and like the Amazon even the Congo’s lower reaches would have been hot and humid but not oppressively so.
It’s often said that California’s weather, especially by the coast, is almost eerily pleasant for humans, being an environment where you can go outside in shirt-sleeves and be assured of being comfortable the vast majority of the year. And in general the Mediterranean climate zones are sometimes said to be ideal for human comfort. Which might seem strange, given humanity’s origins in the tropics…but consider that the Mediterranean climate zones today are the most similar area left to what the tropics were back then.
It gets even fancier when you consider the annual rainfall cycle in these lost tropical idylls. True, the subtropical highlands of our time tend to have monsoonal climates: dry winters and wet summers. Which is the opposite of the classic Mediterranean pattern of wet winters and dry summers…but consider that today’s monsoons in the tropics come courtesy of the intertropical convergence zone (the tropical rain belt), which in the last glacial maximum was greatly weakened compared to what we witness today.
Hurricane activity was also greatly suppressed back then; in the vast majority of the hurricane belts of today, sea surface temperatures were simply too cold for tropical cyclones to form at all. And those few that did form in the pockets of water still warm enough wouldn’t have lasted as long, in the face of greater wind shear and much greater dust levels — it’s been suggested that there was perhaps 20 times as much dust in the air globally as is the case now, no doubt related to the expansion of deserts and the decrease in rainfall. Hurricane and typhoon activity largely shut down; much greater swaths of the ocean would look like the south Atlantic or the southeastern Pacific: devoid of tropical cyclones.
On the flip side, storm tracks of mid-latitude extratropical cyclones swept much closer to the equator than is the case today; cold fronts would affect large swaths of the tropics, and these systems tend to arrive not in the summer but rather in the winter. These systems back then may well find their closest analogue today in the form of the famous “kona storms” of Hawaii, extratropical cyclones whose cold fronts affect the islands with some degree of regularity, despite the generally tropical climate at sea level. In the last glacial maximum kona-style systems likely regularly dominated the weather deep into the tropics on a global scale, rather than being isolated curiosities.
It’s thought also that subtropical high pressure systems, which are responsible for the seasonal drying out of places like California, were much stronger, which would further suppress precipitation in the summer months.
The net effect? Places like Brazil and Southern Africa would receive most of their rainfall in the cooler winter months, not in the warmer summer months…exactly as is the case in California and in the Mediterranean today. Places like Europe and California would see their role as the bastions of human climate comfort replaced by far larger swaths at more tropical latitudes in the southern hemisphere.
Though much of today’s mid-latitudes would still be contenders for human comfort. Consider that Europe and much of Asia back then was dominated by “the mammoth steppe”, which was frigid in the winter, but like today’s subarctic warmed up to pleasant conditions in the summer months. The same was the case in what’s now the southern United States, where the forests characteristic of the highest mountains of southern Appalachia now dominated the lowlands, which had a subarctic climate. Again, frigid in winter, but come summer? Pleasant. Indeed most of the northern hemisphere outside the immediate vicinity of the ice caps no doubt enjoyed pleasant weather in the summer months, along with sunny skies, dry conditions, and wide-open landscapes compared to the thick forests of today.
Visit Earth during the last glacial maximum in July and you’d actually find these northern mid-latitudes in their temperate flower, segueing via hot and humid but not oppressively so tropical lowlands into the vast belt of year-round temperate weather in the southern tropics and even some of the mid-latitudes. The total area with comfortable weather and stunning wide-open landscapes would be much larger than is the case today during our interglacial.
If you were viewing it with fresh eyes it might seem positively utopian…and perhaps, given our evolutionary past, that’s not a coincidence.
Ours is a world in ruins, suffocated by a hot humid blanket from apocalyptic global warming which has already occurred, even without us burning fossil fuels to make matters even worse. Perhaps what we truly yearn for when we stroll through the golden hills of California and feel at home is not California at all, nor even the Mediterranean, but a paradise lost in the ancient past…and which, someday, when the iceman takes back what is rightfully his, may return to welcome us back…
Ice Age Earth, by Ittiz of Wikipedia (CC-BY-SA 3.0), rotated by me
