Guest essay by Susan Corwin
Agriculture started about 13,000 YAG when “it became possible”.
This is a continuation of the “top down” investigation of how civilization happened to develop.
.1.1 Answer is written in the dust: Ice Ages Were Very,Very Grim:
One need only look at the pictures from the “dust bowl” years of the 1930s in the mid part of the U.S. It brings to experience what happens when plants can’t grow. (eye candy deleted)
While that particular phenomena was caused by drought, the plants “died out”. Yes, trees, etc “survived” but they grew very, very, very slowly: like not being able to fertilize the crops on a farm, only this was due to lack of CO2.
The dust indicates that the world was pretty much a barren, empty place.
Homo Sapiens came out of Africa about 60,000 years ago.
.1.2 Living in a Dust Storm: the Genetic and Behavioral Bottleneck
For over 60,000 years, about 3000 generations, far longer than the time back to the stone age, the struggle to survive was huge.
=> likely, all species of land occupants were “endangered”: plants, animals, insects, etc.
Why are there few to no records, artifacts, etc?
=> There was “no one home”.
Why did early humans “come down from the trees?
= > a) they were hungry, and b) the trees were nearly dead.
Everyone was hungry all the time as there was little food to be had. Many children died and few able to survive. Families struggled to feed not just themselves, but their offspring. Family and (tiny) tribes were critical to defending any food found. Greed, bullying, and dominance had value. Grabbing resources successfully to feed “pregnant spouse and kids” was huge (if you are here).
I note that
=> the Neanderthals didn’t make it.
.2 Backup graphs/etc
.3 References:
Pulling links, etc from my notes, if you want more on the platter
there is this marvelous invention call “the computer” you might want to find out about.
- Lambert et al. 2012 EPICA Dome C Ice Core Dust Flux Data
- http://cdiac.ornl.gov/trends/co2/vostok.html
vostok.icecore.co2
- https://www.ncdc.noaa.gov/data-access/paleoclimatology-data/datasets/ice-core
- edc-co2-2008.txt
- ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/
- DomeC-800000-air_bubbles_historical.jpg
Carpe Diem: What you can envision, you can achieve!(sm)
© 2016 Susan Corwin, all rights reserved
We are here, it was survivable, conjecture, what is your point?
As for the “zone of plant death” starting at 160 PPM CO2, meaning nothing but deserts and dry soil and Earth becoming like Mars according to one chart above, and plants dying if CO2 drops below 190 PPM according to another: C4 plants can grow with CO2 down to 60-145 PPM depending on the plant, although one plant studied requires 150 PPM to complete its life cycle. C3 plants can grow with CO2 down to around 10 PPM. This is according to: http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.2010.03441.x/pdf
Oops, I said C4 when I meant to say C3 and vice versa. C4 plants can grow down to 10 PPM CO2.
You make an important point Donald: despite what the CO2 worshippers here have talked themselves into, a world with slightly lower atmospheric CO2 is not that bad really.
So flirting with measurable disaster is better than enjoying the proven benefits of CO2. And all for no proven climate benefits. You aren’t doing as well lately as you might think.
Unless you really need very high crop output to feed 7.5 billion people and growing.
Javier,
Yup. Six hundred ppm would be better than 400 and 800 to 1200 ppm best of all for C3 plants, which include the majority of crops and all trees.
And please do remind us what categories of plants comprise C4?
In the ice age paper by Ellis and Palmer, I propsed the same thing. But I suggested that dust production was mainly from high altitude regions in China and Mongolia. This is because the partial pressure of Co2 is naturally lower at high altitude, and because the dust in the Greenland ice core has been isotopically identified as comming from the Gobi desert .
(The Gobi is mostly steppe pasture at present, rather than desert. But during the LGM, it would have become a CO2 desert. Not an aridity desert, as moisture levels actually increased in many regions, but a CO2 desert.).
Modulation of Ice Ages via Dust and Albedo.
http://www.sciencedirect.com/science/article/pii/S1674987116300305
But it is difficult to get this message accross, as one reviewer blocked the paper by saying that CO2 has the same concentration at altitude as at sea level, and therefore plants would not be starved of CO2 at altitude. In return I asked him-her to go to the top of Mt Everest, and see if he-she was starved of oxygen or not. After all, the concentration of oxygen is the same on Mt Everest as at sea level….
Ralph
Evidence that this ice age modulation claim is correct, comes from the complete lack of ice sheets in the Asian northeast. So why did one of the the coldest regions on the planet not have an ice sheet? Answer – it was doo close to the Gobi, and received too much dust to allow ice sheets to form.
Ralph
Too much dust or too little precipitation. You really have no idea but you present your preferred explanation as the only possible one, and that is hardly scientific.
With the entire Arctic covered in permanent ice, where would the precipitations to build a huge ice sheet in North East Asia come from?
Dust is a symptom, not a cause. You have it backwards. Is like blaming the fever for the disease.
>>With the entire Arctic covered in permanent ice, where would the
>>precipitations to build a huge ice sheet in North East Asia come from?
The Pacific ocean has a clockwise rotation, pushing warm waters (and typhoons) up past Japan and beyond. So the Kamchatka peninsular is the wettest place in the Asian east, with rainfall at over 900 mm pa. There is plenty of moisture in the region now, and no reason to believe that there would have been insuficient during the LGM for ice sheets to form.
Ralph
The Kamchatka peninsula was covered in ice during the last glacial maximum, and you really have no idea how much precipitation there was in the North East parts of Asia that were not covered in permanent ice. So your idea that it was due to dust is simply a conjecture as it is not based on any evidence whatsoever. Do you distinguish between conjecture, hypothesis, and theory?
http://www.nature.com/ngeo/journal/v6/n10/images/ngeo1904-f1.jpg
You haven’t even checked your conjecture against Wikipedia. No a good symptom.
https://en.wikipedia.org/wiki/Last_Glacial_Maximum
Ralph, thank you for introducing the concept of CO2 desert. The implications are significant. I look forward to learning more about this.
So the arrival of humans caused the extinction of the megafauna! Everywhere? Are we now accepting that correlation is always evidence of causation?
I can and do accept that the arrival of modern humans on island land masses quickly kills off juicy turkey like flightless birds and their eggs as easy meals. But I am far less convinced that the same principle holds true of continental size land masses.
Anyway, didn’t the kangaroo survive the arrival of the first people in Australia? Or elephants in Africa and Asia, let alone lions and tigers.
We seem to be thinking in terms of people in vast numbers, but the reality is that humans barely survived the Toba event and the human populations credited with killing off the megafauna were on their own far too small to have achieved that result. And that’s before we get on to a consideration of their behavior. Early people don’t behave like crazed animal killers but rather like the first people in Australia live in relative harmony with the fauna around them. It makes no sense to go on an animal genocide murder spree if only because the effort required is too great.
I don’t dispute humans played a role in the extinctions, what I doubt is crediting the whole megafauna shebang to some kind of deranged behavior never observed or convincingly demonstrated amongst subsistence cultures. They were too busy surviving and the few thousand years between the emergence of people from Africa to the present day isn’t enough time to achieve the claimed result.
Does it not seem that blaming evil humans for everything to do with the megafauna extinction seem a slightly familiar refrain. Can you eat monitor lizards? Would you want to?
The evidence seems to point towards, ecological and environmental factors being the most important.
Monitor lizards have played a pretty big role in the diet of many indigenous peoples. Tastes like chicken.
I’m with you Moderately Cross of East Anglia. This theory doesn’t look plausible give the limited population of humans and their technology – sharp pieces of rock tied to sticks or poles. Even the plains Indians in North America possessing horses and modern firearms were unable to extirpate the bison. It took an organized, industrialized and deliberately focused effort by their enemies to all but accomplish that. This Arrival of Humans Led to Extinction Theory appears to be the environmentalist’s equivalent of Original Sin. Both are tenets of their respective faiths that proclaim the depravity of man and therefore impose guilt and the need for redemption and tithes.
Humans have demonstrated their ability to hunt species up to complete extinction multiple times. What you ignore is the amount of time they had at their disposal. We are talking about many thousands of years. We know that mammoths survived in small islands under less than ideal conditions until man arrived to those islands. Domestication was also a huge factor in extinction. Many domesticated species went extinct in the wild rather quickly after domestication. This is serious evidence that we were responsible.
Not every megafaunal extinction was due to man, but the evidence is pretty strong that man was responsible for driving a big part of megafauna to extinction. They were their preferred prey. They had few natural enemies if any, could be hunted easily by a band, and provided a lot more bang for the buck. The only continent were megafaunal extinction was moderate was Africa, our home continent. The megafauna there probably had time to adapt while we were developing our hunting skills over 2 million years.
Javier, a couple of points you make are what leads me to question the theory. One, the time frame of thousands of years that you mention would seem to make possible a variety of contributory causes beyond the mere presence of humans. Second your point about the survival of relict populations cuts two ways. The rarer a prey species becomes the more likely humans are to shift their focus to more numerous sources of protein. “Seen any mammoths in these parts, Ugar?” “Nope but look at all those rabbits. Hand me a rock. I’m hungry.” Mammoths trapped on an island with humans are going to get eaten to extinction. Vast herds in open territory are likely only be nibbled on by small bands following them. After a kill the humans will have to pause in their pursuit to process the carcass. While they’re hacking away the hide, slicing strips to dry over the smoky fire and butchering out the roast for the evening feast the herd moves on and the humans will have to pursue on foot; remember they ate all the horses. When it comes to the relationship of domestication to extinction what’s the motivation to wander the wilderness and slaughter something you’ve got penned up on the south forty or actually living in your tent.
Also not mentioned, people had domesticated dogs (wolfs) 15,000 to 30,000 years ago. A very potent hunting weapon. Others could have been the disease hypothesis and confirmed rat & fleas in later extinctions.
https://paleoecology.wordpress.com/2014/02/17/the-hyper-disease-hypothesis-did-humans-bring-about-doomsday-for-the-megafauna-of-the-pleistocene/
Mod,
The case for man-made extinctions not only on islands but continents is clear.
That some kangaroo species survived is not evidence that larger animals weren’t killed off by humans. They were, either directly or indirectly due to loss of prey species among predators.
In North America, bison, elk, deer, antelope, etc also survived, although in generally smaller forms. But the largest megafaunal species were wiped out, eg mammoths, mastodons, ground sloths, etc, and many of the medium sized, such as stag-elk, camels, llamas and horses. Others were extirpated in the Americas but survived in Eurasia.
Rate of reproduction is a factor as well as just amount of meat per kill.
On the contrary, Mr. Cross, the “buffalo jumps” (yes, I know they were really bison) in the North American west show subsistence hunters do behave like mink in a henhouse when opportunity permits.
(And what’s the difference a buffalo and a bison? You can’t wash your face in a buffalo.)
And yet the animals still survived so I don’t buy the human-caused extinction, except in a few rare cases where a population has become isolated, Dodo for example, or perhaps the mamoth.
Moderately Cross of East Anglia
December 27, 2016 at 2:57 am
Overkill isn’t deranged. Even when people recognize that a resource is limited, historically we have mined it out.
But paleo and archaic Americans didn’t think of megafauna as depletable. Hunters have as often as not been wasteful, not just in the Americas, but throughout the world.
One revolutionary aspect of pastoralism and agriculture is literally husbandry, ie husbanding resources.
Paleoamericans were no more depraved than Russian sea otter hunters who almost wiped out those winning creatures, the same people who did cause the extinction of Steller’s sea cows.
Which, if depraved, pales in comparison with Spanish conquistadors’ wiping out various Caribbean Indian tribes or British settlers murdering Aborigines. Or for that matter 20th century totalitarians targeting religious and ethnic minorities.
Moderately Cross said……..”Anyway, didn’t the kangaroo survive the arrival of the first people in Australia? Or elephants in Africa and Asia, let alone lions and tigers”.
Elephants, lions and tigers didn’t have to survive a “contact” with humans as they evolved alongside them and, in some cases, ate them. They didn’t have a real problem with humans until the Romans “needed’ them for their games. Current problems are due to humans with firearms.
Some kangaroos survived the arrival of humans in Australia but the big species didn’t. A lot of other large animals disappeared as well as the giant kangaroos e.., diprotodon, marsupial lion[drop bear], megalania…there’s a long list
http://www.abc.net.au/science/ozfossil/megafauna/fauna/fauna.htm
http://theconversation.com/hunting-or-climate-change-megafauna-extinction-debate-narrows-10602
The garden of eden/noble savage supporters desperately want evidence that climate change killed off the Australian mega-beasties. It’s unfortunate that their demise occurred around the time of human arrival.
A coincidence ?
The Noble Savage living in Harmony with the Natural World is one of those tropes found in literature rather than life. Look up “fire-stick agriculture” and recall that loss of (unmodified) habitat can do a species in just as effectively as eating it. What you get after >50,000 years of human occupation are the plants and animals that managed to survive human presence and practices.
I worked in Australia for several years and never did get to see a living wonambi or diprotodon…
Thank you Tony, but I still would prefer flightless bird. But of course the real point you make is that a species which is on the diet of indigenous people is still alive and kicking today. So why do we believe indigenous people in the ancient past killed off not only their food animals but virtually everything else as well. It just doesn’t make sense.
It makes perfect sense. It has happened in historical times. The instances are legion, from dodos to great auks, from aurochs to (almost) the American bison, saved at the last minute.
Passenger pigeons once darkened the skies in their millions. They were hunted to extinction while their hardwood forests were cut down for wood or cleared to grow corn.
Why is it hard to imagine people of 11,000 years ago doing the same?
Or consider the forests of Easter Island.
Chimp, that little phrase ‘historical times’ is part of the reason for doubting ancient extirpation. Historical time include methodology that was clearly unavailable to Paleolithic peoples, firearms, transportation, a market for the meat beyond a small group’s needs. By the way I believe the aurochs were a causality of WWI combat.
Old Guy,
The last recorded live aurochs, a cow, died in 1627 in the Jaktorów Forest, Poland, from natural causes. The causes of extinction were unrestricted hunting, a narrowing of habitat due to the development of farming, and diseases transmitted by domesticated cattle, and maybe interbreeding with the latter.
So if the claim that humanity, by way of CO2, has prevented the Earth from falling back into an ice age is true….
Having grown up close to arctic circle, the nuclear winter scare was more convincing at the time. After all my ancestors had narrowly escaped devastating famine caused by a year without summer in the watermelon optimum at the end of the 1800’s.
Agriculture was not discovered 13,000 years ago. It was between 10,000 and 5,000 depending on location.
Great graphic for illustrating ocean iron fertilization.
Dust contains iron which makes plankton grow. Plankton make clouds. Clouds make the planet cold.
Plankton also sequester CO2 in the sea bed. Lower CO2 means fewer plants and more dust, but also slower plankton growth. All readily visible in the records.
CO2’s influence on the climate is modest, highly non-linear and mostly through biological systems.
I enjoy the lack of agreement by paleo folks. It’s what makes for good science rather than the religious beliefs of the co2 believers. No problem for me with religion as long as we call it that and recognize that it is faith based.
Javier makes reasonable points but I’m not convinced that the extent of the megafauna extinction is explicable even with the thousands of years he mentions given the small numbers of people involved. Indeed the fact that African species did survive in the first continent modern humans occupied poses a big question mark against it being mostly down to humans. Just an Old Guy’s note about pointy spears and rocks is the issue. Doubtless dogs would prove useful once domesticated, but were they as widespread and more effective than wolves and other canine predators?
It would be interesting to make a list of which megafauna species we would credit our ancestors with driving to extinction. And why our ancestors wouldn’t have targeted the remainder. The domestication of some species may indeed have driven the wild varieties to the margins, but it might also have led to a loss of interest in the surviving originals by humans. Is the number of people sufficient to have caused continental wide extinctions ?
I think what I’m arguing against here is the casual assumption that we can explain all this by recourse to just one factor, e.g. Humans. I’m particularly against this as it plays into the modern green guilt agenda which paints humans as an unmitigated blight on the planet and, as stated by Just an Old guy, gets used to justify a whole package of other agendas. But I do agree with Jim G1, it is fascinating to discuss and one of the many reason WUWT is such a great website
Nobody argues that every megafaunal extinction was due to man. We know that the Dire Wolf became extinct in America before the arrival of mankind. The megafaunal extinction was clearly multi-factorial, but between those causes it is pretty clear that humans were one. And the important point is that the Megafaunal extinction took place in the Late Quaternary, essentially since 117,000 BP, and accelerated during a second wave that started around 40,000 BP.
So why did it not happened before during previous interglacials? Many species that went extinct were from hundreds of thousands to millions of years old. Why did they choose the Würm/Weichselian/Wisconsin glaciation out of many other glacial periods to go extinct en masse? What was different this time around? I think we all know the answer to that. What really distinguished this glacial from others was us. Early modern humans during the first phase of extinctions up to around 50,000 BP, and afterwards modern humans when extinctions really accelerated.
The extinctions did not diminish with the arrival of the Holocene, so it is tough to invoke climate change as the extinctions cover equally cold periods and warm periods. And it looks like most megafauna was safe in certain continents except for the occasional extinction, until modern men arrived there.
Some people try to build narratives to justify that it wasn’t us. However I think that the evidence is pretty clear that the emergence of an intelligent species has been poison to the planet from day one, and one of the first things we did was to prune our own tree to eliminate any competition as far low as we have been able to. We still have chimps, orangutans, and gorillas because they hide deep in the jungle, but I believe we will take care of that oversight in just a few decades. That we are exterminating the great apes that are no competition to us, and people still have doubts that we did the same with Neanderthals that were direct competition looks like an exercise in hypocrisy to me. We have changed very little in the last 40,000 years.
Javier self reveals much in the hoary misanthropic and self-loathing claim that man is an aberration of nature, a tragic fluke of evolution, a mistake of Gaia – that earth would be paradise but for the ascent of man. Ditch the self flagellation, I enjoy your factual reasoning much better.
Javier, you have made good points in the past. And you may be right about humans being responsible for extinguishing large animals. Or you may be wrong, and most probably you are partly right. But humans are a product of evolution too. We are not separate from nature, we are a part of it. This is neither good nor bad, it just is.
The evolution of intelligence and the ability to modify our physical environment in very substantial ways is a direct consequence of the (accidental?) formation of the first DNA molecule back in the Archean. It had to happen at some point, barring the elimination of life by a cosmic event. The present ice age provided the proximate stimulus for evolution of intelligence, but it presumably would have happened at some time anyway, during some future time of severe environmental stress. I suggest that you stop feeling guilty about it.
Humans have been orders of magnitude less poisonous for the planet than were the first photosynthetic organisms, which produced the Great Oxygenation Catastrophe over two billion years ago.
There is a large number of organisms which have benefited from the proliferation of humans. I regret as much as anyone the loss of the Pleistocene megafauna, but our advancing technology will permit some of them to be resurrected. Others, like Przewalski’s horse, can be bred back into survival.
And eventually, people will venture out into and colonize space, perhaps leaving some wild type humans back here on earth. Evolution will compensate for whatever life forms to which we have contributed to the demise. Until the sun makes the surface of our planet uninhabitable for complex organisms, extinctions will continue to be made up for, as after mass extinction events far worse than anything in the poor power of humans to effect.
African megafauna did better because they grew up along with evolving humans, so weren’t naive, as were Eurasian, Australian and American large animals.
In many cases, we have smoking guns, as with spear points in mammoths at kill sites and burned egg shells of giant Australian flightless birds. We also have the example of island extinctions following the arrival of humans. This includes Caribbean megafauna which would have died in the supposed impact event but in fact survived the YD, only to be wiped out thousands of years later. when people first landed on their island refuges.
I’m with Moderately Cross on this. We comment regularly on here that correlation does not equal causation. This extinction puzzle is no different. Much more likely that humans, their dogs, or other land bridge migrants brought diseases from Asia that decimated N.A. fauna. The mega fauna would have been more susceptible to extinction due to more limited numbers, perhaps exacerbated by additional hunting pressure. The evidence for the theory of human migration through the “ice free corridor” is nonexistent. The more recent theory is that they came along the ice edge by sea and infiltrated N.and S. America along the valleys of rivers. This makes infinitely more sense. Regardless, humans couldn’t have spread quickly enough to wipe out all these species.
On this point of extinctions, people have to take into account that the extinctions of megafauna occur where mans natural predator is absent …. i.e. Disease. Humans populations were more vulnerable in Africa, thus we had little impact. However , put us in a colder climate absent the plethora of diseases that plagued our ancestors in Africa, and we flourish at the expense of other populations. We simply outbred them, while using them for food. In Africa, this is not so.
I’m with Javier here. There are huge assumptions and generalisations being made in this article. Where do the data displayed on the graphs come from? Where are the locations of the data points?
The whole planet was allegedly dustier in the glacial? This conclusion is reached from the data at one specific location?
Maybe this post is a piss-take to show how people at WUWT jump on to a theory that is against the importance of CO2. I don’t believe CO2 is as important a control on climate as the IPCC think, but…..
Here are a couple of examples suggesting something different from this article. Along the south coast of Africa, hunter gatherers fished and ate seafood both in the last glacial and the previous glacial – Marean et al 2010 J Human evolution 59, 234.
http://in-africa.org/wp-content/uploads/2012/12/Marean-2010-JHE-pinnacle-point-flora-shellfish-and-modern-human-origins.pdf
So they survived, ate local seafood, no mention of different dust levels.
Neanderthals apparently existed until 39000 years ago, or possibly 28000 at least at a site near Gibraltar in Southern Spain. They may have co-existed with homo sapiens.
http://www.smithsonianmag.com/smart-news/neanderthal-carvings-gibraltar-cave-reveal-europes-oldest-known-artwork-180952581/
https://genographic.nationalgeographic.com/neanderthals-article/
OK, I know the last link is to National (sealevel rise inundates the statue of liberty) Geographic, but the dates are much later than the extinction date given in this article.
Those are just 2 points that quickly come to mind, which are contrary to the view raised here, without thinking what might come up if the hypothesis given here were properly dissected.
This needs a little editing. Although it may be correect that we came out of the trees due to poor tree growth, but it was several million years previously.
Susan wrote: “Agriculture started about 13,000 YAG when “it became possible”.
The graph immediately below show agriculture beginning after CO2 rose and shows that “agriculture worked” when CO2 rose to 250 ppm.
Nevertheless, agriculture began INDEPENDENTLY at different places around the earth AT DIFFERENT TIMES. CO2 rose to 250 ppm everywhere at the same time. The first signs of agriculture may have appeared 13,000 years ago, but it took many millennia to develop elsewhere in the world. Obviously, CO2 greater is not the ONLY factor that made development of agriculture possible. CO2 was greater than 250 ppm in previous interglacials. Why didn’t agriculture begin then?
Agriculture began in one location when CO2 rose to 250 ppm. It didn’t start in a dozen of other locations at the beginning of another dozen interglacials. Clearly a rise above 250 ppm had little to do with the beginning of agriculture.
The crops used in human agriculture are variants of wild plants with several mutations. It is generally believed that humans harvested such plants from the wild and – when they resided in one location for long enough – created conditions several key mutations useful to humans converged in one line. In other words, hunter-gathers unintentionally bred plant variants that made agriculture practical when they could survive while living mostly in one location, rather than constantly wandering.
The incorporation of CO2 into plant material is often the rate limiting step in the growth of plants. A 25 ppm rise in CO2, therefore could increase the rate of plant growth by 10%. It is doubtful that a 10% increase in growth rate is what made agriculture practical.
The most likely reason agriculture began in this particular interglacial is because a mutation that made speech more practical occurred during the last glacial period. With the ability to communicate better, humans were more likely to find it advantageous to live in small semi-permanent communities where mutations important to agriculture could be collected.
IMO, anatomically modern humans (AMHs) living during the Eemian Interglacial, c. 115 to 130 Ka, had verbal abilities comparable to their descendants today. They were however largely restricted to Africa, but did live in groups.
AMHs evolved around 200 Ka, however agriculture might not have developed during the Eemian, despite CO2 at about 330 ppm, because there wasn’t any need for it in the rich environment of the tropical and subtropical African homeland of AMHs.
A 25 ppm rise can make a large difference if the CO2 levels are at 200ppm.
From an older WUWT post
The IPCC WG1 AR5 Report discusses the CO2 fertilization effect on page 502. They estimate a greening of the Earth, due to warming and CO2, of 6%. This is at the low end of published estimates.
that was since 1980 or about 60ppm rise.
Agriculture in the Levant is thought to have arisen because of more seasonal weather being better for annual plants, about 9000 years ago. Figs were being farmed 11 500 years ago. Rice and millet farming started about the same time in China. The precursor to corn, teosinte, began to be cultivated 9000 years ago, about 1000 years after squash in the Americas.
Before the Holocene, it might have been still warm and wet in the tropics while the rest of the planet was cold, and people had started sort of farming with tubers and sugar cane in the tropics, most staples are farmed in areas with large seasonal changes. This might have been the bigger driver than CO2 levels.
We nearly became another Mars. And may yet!