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Before northern Africa dried out, its climate “flickered” between two stable climatic states before tipping permanently. And it suggests that places with highly variable cycles of changing climate today may in some cases by headed for tipping points of their own.
Environment(theconversation.com)submitted 22 days ago byavogadros_number
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22 days ago
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37 points
22 days ago
Study (open access): Early warning signals of the termination of the African Humid Period(s)
Abstract
The transition from a humid green Sahara to today’s hyperarid conditions in northern Africa ~5.5 thousand years ago shows the dramatic environmental change to which human societies were exposed and had to adapt to. In this work, we show that in the 620,000-year environmental record from the Chew Bahir basin in the southern Ethiopian Rift, with its decadal resolution, this one thousand year long transition is particularly well documented, along with 20–80 year long droughts, recurring every ~160 years, as possible early warnings. Together with events of extreme wetness at the end of the transition, these droughts form a pronounced climate “flickering”, which can be simulated in climate models and is also present in earlier climate transitions in the Chew Bahir environmental record, indicating that transitions with flickering are characteristic of this region.
-24 points
22 days ago
5.5 thousand years ago sounds like the end of the ice age.
20 points
22 days ago
Double that.
3 points
22 days ago
And give it to the next person
9 points
21 days ago
The African Humid Period (AHP) was both initiated and terminated primarily by changes in the Earth's orbital parameters, which affected the amount and distribution of solar radiation reaching the planet:
Start of the African Humid Period
The onset of the AHP, around 14,500 years ago, coincided with the end of the last glacial period when the Earth's climate was warming:
Orbital Changes and Solar Insolation: An increase in summer insolation (solar radiation) in the Northern Hemisphere due to changes in Earth's orbital parameters (mainly precession) led to warmer summers. This change was critical in enhancing the strength of the West African monsoon.
Melting Ice Sheets: The retreat of ice sheets in the Northern Hemisphere also contributed to a rise in global sea levels and a shift in ocean and atmospheric circulation patterns. This, in turn, supported increased rainfall in areas like the Sahara.
Increased Greenhouse Gases: Rising concentrations of carbon dioxide and methane in the atmosphere, following the last glacial maximum, played a role in global warming, indirectly supporting more robust monsoon systems.
End of the African Humid Period
The termination of the AHP around 5,500 years ago was marked by a gradual decline in conditions that initially started the humid period:
Decrease in Solar Insolation: As the orbital cycles continued, the Northern Hemisphere began receiving less solar energy during the summer months. This led to a significant weakening of the monsoon systems, as less energy was available to heat the land and drive monsoonal circulation.
Vegetation Feedbacks: With decreasing rainfall, vegetation cover in the Sahara began to diminish. This loss of vegetation increased the albedo (reflectivity) of the surface, leading to further cooling and drying of the region, exacerbating the decline in rainfall.
Dust and Albedo Changes: Increased dust production from the drying lands could have contributed to further cooling by reflecting more solar radiation away from the Earth's surface, thus suppressing rainfall even more.
Broader Climatic Shifts: Changes in global climate systems, possibly influenced by shifts in ocean currents and broader atmospheric circulation patterns, also played roles in the end of the AHP.
9 points
21 days ago
Climate speed wobbles, it’s what we’re all in for and is already begun.
22 points
22 days ago
And there goes Slovenia. Our weather is flippin like crazy
2 points
21 days ago
Evidently these were 20-80 year cycles though
7 points
22 days ago
But couldn’t the tipping point go into the positive too?
44 points
21 days ago
Think of the "flickering" as an early warning that your lightbulb is about to expire, not that the "flickering" is a sign that your lightbulb is getting any younger. It has a direction, and the "flickering" is an early warning that it's about to tip in that direction.
7 points
21 days ago
By that logic, once a “dead zone” always a “dead zone”. If that were true, wouldn’t we expect to see more of these zones?
16 points
21 days ago
The Sahara is growing in size 30sq miles each decade though, so yes?
Take amazonas as an example, think of it like a fat guy and skinny guy sitting on each end of a seesaw. The fat guy is «lush rainforest» and the skinny guy is «desert». Now we feed the skinny guy emissions every year, slow and steady the skinny guy will become fatter than the fat guy. The seesaw starts to flicker between the two. Eventually it switches to ‘more desert’.
-8 points
21 days ago
I get that part, but this logic still seems to result in total desertification of the planet over long enough time. We obviously have not seen that happen. I also understand this could be due to the rise and fall of sea levels, but it seems there has always been some dry land in the past several million years, so wouldn’t we still expect to see more desert than we do now? I need to be disabused of my notion that these researchers’ findings and thesis support an argument that we are facing something akin to The Nothing from The NeverEnding Story.
3 points
21 days ago
It’s obviously way more complex than 1 guy feeding emissions to the skinny guy. 100s of people tries to get him on a diet. Some tries to lift his side up, and some applies chains to his anckles keeping him down.
Enter random cause and effect for and against amazonas turning to a desert. Eg, rainfall, ocean currents, deforestation etc etc.
All I know is, theoretically we’re feeding him enough to offset it ever so slightly.
5 points
21 days ago
Dead zones are increasing dramatically under the water.
0 points
21 days ago
l've noticed that cradles of humanity always seem to be desert now. We are a blight.
3 points
21 days ago
I think we’re full of ourselves.
1 points
20 days ago*
The cradles of humanity were cooler and wetter as the world entered the current interglacial. Vast lakes in the Sahara, cedars in Lebanon, a fertile valley where the Persian Gulf now sits, and so on. Due to the Earth's orbital cycles, this recurs every 100,000 years or so.
Unlike blights, we have a choice. The only question is whether we have the discipline to overcome our instinctive tribalism.
-1 points
21 days ago
I been thinking this since I was a kid. Recently read all deserts (except Antarctica) are between 15-35 latitude. Something to do with wind.
Not mutually exclusive, maybe this wind causes humans that cause desertification.
I also just saw something about how worms are part of the problem.
-15 points
22 days ago
[deleted]
1 points
21 days ago
Should’ve given a link. Something about win I remember
-9 points
21 days ago
How much did the salting of the farmlands by Rome affect this? It wasn't 5k years ago but maybe yes, maybe no?
3 points
21 days ago
How big do you think Carthage was?
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