Saturday, July 15, 2017
HUMANS AS AN ICE AGE SPECIES II
15 July 2017
Scientists have recorded five significant ice ages throughout the Earth’s history: the Huronian (2.4-2.1 billion years ago), Cryogenian (850-635 million years ago), Andean-Saharan (460-430 mya), Karoo (360-260 mya) and Quaternary (2.6 mya-present). Approximately a dozen major glaciations have occurred over the past 1 million years, the largest of which peaked 650,000 years ago and lasted for 50,000 years. The most recent glaciation period, often known simply as the “Ice Age,” reached peak conditions some 18,000 years ago before giving way to the interglacial Holocene epoch 11,700 years ago.
That humans arose during an ice age may be due to chance, but over the last 750 million years, the chances of a species emerging in an ice age (global mean temperature ~12C) would have been roughly 5%, as the planet is hot (~22C) something like 80% of the time. (Mammals showed up 220m years ago in the late Triassic, one of many warm/hot periods.)
Obviously species have had successes against longer odds than that. However, my working hypothesis is that there is more ecological diversity during ice ages (though not snowball earth of 650m years ago). If the earth usually has palm trees and crocodiles in the arctic circle, then there would be a lot less maple, walnut and apple trees elsewhere. This is not to say that humans did not originate in the tropics, as it seems we did, and there is a lot about the transition from forest to savanna that I don't know much about. Also, the African drought-induced near-extinction was apparently overcome by moving to the seashore, which gets you into the aquatic ape and ecosystem boundary hypotheses.
Keep in mind that the planet was 2-3 C colder then than it is now, and a bit more than half the difference is pre-industrial (most sea level rise has been/will be preindustrial). I think it's clear on the 750m year chart that we have been in a warming phase since we became tool and technology users, at the very least. So global warming was already happening, though I think it's obvious that this is the first time in geological history that fossil carbon has been burned. Thus, this cycle can go (and obviously is going) faster and possibly higher than in the past. Other causes of climatic variation include fluctuations in solar intensity, atmospheric clarity and orbital variations (Milankovitch), but the big cycle seems to be carbon-driven, which in my view is the strongest single argument that humans putting carbon into the atmosphere is changing things (that is, accelerating an existing trend). In fact, it is bluntly an irrefutable argument if you study geological history.
One can also see that at least 8 degrees C of the big fluctuations happen very quickly (less than 1 million years) in geological terms. I honestly believe (1) that if we don't get smarter, we'll move from 15 to 22C in only a few hundred years (a new geological record), as that will put all the carbon there is into the atmosphere, but also (2) given a few hundred years, we will get much smarter and actually more or less totally eliminate carbon burning, or at least highly restrict it, and that much sooner than that, we'll have the technologies to capture carbon and take it back out of the atmosphere (no UN bureaucracy or carbon credit system needed, because we'll be rich enough that we can easily afford it).
Note that around 13-14C is where the bigger/faster moves usually happen anyway, as that is enough to get the positive feedbacks going with methane, forest fires, tectonic rebalancing, etc. That is, whatever the bureaucrats may think, we've been past the breakaway threshhold for some time already.
So let's just say that humans had tried to get their start at 22C, which would take you roughly to 35m years ago. There would have been no coral reefs, the entire equatorial region would have been uninhabitable (>120F), and there would have been only tropical and desert ecosystems. I'm pretty sure it would have been a less diverse world, which is not to say that tropical systems are not diverse.
It is probably also not accidental that we are post Cretaceous-Paleogene extinction creatures (66ma), as the meteor impact that extinguished 75% of earth's life forms occurred at the height of the last warm period, which also (perhaps meaningfully) marked the rise of mammals, though it was still very hot for another 40m+ years after the mass extinction (there is also a current mass extinction being driven by human modification of all planetary ecosystems). The meteor impact at 66ma doesn't even show up on the longterm climatic cycle chart, but it would have been very cold for a very short time, geologically.
Importantly, humans didn't show up, even our precursors (who emerged no more than 6m years ago), until temperatures dipped down to ice age levels. However, Haplorrhini (apes, monkeys, tarsiers) are a human precursor who showed up immediately post extinction event (63ma), so maybe that is also meaningful.
Finally, the real advances in human technology have occurred in only the last few thousand years, which has been a period of significant glacial retreat (warming with positive feedbacks engaged long before industry started). I have just refreshed myself on Lake Agassiz, which oversat Kenora, Ontario (where I live) as well as most of central Canada and the North Central US. Interestingly, the central North American glaciers melted for thousands of years without sea level rise, because the lake was held back by a glacial dam that first broke about 13,000 years ago, then reformed, and had its last break about 8000 years ago (both events raised sea levels several feet, and one or both may account for the multicultural flood narratives).
The rupturing of Lake Agassiz is linked to the rise of systematized agricultural in Europe which enabled the rise of cities, and that is also dependent on the Atlantic Meridional Overturning Circulation (AMOC), which sustains moderate European temperatures, but which has reduced 30% since 1957, associated with increased warming-induced freshwater flows into the Arctic Ocean, and thus with southward flows into the Atlantic (conversely, the Arctic Ocean is shrinking due to warm water penetration further north). On a positive note, when the AMOC reduces, we have fewer Atlantic hurricanes. On the downside, Europe would turn much colder very quickly if the circulation turns southwards (it currently forks, and half flows north around Europe, and half flows towards West Africa.
As to unanswered questions, human have obviously benefited by the plummeting of global temperatures to their lowest historic levels perhaps 6-8 million years ago, but we have also capitalized on the bounceback to warmer temperatures, which coincides with hominid evolution over the last 2-1/2 million years. In brief, it appears that humans thrive when ecosystems are multiple and diverse, and my best guess is that the Quaternary Ice Age created the exact types of increasing diversity on which emerging humans eventually capitalized.