Speculation, suggestion and mystery
Causes and effects of climate change
[Continued from The Vostok Ice Cores pt. 1: An Investigation]
Finding that atmospheric CO2 levels and surface temperatures on Earth (the average of which, according to this graph, seems to have quite regularly leveled off -regardless of partially more than tenfold higher than present carbon dioxide levels- at around 25 °C absolute, or 10-15 °C higher than today; which in itself is quite a lot) correlate during less than half of the observable time period of 500 million years, but do so very well under current and more recent conditions (i. e. with both values historically low, absolutely, and the relative difference to today near zero), it can be speculated as to why.
There are many possible factors, and it should help to eliminate those that are not recent and look for those that are.
There seems to be open dissent on which regions of the world are (and therefore were) most affected by climate change; and perhaps one should not so much focus on the direct effects of absolute temperatures, which are in dispute, but rather on the amount of heat or energy stored in the environment, which can be indirectly measured by the amount of ice in a region - where there is ice; atmospheric water vapor would be an indicator where there is not. These would, in either direction, buffer changes in temperature.
Then there are the oceans, absorbing and releasing carbon dioxide, dependent on temperature, and probably a host of other factors. Especially the thawing and freezing in the intermediate zones of this planet will have a direct effect on the amount of plant, and with that, animal life; both of these then have an effect on the amount of climate-affecting gases retained in the atmosphere.
In other words, global 'warming' or 'cooling' can take place without a rise or fall in temperature, but still affect all living systems; global thawing should not be confused with global warming. That will follow.
However, twice a year, the hemispheres of this planet alternately experience an externally induced short-term climate change, from winter to summer and back, where CO2 levels rise with the cold in winter (by about 20 ppm as far as can be discerned) due to the lower temperatures causing the levels of photosynthesis to diminish, and fall in summer due to the higher temperatures enhancing photosynthesis - the opposite of their long-term global behavior, where high levels of atmospheric carbon dioxide actually warm the planet through insulation; so there is something of a cause-and-effect negative feedback loop to look out for here.
The involvement of life
Solar energy may warm a planet directly, and atmospheric carbon dioxide insulate it; but if it has an active flora, its photosynthesis, by then reducing the amount of insulating carbon dioxide in the atmosphere, proceeds to cool it again indirectly.
So it could very well be that the interaction of terrestrial life - and, in other ways, marine life - with the atmosphere plays a possibly decisive role in flip-flopping the natural climate change cycles of the last 0.8 million years on this planet - and if so, before that as well - as all relevant factors are mutually interdependent. A few of these are:
- External forces and global factors: Atmospheric and surface temperatures depend on solar radiation, cosmic constellation, and atmospheric insulation, in which carbon gasses such as carbon dioxide (CO2) and methane (CH4) play a part.
- Absorption: The lower the overall temperature, the more of these carbon gasses are physically absorbed by land and sea; the higher the temperature, the more are (re-) released into the atmosphere.
- Biological activity: Atmospheric carbon gas levels are dependent on the amount of photosynthesis and decay taking place.
Photosynthesis, in turn, is dependent on both atmospheric temperatures and CO2 levels, as they are displayed by the Vostok ice cores.
Lower solar energy input, as an external cause, thus causes lower levels of biological photosynthesis, bringing on higher CO2 levels. This can be offset by higher levels of physical absorption or sequestration (i. e. condensation), which on their own (without regulating flora) could cause a runaway icebox (or, mutatis mutandis, greenhouse) effect.
But with stable or averaged energy input, planetary generated higher carbon dioxide levels bring on higher average temperatures, which in turn cause higher levels of photosynthesis; these, over time, would lower the CO2 levels again, resulting in both lower temperatures and lower photosynthetic activity. This is in accordance with the ice core data, and points away from changes in external energy input as a cause.
Also to be noted, the CO2 levels represented in the Vostok ice cores constitute an absolute measurement; the temperature measurement is a relative one. And if the requirement is for the trigger of a change, in a natural surrounding, to be sudden and global, it seems safer to choose a factor, that, like atmospheric carbon dioxide levels, tends to be more or less equal all over the world, while temperatures will differ wildly at any given time.
As always, even more factors not yet considered could also play a key role, such as the albedo, clouds, other carbon gases such as methane, and the smothering of life under a terrestrial sheet of ice; but it could very well be that all possible factors are bound into one decisive mechanism for a natural, cyclical, regular planetary climate flip, increasingly expressing itself in shape and impact over the past 0.8 or even 5 million years.
Searching for a mechanism
- one that involves atmospheric carbon dioxide levels (with the atmospheric and planetary surface temperatures)
The mechanism in to look for, quite likely biological in nature, would have to, over the past 5 million years and within the given terrestrial and extraterrestrial circumstances, have kept the global atmospheric temperature fluctuating between a set of two boundaries, enhancing their spread and edging closer toward, possibly, natural limits; flip- and flop suddenly upon touching one of these respective boundaries, either towards a sharp rise, or towards a slow decline; and, over time, become more distinct and develop ever greater momentum; either enhanced or unperturbed by sinking mean temperatures, perhaps even causing them.
Since most of this behavior has occurred over millennia without human interference, especially not through industrialization and the release of fossil carbons, the questions to answer seems to be:
- What happens naturally at an atmospheric CO2 level of around 180 ppm and a relatively cold surrounding, i. e. vast regions of comparatively low temperatures on a partially ice-covered planet?
- What happens naturally at an atmospheric CO2 level of around 290 ppm and mean temperatures slightly higher than today, in a relatively warm surrounding on a planet (almost) devoid of ice?
In regards to terrestrial photosynthesis, which seems to be the more volatile one concerning its dependency on atmospheric temperature and carbon dioxide levels, and therefore the more susceptible to these (and more determining!) than marine algae, there seem to be two major types of plants to account for most of the biomass, labeled C3 and C4, which process atmospheric carbon dioxide in a slightly different manner.
Of these, C3 plants, constituting almost all trees, posses the initial type of metabolism stemming from the primary evolution of terrestrial photosynthesis, which developed some 500 million years ago, in an atmosphere far richer in CO2 than today - over 2000 ppm at least, if not 4000 and beyond, and a global mean temperature of at least 23 °C, or 8 °C higher than today - not 2 or 3.
If these depictions are correct, then this development of terrestrial plant life was followed, about 200 million years later, by a sudden plunge towards more recent atmospheric CO2 levels and temperatures, at least this once; during the so-called Carboniferous period, in which present-day coal - one of the great masses of fossil fuels - was extracted from the atmosphere as carbon and deposited in the soil by vast forests of C3 plants, huge by today's standard, in which equally oversized dragonflies flew, with bodies 0.4 meters long and a wing span of 0.7 meters - the Meganeura; while the biggest flying insects in the tropics currently, by comparison, have wing spans of 0.3 meters and weigh probably far less.
Which brings us to an often overlooked factor: respiration and, even more so, flight - especially that of insects - is dependent on air pressure.
Windows of metabolism
Metabolism in general, especially that of 'cold-blooded' terrestrial animals, and respiration in particular, depends not only on the temperature and composition of the surrounding atmosphere, but on its sheer volume, height, and the resulting density and pressure - a volume that will have changed over time as well; and if the size of its dependent living creatures is to be a measure, it seems to have drastically diminished over the ages - begging the question if it is still diminishing, a prospect that is far more daunting than simple climate change - 'global suffocation' would be a real challenge.
All air-breathing and/or flying terrestrial animals have, with fluctuations and over time, grown generally smaller in size and warmer in body temperature (higher in metabolism) since their arrival around 500 - 400 million years ago; and so have terrestrial plants.
This could be significant. Perhaps aquatic animals were only then - in a denser atmosphere - able conquer dry land, because their breathing apparatus, that had evolved for water-borne oxygen, could handle air-borne oxygen at a greater atmospheric pressure than today, despite CO2 levels now considered detrimental, if not dangerous to fauna - and afterwards grow to preposterous size.
Much later, warm-bloodedness, high metabolism rates, fur and feathers may have developed in response not so much to sinking overall temperatures, but greater extremes - which could be have been due to sinking air pressure: compare Archaeopteryx, one of the first feathered bird-like creatures, the size of a pigeon, with the flying reptiles of the times, with wingspans of 10 meters and a body weight of 200 kilograms.
If one of these could be cloned today, it would most probably be unable to leave the ground, while asphyxiating on insufficiently sized lungs. All dinosaurs would have that problem; and that of starvation - especially the herbivores.
The point is not that, once upon a time, plants and animals were bigger than they are today; the point is that they are now smaller than they once were. Even mountains may have been higher in a higher and denser atmosphere, due to raised erosion levels, as it seems to be no pure coincidence that their highest peaks now hardly protrude out of the troposphere. There are no...
Why is should this be significant?
A simple increase of atmospheric oxygen through enhanced photosynthetics might alleviate the problem of respiration, but it would not relieve the weight/flight problem - while causing spontaneous forest fires, to reduce the oxygen level below a specific threshold again, which at the momentary air pressure is around 21% or 210,000 ppm - as compared to a relatively low average of 210 ppm CO2.
As every decarbonized CO2 molecule results in one free molecule of O2, the effect of reducing carbon dioxide emissions (and/or enhancing photosynthesis) will have little effect on the levels of atmospheric oxygen (and sequestered carbon) at this moment - due to the fact that there is currently very little atmospheric carbon dioxide to draw from in the first place.
On the other hand, re- releasing large amounts of carbon dioxide deposited in carbonate rock into the atmosphere again, would indeed raise the air pressure - while facilitating photosynthesis, enhancing plant size, raising the mean temperature, changing the amount of water vapor, etc.; filtering out more ultraviolet light rays - an effect which would in itself massively change the living conditions not only of terrestrial fauna, but of flora as well; many plants, especially primordial ones, are extremely sensitive to certain solar ultraviolet light emissions, which causes them to evolve to small, hardy sizes in clear mountain air while growing large in warm, foggy valleys or on cloudy hills.
Small differences in air density can have big consequences, as a visit to the dead sea will show.
While the primordial C3 plants evolved in a distant period of high atmospheric CO2 levels and temperatures, C4 plants are a more recent, if ubiquitous development; for some reason, they evolved some 35 million years ago, and can cope with less favorable circumstances, such as even higher temperatures, arid conditions, and low carbon dioxide levels; and if these graphs are to be believed, their development coincided with the most recent dip towards low levels of both atmospheric carbon dioxide and mean global temperatures.
It is also said that C4 plants "became significant" around 6 to 7 million years ago, which contains the time frame of 5 million years to the present already under discussion here.
C3 vs. C4 metabolism
The overall impression is that the C4 metabolism, mostly present in plants such as weeds, grass etc., but in very few trees, is the more recent, more robust development, while the older C3 plants - such as trees - have a higher metabolic performance at high carbon dioxide levels. As experience shows, and does the Carboniferous period, they work quite well under colder conditions as well. This, too, may be significant.
Publicly available graphs comparing the C3 and C4 metabolism, as this one taken from here, are not completely consistent in their depictions; but it seems safe to assume that, all in all, higher CO2 levels benefit forests, while lower CO2 levels benefit grasslands:
- C4 plantations, i. e. open grasslands, metabolize very low atmospheric CO2 levels, according to some presentations almost down to zero; and even 180 ppm or 0.018% is quite close to 0, compared to former levels of 2000 ppm and more.
- C3 plantations, i. e. forests, stop metabolizing at atmospheric CO2 levels below 180 ppm, but surpass C4 plants regularly at higher atmospheric levels of CO2 - somewhere beyond 500 or 750 ppm - as the photosynthetic performance of C4 plants begins to level off, somewhere around 350 ppm, while that of the C3 plants continues to accelerate.
From this comparison, it seems possible that, at atmospheric carbon dioxide levels of around 290 ppm, or even before, a certain set of plants, namely those of the C3 type - i. e. trees - would naturally begin to take over from those of the C4 type - i. e. shrubbery and open grasslands; and that atmospheric temperatures alone would not bring this about.
As atmospheric CO2 levels are quite similar world wide, this would happen almost simultaneously on a planetary scale, and that even before the point where their metabolism factually overtakes that of their rivals for light, space and water; it could happen at that point where their disadvantage in metabolism becomes insubstantial enough for them to close the canopy, thus blocking out the light for smaller plants; from which point on they actively keep their advantage.
This active behavior crucially distinguishes the outcome of a biological mechanism from that of an inorganic chemical or physical equilibrium. And as trees also are passively not as easily consumed as grasslands, this further enhances their relative advantage - and with it, their carbon retention.
If left undisturbed, forests, which, according to one definition, still cover approximately 30 % of the world's land area, would naturally take over large swaths of currently agriculturally held land, including grasslands, which in turn are said to now cover up to 40 % of the world's land area in comparison.
And they would do so even under pre-industrial atmospheric CO2 levels of 280 or 290 ppm, the recent atmospheric level of this current interglacial peak; and though higher temperatures may benefit both types of plant, higher CO2 levels and temperatures, simply put, would seem to benefit trees over grass.
IF therefore the global temperatures are indeed driven by atmospheric carbon dioxide levels, as is assumed, then the corresponding oscillation of atmospheric temperatures and CO2 levels takes place between the defining CO2 levels of
- 180 ppm, at which point photosynthesis, especially that of the C3 type, practically comes to a halt, killing off all trees; which abruptly raises atmospheric CO2 levels, thus sparking a new, rapidly warming 10,000 year era of initially C4 plant growth, finally resulting in CO2 levels of
- 290 ppm, around which point C3 type trees of greater biomass begin to take over, and subsequently deplete the atmosphere of CO2 again; thus cooling the surface of the planet over the following 90,000 years, until self-induced suffocation levels of atmospheric CO2 are reached once again and their canopies re-open for a new cycle.
Of course, all plants bind carbon only for as long as they live, unless they contribute to long-time deposits such as peat or topsoil - or coal.
It is therefore difficult to estimate the biomass, or carbon fixation, involved in the comparison; but C3 plants - i. e. trees - are said to make up "90% of terrestrials plants", while on the other hand C4 plants - i. e. grass - constitute "5% of the biomass but fixate 23% of CO2" - however that may be possible - unless, of course, they are eaten, or burnt, before they have a chance to deposit themselves as carbon residue.
It is estimated that a global topsoil gain of around 0.5% a year would be enough to bind the annual CO2 emissions worldwide - which actually would be quite a lot, if calculations are correct, that carbonized topsoils naturally form at a rate of millimeters per century, or thereabouts.
But then, in 90,000 years… the magic of big numbers.
And there we have it
A public internet search for anyone that may have connected the minimum carbon dioxide level for floral metabolism as a possible trigger for climate change, reveals: Yes! A certain Allan M. R. MacRae did so, registered on July 1, 2017 at 1:04 pm; and as it seems, his original insight even then reached back to 2009.
If the absorption would be purely physical or chemical, the depletion of the planet's atmosphere of CO2 would not regularly rebound sharply at 180 ppm, but instead level off at some equilibrium, asymptotically approximate to zero or show some irregular behavior driven by volcanic eruptions and the like; decisively, not much would stop CO2 levels from falling below the levels needed to sustain terrestrial flora - and, luckily for ourselves as terrestrial fauna, this does not happen.
Biological systems, in contrast, tend not to level out, but to fluctuate between specific minima and maxima. In more detail, the suggested scenario of photosynthesis-driven periodic natural climate change could perhaps be described in this way:
- During a 10,000 year fast warming period, initially, robust grasses, insensitive to low CO2 levels - while supporting large herds of grazing animals - will follow the receding ice shields, which in turn set free CO2 from biomass buried in the hitherto covered soil. The rising atmospheric CO2 levels then raise the global temperature still further through insulation, setting a potentially runaway positive feedback scenario.
- But the world-wide rise of carbon dioxide levels, at some point, causes the grasslands to give way to trees; which, in a relatively short time, will out-perform and smother them, while actively depositing carbon (back) into the soil. And at the height of an interglacial peak, like at this very time in history, at atmospheric CO2 levels around 290 ppm and a mean polar temperature of 2- 3 °C above current values (or so it was for the last 400,000 years), the planetary system will swing into cooling mode.
- For, once enough terrestrial areas capable of releasing CO2 into the atmosphere are again covered with trees, the forests, with their high metabolism and deposition rates, due to longer life span and less susceptibility to predation, while simultaneously reducing wildlife, slowly begin depleting the atmosphere of carbon; as global temperatures fall in consequence, ice shields grow again and insulate large areas of terrestrial biomass from exchanging with the atmosphere.
- This cooling phase lasts around 90,000 years or more, during which the global atmospheric CO2 level is run down to a minimum of 180 ppm, and the mean polar atmospheric temperature down to 8- 9 °C lower than at present, at which point almost all terrestrial photosynthesis grinds to a halt. All forests die globally, not of low temperatures, but of self-starvation or asphyxiation; thus ceasing the carbon dioxide depletion of the atmosphere.
- With that, the stranglehold that (terrestrial) plants had on the CO2 levels of the Earth's atmosphere is suddenly released, the canopies of the forests open, and in those areas not covered by ice, sunlight reaches the soil again, undemanding grasslands proliferate, and atmospheric CO2 levels rise sharply as the system goes into the next warming phase: the bottom trigger of a glacial trough has been activated.
- With the atmospheric greenhouse back in function again, the short-termed metabolism of the newly spawned grasslands - where not only buffaloes roam and graze, but mammoths did too, immediately re-releasing their carbon back into the atmosphere - and the high rate of decay from formerly buried biomass cause atmospheric CO2 levels and temperatures to spike, typically within 10,000 years, in an interglacial positive feedback loop, which would then, at atmospheric CO2 levels of around 290 ppm, lead to the glacial positive feedback loop of the next cooling phase: the top trigger of the interglacial peak.
Now, should turn it out to be that atmospheric carbon dioxide levels do not raise or lower the surface temperature of the planet, or not enough, there is still the phenomenon that grasslands - which in this scenario precede the forests - tend to be hotter than these; if this is an illusion due only to shade, or if they do indeed convert more latent solar thermal energy into potential chemical energy, thus temporarily taking it out of the active equation, and what role the thermal and carbon reservoir of the hitherto ignored oceans play in this scenario, remains to be understood; the fact however that trees cannot survive atmospheric carbon dioxide levels below 180 ppm seems undisputed.
Although the exact mechanism for the abruptness of these triggers is still not clear, this scenario would be consistent with all the phenomena described up to now, as well as with the resulting negative saw tooth curve, which, rising sharply and falling slowly, would mirror that of a living system periodically overusing its resources - in this case, terrestrial photosynthesis regularly depleting the atmosphere of CO2; which, all other conditions remaining the same, it would do on a regular basis in roughly the same time intervals, while, as a living function, it carves out the edges of its possibilities.
The so mirrored regular saw tooth (or 'Seneca') curve, a slow rise followed by a sudden drop, can be seen as a 'life' curve; it seems that all organic systems tend to actively go beyond their optimum or equilibrium - which it seems also they cannot discern on principle - and strive for a maximum, thus regularly overfeeding on their resources and suffocating on their waste, and subsequently go into a steep decline.
And of course, the fauna, including humans, will follow the flora down the food chain; and, by the way, so will sea levels in a slow 100,000 year ebb and tide of 120 meters. This is the reason why the currently submerged continental shelves have been swept so clean; this is the ninth time in a million years that the sea has come and gone in slow tides lasting 10,000 years and even slower ebbs lasting 90,000.
At the moment, we have high tide. There could be more to come, but not too much.
Which brings us to the final point:
The current 'stable climate' anomaly
Within the time frame of the last 0.8 million years, we are currently in the latest observable 'climate peak', and should, in the natural course of climate change, right now be teetering on the brink of a tipping point into the next 90,000 year long cooling period towards the next ice age.
In other words:
Even with the knowledge of today, thousands of years ago, no-one would have given much about a hundred ppm or so of atmospheric carbon dioxide more or less, or a few degrees of difference in temperature over a couple of centuries; and quite rationally so, as it would have been within the expected range of the Earth's climatic behavior.
It is just that we are, right now, at a natural maximum tipping point; and the system is not tipping - yet.
Indeed we are very lucky - and it may be that luck has nothing to do with it, but that we are historically able to discuss these things precisely because we are where we are - that we find ourselves right now at the end of a natural warming period, and should therefore be in the unique position to answer the following critical question:
- IF global climate change is driven by atmospheric CO2 levels, and these are in any way influenced by terrestrial photosynthetics,
- how has the terrestrial flora, or anything else, changed in the past 10,000 years to warrant an imminent and sudden tip into a decline of both atmospheric carbon dioxide levels and subsequent global temperatures?
And we cannot answer it.
For, if one looks closely at the current interglacial period, it hasn't.
In fact, the Vostok ice core graphs show a current anomaly of 10,000 years of "climate stability".
To illustrate, a sample of graphs depicting the temperatures and carbon dioxide levels for the recent 10,000 years:
For easier and direct comparison:
Temperature: https://archive.thinkprogress.org/uploads/2013/03/0pF9B4lrrd_amLhH_.jpg taken from https://thinkprogress.org/
Carbon dioxide: https://static.skepticalscience.com/images/co2_10000_years.gif taken from https://skepticalscience.com
And for the 500 million year comparison once more:
In the last 10,000 years, global temperatures, as measured in the Antarctic, have uncoupled themselves from the continuously rising CO2 levels and more or less stayed level.
- While atmospheric carbon dioxide levels continued to rise, by about 14% in total, namely 15 ppm of the 110 ppm in total, from 265 to 280 ppm,
- which is perfectly in sync with the pattern of the last 400,000, or even 800,000 years, but still 10 ppm below the maximum of the last four interglacial peaks,
- the global temperature has leveled out, and seems to have begun to drop, even before the normal temperature maximum of the last four interglacial peaks of at least +2 °C more has even been reached;
- apart from both values being too low, they have also become disconnected -
- such an uncoupling has happened before during the period in question, but not during a peak.
So, compared with its predecessors, this time around, natural global warming is not only too little, but too late:
The +2 °C in temperature and the 10 ppm difference in atmospheric CO2 still missing to the usual maximum of 290 ppm of even before "the industrial revolution hit", i. e. before humans began to mine and burn carbon fuels, is not a question of missing time.
On the contrary:
The current recovery from the past ice age has taken almost twice the time as usual.
This effect is 2- 3 times greater regarding the temperature than the CO2 levels; the naturally oscillating system should have run past its peak now, and return colder temperatures than it presently does.
For the last 10,000 years, temperatures have somehow been prevented to follow CO2 levels, and have missed the usual mean by 2- 3 °C.
So if this currently is an anomaly, what has uniquely happened in the last 10,000 years to alter the normal process of natural climate change?
Well, one new factor that comes to mind in global history during the last 10,000 years and before is the global arrival of modern man, from stone age to industrialization. Could that have been it?
Lever must (not) pass this point
[To ye who do not know: Invoking the Beano Bash Street Kids right there]
Every system has a point beyond which it may not be pushed for too long, by penalty of irrevocable destruction; and it seem as if eons of low atmospheric carbon dioxide levels have allowed a fallback, or comeback, mechanism to evolve, precisely for when the system hits reserve in that respect.
The Eurasian cave paintings of grazing animals are some 40,000 - 15,000 years old, that time when humans crossed the ice bridge from Asia to the Americas; their last continent to conquer. These paintings utilized soot and charcoal, showing that the use of fire was not unknown to the artists.
Their depictions include the woolly mammoth - a species that survived all eight interglacial warming peaks during the last 800,000 years, the more recent of these displaying a mean global temperature 2- 3 degrees higher than the current one - and went extinct precisely at the beginning of the current peak, which has now been protracted for 10,000 years; at which time humans began replacing their hunting and gathering with herding and farming, possibly for having wiped out most of their prey on the previously emerging post-glacial grasslands.
- Could this 'global climate standstill' of the last 10,000 years be the result of an actual ancient and ongoing anthropogenic climate change, giving the impression of a natural temperature plateau, and deflecting from its threatening natural decline?
- Is man therefore the agent not of climate change, but of climate standstill? Do we want the climate to stay exactly as it happens to be now, perhaps to stop our own natural evolution?
- Could humans have possibly been 'jamming' the upper climate change trigger for all this time, influencing the climate in the last 10,000 years by turning from hunting to farming - much more than through their industrialization in the last 200?
- And if humans had let nature run its course, as in the times before, would we then already be back to our current normal, but 10,000 years further down the road to the next ice age?
- And what happens (or doesn't happen) if we keep this up?
Speculation on the possibilities
What humans do, all over the world (apart from wiping out wildlife by chasing herds of, say, woolly mammoth over a cliff somewhere in Siberia and then later blaming their mass extinction on 'sudden global warming'), and always have done, is slashing and burning down forests and generally keeping the area open, for grazing and farming, housing, cooking and heating; a human behavior which began to emerge globally, just around the time when naturally risen CO2 levels would have enabled trees to reforest the world, and possibly usher in the next ice age.
Even in the stone age, humans, few as they were, used impressive amounts of wood; and much of it for building, especially in the challenging climates of Eurasia.
Now, IF humans did indeed prevent forests from naturally taking over the grasslands and sequestering carbon, how big could their impact possibly have been, given their overall low numbers at the time?
Furthermore, and this seems to be in total contrast to the general idea, this anthropogenic deforestation, if so, seems to have kept the planet from heating up by keeping the plains open - despite rising CO2 levels. And this would be very strange indeed. But, as previously stated, such divergent developments have taken place before, under circumstances yet to be studied.
Of course, if grasslands and agricultural areas are kept open for human benefit, and worse, consumption, then CO2 levels may indeed remain high and continue to rise, as carbon is not deposited terrestrially; but man-made or not, the true mechanism of stabilizing the global temperature 2- 3 degrees below its natural maximum for 10,000 years, despite rising CO2 levels, remains a mystery.
What remains, too, is the uncanny feeling that we might be witnessing ourselves in a Darwinian, meaning unconscious, evolutionary interaction with our environment for these past 10,000 years:
Whatever humans were doing, on a world-wide scale, that, unbeknownst to them, influenced the global temperature, this was to their benefit; had it not been, they would not have continued with it.
So could it be, that what is instinctively fueling this idea that temperatures should not rise higher than exact the 2- 3 °C more which it should have naturally reached 10,000 years ago, to naturally tip the system - that we subconciously know we have cut down the regulating, biomass-depositing, long-term planet-cooling forests?
Have we been unconsciously regulating the planetary climate to our advantage by preventing it to slip into a new ice age - far before industrialization?
How high would atmospheric CO2 levels have risen without industrialization, and at what point, if at all, would natural global reforestation have thrown humans out of the game once more?
Or is all of this speculation wrong and futile, as global temperatures are primarily influenced by cosmic cycles, after all?
This other possibility - as ever based on the premise that the Vostok ice core data is depicted correctly in public, and is relevant - would mean that, just by chance, humans have hit it lucky with the first time ever event of a 10,000 year interglacial climate stability in the last of the past 800,000 years, right after their first global arrival as homo sapiens in the last ice age before, and have used this period of unusual temperature stability to begin civilisation by farming and herding.
This would be possible; but it would still not give the reason why global temperatures suddenly stayed level during 10,000 years of rising atmospheric CO2 levels after following (or indeed, leading) them closely in every interglacial peak before.
Of course, any drop or even a stabilization of a fairly low planetary surface temperature can cause atmospheric CO2 levels to rise by keeping the level of photosynthesis low, as happens every winter - but what then caused the temperatures to stay level so unprecedentedly - quite apart from the fact that they are at a relative peak?
So, could there in any way have been a human role in the proceedings this time around for the current interglacial peak?
And/Or did perhaps humans (or rather their predecessors), like the woolly mammoths, survive the previous three un-meddled, and therefore hotter, interglacial peaks only because these were so short and snappy - just to stay in the narrative?