I think it was in Michael Palin's show Sahara, he's talking to some locals living in a village in the middle of the desert, and while I'm wondering why anyone would ever settle out there, the person being interviewed relayed that many more people used to live there before it became a desert. It wasn't that they moved out there, they were all that was left. Kind of post-apocalyptic.
Edit: found the mention, he's talking to folks from the dogon tribe in mali, @29min - 30min says that the area was heavily forested 500 years ago. The location is the bandiagara escarpment, old cliff dwellings . All the episode of Sahara are on youtube, I highly recommend the series.
The Earth's precession cycles driving Sahara rainfall have a period of about 23,000 years. Whatever caused deforestation there over the past 500 years likely was distinct from the Green Sahara cycles.
Great reminder to all that we know we are effectively killing Lake Chad, but there's not much anyone is really doing about it.
Timbuktu’s population dropped by 4/5ths since the Middle Ages, from a near legendary city to a nearly forgotten one.
Pretty amazing clip, sent me down a rabbit hole. I can't help but think what extreme climate niches our descendants 500 years from now might be surviving in, that were once fertile & lush.
Models help test test our understanding of past events. If you can create a model that reproduces past events, there is a chance that you have understood something about those events. Equally, however, there is a chance that you have created a model that only coincidentally works, because you forced it to do so.
When "scientific" articles write that a model "confirms" some conclusion, they are just wrong. Given enough free variables, you can construct a model that does anything you want. Models confirm nothing.
"The results confirm the North African Humid Periods occurred every 21,000 years"
No, they don't. Did the Sahara green every 21000 years? except when there were ice sheets? Only physical tests can confirm that. Do these greening phases correspond with orbital precession? Statistics can confirm that correlation. Running a model can test hypotheses of causality, but it doesn't "confirm" anything, least of all physical facts.
It's like how the model for a snow slab doesn't prove there was a snow slab that slipped over the Dyatlov Pass tent that night, despite what the media claimed about the case being solved. It only shows that it could have, assuming the data and assumptions are correct for that specific location.
Or models showing some solution to the Fermi Paradox, and proponents claiming that the mystery is finally solved. How do they know the model is accurate?
I'm not a historian, archeologist, or any sort of relevant expert.
But I've long had the pet theory that the Green Sahara is the origin of the Eden Myth.
Homo Sapiens origin, lush vegetation, turns to dessert for some reason beyond our comprehension...
I've always interpreted the Eden myth as a memory of the development of agriculture.
Before agriculture, people lived as hunters and (mainly) gatherers. The life of a Hunter-gatherer is, surprisingly, mostly leisure, because of the abundance of food and the low population density. Even Kalahari Bushmen, who had been forced to live in the dessert, were found to average only about 1 1/2 to 2 1/2 hours of productive labor a day in a study .
In the bible, God's punishment is :
“Cursed is the ground because of you;
through painful toil you will eat food from it
all the days of your life.
It will produce thorns and thistles for you,
and you will eat the plants of the field.
By the sweat of your brow
you will eat your food
until you return to the ground,
since from it you were taken;
for dust you are
and to dust you will return.”
 Stone Age Economics by Marshall Sahlins (https://archive.org/details/StoneAgeEconomics_201611)
Think it was a different green area - the Fertile Crescent, not the Sahara. Eden would have been where modern day Kuwait is. As for ancient towns in Sahara, for a long time people wondered how the desert people lived in such a harsh area - but it turns out they've just been there since it was lush. They didn't move to the desert and learn how to survive there, they're just what's left of those populations from the Sahara, and adapted to the changing conditions.
I dunno, I mean the myth doesn't say "Then The Lord Smote the Garden Unto Sand", it says that Eden (and the plants) persisted in the same spot as before... Humans were just being actively blocked by an angel with a flaming sword.
I think the general consensus is Mesopotamia that at that time was a lush green area. The myths after all probably originate from the city of UR.
It obviously doesn't cover the why of Sahara's greening, but for anyone who has access to BBC iPlayer, the following programme  has a nice summary of humanity's journey out of Africa.
It's amazing that the majority of the world's population is descended from the couple of hundred individuals that left during one of these greening periods.
or without iplayer https://yandex.ru/video/preview/13243013351978795119
This is an interesting video I came across awhile back: https://www.youtube.com/watch?v=jjOW6kLEckg
Apparently Libya has a huge ancient aquifer (or several aquifers really) that they built pipelines to access, and now that's their main source of fresh water.
The aquifers, being left over from a previous era when Libya got a lot of rain, are not being refilled by anything.
Surprised there's no mention of Sahara Pump Theory in this article.
It’s my understanding that the Amazon is dependent on minerals from the Sahara blowing across the ocean, and if we “re-greened” the Sahara, the Amazon would be negatively affected.
Is this the case, and if so, does that mean the Amazon is only as old as the desert version of the Sahara?
Edit: bit of an answer here for anyone curious: https://earthscience.stackexchange.com/questions/2566/what-w...
I've heard about some efforts to regreen the desert by careful planting and geoforming. Anyone know anything about this? It would be cool if it could work, even partially.
You might as well be referring to permaculture generally. It’s exactly about careful, intentional planting and working with the environment rather than trying to tame it.
Geoff Lawton’s Greening the Desert Project comes to mind in particular: https://www.greeningthedesertproject.org/
You might find histories of Fresno County, California interesting.
When settlers showed up, it was essentially river running through a desert landscape. They dug canals to support agriculture and the landscape greened up substantially.
A lot of water law and patented water development tech happened in Fresno County. It's essentially a modern "hanging gardens of Babylon" situation and no one seems to talk about it.
Darwin and Hooker did something like this in the 19th century to Ascension Island. Few know this. Deliberate modification of an ecosystem couldn't be done lawfully in the US. However, that's an administrative obstacle rather than a technical one.
I think the key is the lack of water.
In the Sahara and the Middle East, which are sunny and warm, if you add water plants grow fast.
We can imagine future scenarios in which fusion or solar are used to power large-scale desalination and irrigation to represent deserts from the coasts.
They did a bit in China and there is talk of doing the Sinai https://www.theguardian.com/environment/2021/mar/20/our-bigg...
Check out the work being done by https://justdiggit.org/
There are projects going on in both China and on the African continent. Search for "Great Green Wall".
> The results confirm the North African Humid Periods occurred every 21,000 years and were determined by changes in Earth's orbital precession. This caused warmer summers in the Northern Hemisphere, which intensified the strength of the West African Monsoon system and increased Saharan precipitation, resulting in the spread of savannah-type vegetation across the desert.
So… as we finally exit the current ice age we should expect a green Sahara?
> So… as we finally exit the current ice age ...
If by "Ice Age" you mean period of glaciation - the most recent one ended ~ 11,500 years ago after starting some 120,000 years ago.
We're not currently in an "Ice Age" .. although by general expectation of this cycle we should be slowly moving into one . . . save for this recent rapid rise in C02 and atmospheric insulation increase caused by the most recent century of accelerated human activity.
See the enlarged graphic from the Nature article this thread is about:
or the full original paper:
> ... we should expect a green Sahara?
Well, as noted we've rather changed the system parameters a fair bit, it's difficult to know what to expect where anymore other than a general increase in the amount of trapped energy at the lowest sea | land layers globally.
It's enough energy to eventually tip the otherwise periodically stable climate cells into all manner of not seen before new redistributions of climate activity.
When was this research established? I've heard about this a few years ago but when was it found that Arabia was green historically?
Periodic desertfication of the broad north African region north of the Sahel
is a notion that dates back to at least the early 1980s (and probably decades before) and is based on layering in river systems and other strata evidence.
This specific research tightens up the timing and driving factors for the specific Sahara region (Libya, Egypt, Sudan) and doesn't relate to the Arabian Peninsula which is an almost seperate landmass more than three quarters surrounded by sea water.
On that landmass the Arabia Felix region (modern Yeman (mostly)) is known to have been greener in the past.
So with the co2 forcing function, is it possible that Canada be glaciated again And that the Sahara be green?
That would fly in the face of conventional thinking which is that Canada will be temperate and the Sahara will be more arid.
The article is saying that the green Sahara coincides with periods of greater seasonal rainfall and humidity, caused by changes to the procession of the Earth and the effect that has on the seasons. It's possible that current anthropogenic climate change could make the Sahara greener, but it's also possible that it might not. In any case, the greening would probably take hundreds of years or more to happen.
Somewhat off topic, but if anyone's read Sand County Almanac by Aldo Leopold, he talks about how the American Southwest, specifically Arizona, used to be green. Apparently the familiar reddish brown resulted from human impact
I went to school in Socorro, NM which was very brown on a dry year and pretty green on a wet year and my understanding is that it was a pretty grassland before white folks showed up but overgrazing caused the creosote bush to move in.
If you go up the hills to the plains of San Augustin where the VLA radio telescope that is around 7000 feet in elevation and I think a bit cooler and wetter and that is a very pretty grassland where you see big herds of antelope grazing and you might think you were in Africa.
What’s the proposed mechanism for that? It doesn’t seem plausible to me on the surface.
Carbon emissions ACCELERATED climate change. Climate change is natural. It's the ACCELERATED change that is the problem. Not enough time for species to adjust.
Even natural climate changes can be problematic, such as drier climates precipitating the fall of the Roman empire or the late bronze age collapse.
Carbon emissions are moving the climate into a mode it would not have entered without human intervention.
Your argument is similar to “Everyone would have died anyway; this thermonuclear winter just sped it up. Totally not humanity’s fault we live in a bunker.”
Meteor strikes are also natural. That doesn’t mean they are desirable.
Sahara could be green again in the future once the East African Rift becomes a new ocean 10 million years from now.
Would it though? The trade winds converge over central Africa, which is already quite lush, so presumably any extra moisture would just be deposited there instead of a few thousand miles to the north.
I was mistaken in saying "the middle of the desert", the area of mali being toured is decidedly on the edge of the desert.
Same story for the Aral sea. https://en.m.wikipedia.org/wiki/Aral_Sea
How exactly are "we" killing Lake Chad and what would be an easy solution to save it? Also, who is "we"?
Humans. How do you want me to segment us to minimize the problem?
And we are killing it by diverting water from it.
Any recommended sources to learn more about it?
The Fall of Civilization series:
The Songhai Empire - Africa's Age of Gold https://www.youtube.com/watch?v=GfUT6LhBBYs
Paul MM Cooper's podcasts and video essays on YT are excellent. There's info on Mansa Musa in this episode: https://www.youtube.com/watch?v=GfUT6LhBBYs
Not of Timbuktu specifically. There are books on the history of West Africa, or Mansa Musa.
Because the only thing you can ever have is a theory. The strongest theory is the one that gets chosen. Theories vary in strength over time.
Nothing is ever solved or proven. Theories get stronger and stronger evidence. Believing in a theory doesn't in any way help you make sense of the world. We just do it for expediency of communication.
Theories being ultimately all we have, there is (or should be) no “chosen” one. People are free to believe whatever—this is a pre-requisite for theories to evolve.
There may be a theory that enjoys better predictive success for a while, but if everyone always believed in a singular “chosen” theory then we’d get nowhere: to evolve a better theory, you have to come up with and believe in something other than the preexisting one. Thus, it is normal for multiple theories to coexist at any given time.
Crucially, a theory is all map no territory, always and necessarily. It describes something we do not understand in terms of something that we do understand. At its core, it is a metaphor—and more than one metaphor can be useful, each in a slightly different context.
> Because the only thing you can ever have is a theory.
Here's mine: there is a "correct" set of theories (or truths) that the universe adheres to, we're just nowhere close to even guessing at them yet. But current theories can be closer or farther to them
I've always thought that being cast out of Eden was not so much a punishment, as merely an unavoidable consequence: having eaten from the tree of knowledge, we now also have the ability to appreciate suffering, and thus no longer experience paradise. That would make paradise a state of mind, rather than a place.
After eating the fruit God lists a number of consequences, which sounds somewhat like a punishment, but that could just as easily be interpreted as "well, I didn't want this to happen to you, but now that you got to this point, you'll have to deal with the following". That includes increased pain in giving birth (a consequence of having larger brains), and the rise of agriculture. Eve is also only named after eating the fruit, not before.
The snake gets cursed for what it did, and so does the ground, but not Man. God even goes so far to provide them with clothes, and acknowledges their growth.
The tree of knowledge of good and evil is basically just the spark of consciousness. Humans are unique in our ability to consciously foresee and plan for the future.
On the one hand, that's a blessing because we've made tons of progress towards alleviating objective suffering and scarcity.
On the other hand, it's a curse, because we always have to be aware of the impending inevitability of our death. We can't ever completely live in peace and paradise ever again, because we have become conscious of our existence and the context our life experience exists within.
Would it be better to not have gained that spark of consciousness and live the paradise of ignorance as animals in the wildreness? Lives at peace except for occasional bursts of pain and terror.
The snake always seemed to me to be a Promethean figure in this story. It brought us knowledge, like Prometheus brought us fire, and got punished for it by a god.
That's about camels eating cactus.
I do not struggle to see echoes of an oral tradition recalling receding greenery. I can quite imagine a cult feeling expelled from Eden as the productive grasslands walked away.
Hey, that's Aziraphale! Good guy.
> Many people, meeting Aziraphale for the first time, formed three impressions: that he was English, that he was intelligent, and that he was gayer than a treeful of monkeys on nitrous oxide.
Water bunds are particularly effective:
(That site breaks the url bar though; I had to get that via a search engine. Wtf.)
China has gone through various tries of this for the last couple of decades. The first tries failed horribly because of lack of water and they sent the wrong trees to be planted for the ecology they were going into. I'm not sure how their current try is going, we will just have to see when/if the dust storms stop coming in the spring.
We are still in an ice age, just an interglacial part of it: https://en.wikipedia.org/wiki/Interglacial, https://en.wikipedia.org/wiki/Ice_age
Let's not play the dull game of pedantic definitions.
The GP to whom I replied referred to the ~ 21 Kyear glaciation cycles associated with humidity changes in the Sahara, I specifically asked about what they meant by "ice age" and pointed out that now other parameters have been altered (the insulative properties of the atmosphere) we can't reliably predict how specific regions will change in the future on the basis of the past.
Your own link clearly differentiaties between geological "Ice Age" (Quaternary glaciation of the past 2.5 million years) and the popular notion of "Ice Age" (glacial cycles during that time).
Hence why I carefully wrote:
> If by "Ice Age" you mean ..
Do by all means contribute to the discussion, that is so much better than just playing the game of "gotcha's" (or whatever it is you're doing in your comment above).
> Earth is currently in the ice age called Quaternary glaciation.
Basic definition is when ice covers both poles
Does anyone know where one can find the estimated size per year of the Sahara. All I kind find are reductionist crap like it’s 10% bigger now than 1920. But this does not say if it’s in a growing or shrinking trend just that it’s bigger now than then. Was it even bigger in 2000? And now shrinking from a top or has it been a gradual increase?
Considering that there are archaeological sites in the American Southwest that are posited to have been abandoned due to the disappearance of their water supply, it is hard to blame all the aridness on “white folks”. Moreover, when I cycled through the Anza-Borego State Park in California, several of the information boards discussed how hardscrabble the existence of the Native American peoples in this area was, because it was already very much desert and required special strategies to survive.
This is a solid point. I was at Mesa Verde, the national park with the cliff dwellings. Apparently the people who lived there just up and left, well before Columbus showed up on the other side of the continent. One theory is that the current Hopi people are their descendants.
It's pretty clear that bad things happen, even when white people aren't around.
I don’t know about Arizona, but apparently, parts of the great plains were dense forest that Europeans clear cut, and they simply never recovered. Also, California used to be green in the summer, but then people introduced non-native grass that grows rapidly in spring, choking out the native plants, but dies by July. It is the reason the hills are so yellow and dusty and dry.
There is some stuff along route 66 that suggests the desert was there longer than humans though. One example is the crater they used for moon landing training. It’s basically undisturbed, and is extremely old.
The Great Plains have been grassland since the LGM, that’s one thing you can’t pin on European settlers. East of the Mississippi though, a squirrel in the 17th century could have walked from Maine to Georgia and back without ever touching land.
Or The Samalas eruption - which is believed to have caused the Little Ice Age - and killed 90% of Europeans & North Americans at the time (55M people).
I imagine many millions of large mammals and birds and insects also died.
See also the Year Without Summer, 1816.
Apparently Frankenstein and Dracula were both born that 'summer' at one of Byron's gatherings. Something to pass the time indoors.
> and killed 90% of Europeans & North Americans at the time (55M people).
That’s very far fetched.
> which is believed
By whom? The little ice age peaked in the 1600s.
The meteor isn’t the problem. It’s the delta-V of the meteor which is the problem.
Speed and size. But as speed generally is high (11-72 km/s)  then size matters more. Anything hitting you at km/s that survives the journey through the atmosphere is going to hurt I think. :)
Probably yes, but I’d need to see a model to be sure. Changes to the general circulation of the oceans had massive effects on paleoclimates. Recent examples are the closing of the Panama strait, and the opening of a new strait between Australia and Antarctica.
Segmenting maximizes rather than minimizes.
When the problem is caused by all humans in the world, then no one feels pressured to do anything.
If you could instead name people individually, they would have to take a stand to actually do something about the issue.
Why would they have to take a stand? Ah because other people would make them take a stand. Why would these other people make the first group of people take a stand? Because they care. What if they don't care? Somebody else should pressure them into caring so they can pressure the ones who can do something about it. Etc etc
My point is that this is what it's usually meant by "we are not doing anything about it". It generally means that there is not enough collective awareness about an issue for the people involved to have enough incentives to do the right thing.
Some people observe that the issue is under somebody else's direct responsibility but draw the conclusion that the responsibility chain ends there.
Other people instead think it's their responsibility to apply some sort of pressure from outside and failure to even attempt to do so extends the responsibility of the inaction to them too.
Some of those people extend their feeling of responsibility to also shame people for not shaming other people.
This is all natural and human and as with all human things it functions well until it fails catastrophically
There is no need to believe a theory, but when it comes time to make an irreversible choice; you better pick the strongest theory. No belief necessary. Sometimes you do have to choose, and you have to accept that your choice will have a degree of uncertainty.
The point is that there is no “strongest” theory. Different theories are different maps. There is no perfect map, at that point it is no longer a map but territory.
Better not use a bad map, but there can be more than one good map depending on what you need it for.
The chosen explanation should be held to be contingent and corrigible but that doesn’t mean all explanations should be held to the same regard particularly when some can be harmful as well as contradictory.
"Harm" is essentially circular logic. Assuming we are acting logically, the only harmful theory is a wrong one. And so when speaking of harm, you are assuming the correctness or incorrectness of some theory. This is why having a free and open society where any theory can be comfortably pursued to its natural limits is absolutely critical. Everything should be being constantly challenged to ensure that we aren't just falling into a new dogmatic cycle, as history shows we ultimately always do.
Beyond this I'd also add that many 'rock solid' theories do contradict each other. The obvious example being relativity and quantum mechanics which have mutually exclusive things to say on countless topics ranging from black holes to the nature of time itself. Both work phenomenally well and have abundant evidence in their own bubbles, but side by side - they can't both be true in their current state.
It is not abnormal for multiple theories or hypotheses to contradict each other. In strictly natural sciences it is usually possible to experimentally rule out some of them, but not always so (for example, sometimes the technology is not there). In philosophy it is often not the case (no experimental means available where concepts like “objective reality” are involved).
Thats why should use electricity to free all camels from the servitude of the desert plains.
I’m actually asking the question — when we leave the ice age, will the Sahara turn green? Presumably, based on this paper, the sea water will rise and then yes it will get more rain.
It's not really a "theory" as anyone normal uses that term. We know beyond any reasonable doubt that there's significant genetic, cultural, and political ancestry tying modern Puebloan groups to the the people who inhabited Mesa Verde (and other earlier pueblos). "Most" went east to the Rio Grande area, but plenty went west too. Some Hopi ancestry also comes from other groups to the north, west and south (into modern Mexico) where Puebloan groups no longer exist.
With that said, Spanish and American colonization of the Southwest has radically changed the landscape. Much of what's now low brush used to be substantially more vegetated, similar to organ pipe national monument. Mesquite was rare outside intentional cultivation. It's actually an invasive species from the separate Chihuahuan deserts in Texas that was spread alongside cattle. Another fun fact is that prior to colonization, no part of AZ+NM was more than a day's walk from water (~20mi), which was important to long distance travel and later the Apache wars. That's no longer true due to groundwater depletion.
Do you have a citation on mesquite spreading from Texas with cattle? I ask because the aforementioned information boards in the Anza-Borrego State Park speak of the local Native American population consuming mesquite, and Wikipedia, too, says the same about those Cahuilla people of southern California. From what I gather, it is only certain species that have later been invasive?
To be fair, North America used to have a lot of megafauna like wooly mammoths and they were hunted to extinction by "native Americans" when they showed up via the land bridge at Alaska.
> The eruption may have helped trigger the Little Ice Age, a centuries-long cold period during the last thousand years.
> In a 2012 paper, Miller et al. link the Little Ice Age to an "unusual 50-year-long episode with four large sulfur-rich explosive eruptions, each with global sulfate loading >60 Tg" and notes that "large changes in solar irradiance are not required."
> The elimination of nearly 55 million, or 90 per cent, of Indigenous people in the Americas during European colonization led to global climate change and the “Little Ice Age” of the 17th century, a recent study finds.
In fairness, the Samalas Eruption did not directly lead to Ghengis Khan or Black Death. But during the Little Ice Age - the populations reduced by ~90%.
> the populations reduced by ~90%.
Specifically in the Americas, not the whole world. Also I don’t see how climate change was the cause.
European population had already recovered to its pre black death peak by the 1400s and had significantly surpassed it by 1500 (78 vs 90 million).
"Assuming we are acting logically"... which a lot/most/all of people don't at any given time which is largely the issue at hand.
I can't think of any examples where this is the case currently. A historic example would be genetics. There's little doubt that
genetics influence near to every aspect of our competencies. And that's extremely useful information that can help improve life and society in countless ways. It only became harmful when a man decided to take it to an illogical extreme, predictably creating a very real dystopia in his fanciful efforts to create a very distant utopia.
For sure but that should change how much regard we hold them in right? The example given by your sibling comment is a great one because we know that there is something we're missing in the explanations given by General Relativity and Quantum Mechanics and that's okay. It doesn't mean that neither are useful just that we understand their explanatory limits. In comparison flat-earth theory is basically completely contradictory to vast swathes of evidence and explanations.
Flat Earth is more of a sign of protest masquerading as a theory rather than an actual theory. It appears to be more focused on finding elaborate ways to deny other theories rather than seeking truth. It is inelegant, illogical, and cannot be stated without involving a host of conspiracies of low probability. (The fact that one can only adopt it given values/traits/issues that let one seriously believe in those conspiracies may also make it useful for social signaling.)
What I find tragic is that STEM-inclined crowd might have sort of triggered that defensive reaction by supplanting religion directly with natural sciences. Sometimes when you point out something similar to this thread (that physics does not make statements of absolute truth, there are only models of which none can be fully provably correct and complete, etc.) you encounter vicious insistence that the world is literally the way it is described in physics textbooks or Wikipedia—and it will stay that way until we are blessed with a new explanation for how things really are. You can notice how to a religious person this might feel indistinguishable to a competing religion, rather than an orthogonal aspect of worldview (it is completely possible to be both religious and a natural scientist).
Come to think about it, even your comment sounds slightly off to me in this way, primarily due to the mention of “explanatory limits”. I would prefer another term (possibly “predictive limits”). Again, “explanatory limits” makes it sound as if GR or QM (or X or Y) is capable of “explaining” something. Taking a model, just one metaphor that fits how some aspect of apparent reality behaves in response to input or another observation, and using that metaphor to explain how things are in some objective sense (which is what I take “explanatory” means) is, to me, a misuse of the model. The fact that the model works for some of our purposes makes it useful, but does not grant it explanatory powers.
I wish more of us techies resisted the urge to see in natural sciences explanatory powers that they do not possess, and instead branched a bit into philosophy—which can actually provide some grounds for meaningful discussions on topics that are out of scope of natural sciences per se. (As a side-effect, this might also make us more understanding and bearable to talk to for someone on a different bandwagon than ourselves.)
Checking back this was somewhat of a subspecies thing, but indigenous people were also cultivating mesquites outside their native ranges for food.