The once-green Sahara turned to desert over thousands of years rather than in an abrupt shift as previously believed, according to a study on Thursday that may help understanding of future climate changes. And there are now signs of a tiny shift back towards greener conditions in parts of the Sahara, apparently because of global warming, said the lead author of the report about the desert’s history published in the journal Science. The findings, about one of the biggest environmental shifts of the past 10,000 years, challenge past belief based on evidence in marine sediments that a far quicker change created the world’s biggest hot desert.
Reuters: Sahara dried out slowly, not abruptly: study
Science: Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years
Abstract:
Desiccation of the Sahara since the middle Holocene has eradicated all but a few natural archives recording its transition from a “green Sahara” to the present hyperarid desert. Our continuous 6000-year paleoenvironmental reconstruction from northern Chad shows progressive drying of the regional terrestrial ecosystem in response to weakening insolation forcing of the African monsoon and abrupt hydrological change in the local aquatic ecosystem controlled by site-specific thresholds. Strong reductions in tropical trees and then Sahelian grassland cover allowed large-scale dust mobilization from 4300 calendar years before the present (cal yr B.P.). Today’s desert ecosystem and regional wind regime were established around 2700 cal yr B.P. This gradual rather than abrupt termination of the African Humid Period in the eastern Sahara suggests a relatively weak biogeophysical feedback on climate.
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
“there are now signs of a tiny shift back towards greener conditions in parts of the Sahara, apparently because of global warming”
Uh, guys, the dessication was due to…cooling?
Guess the sentence was included to ensure publication and continued funding.
Or just more ANTHROPOGENIC influence
New Scientist 29 March 2008 reports:
“Returning to Africa after a 10 year absence, Chris Reij could barely believe his eyes. On the arid margins of the Sahara in Niger, all he could see were trees. It was no mirage: after studying land use in Africa for three decades, he was witnessing the untold story of the re-greening of the Sahel.”
“I went to a village called Dan Saga, which I knew when it had virtually no trees. Now it had 80 to 100 trees per hectare. On the way back to the capital we drove north into the Tahoua region. In 1994, most of this area was bare plateau. Now you couldn’t see the villages because they were hidden behind trees. I saw the same thing everywhere. What was emerging was nothing short of a miracle. I reckon Niger has gained 200 million trees in two decades.”
“After long deliberation, they agreed that the only way to survive was to protect the young trees that grew spontaneously on their land. A few years later, the trees protected their crops against the winds and stopped the sands spreading. The trees are now part of their farming system, providing fodder for livestock so farmers get more manure for their fields. We have also found that in areas with trees, fewer adults leave the villages to find work elsewhere. Trees are creating more local economic opportunities”
There is now discussion between African governments and the European Union about creating a “green wall” of trees across the Sahara from Senegal to Djibouti. It has been suggested that large amounts of trees might encourage more rainfall downwind and trees reduce wind run evaporation.
Hey if they could get some carbon credits they could even get some extra value out of the trees.
Dear Editor,
How can I post an article on your website?
I have a story on French nuclear policy as a role model for Australia.
Regards
Fred
Luke, the greatest anthropogenic influence on the Sahara over many centuries was having people traversing it with camels and goats.
When Afghans and their camels were brought to Australia from around 1840 to open up transport routes, all the trees dissappeared along these routes and in many cases have not returned.
200 camels carrying 400 woolpacks were capable of consuming 200 trees per night in that fragile environment.
The Ghans did introduce the date palm though to some of those remote wells for which I was often thankful.
Fred – “I have a story on French nuclear policy as a role model for Australia.”
Can’t wait for that one – please post it Jen – we have not had a good nuclear brawl for weeks.
along I went we watched reminded
Hey Ender!
Can you give us tonight’s TattsLotto numbers as well?
(seeing that you know the contents of a post before it even appears!)
Sheesh, talk about closed minds !
What would those dumb French know about nuclear?
They’re silly enough to produce 80% of their electricity with it and no ACO2!
But I’d ‘a’ thought Ender would like that part.
…. and of course if the Sahara did become green again, that would mean the Mediteranian would probably become anoraebic below two hundred and fifty meters…. like it used to be according to this guy.
http://www.soc.soton.ac.uk/soes/staff/ejr/DarkMed/dark-title.html
Just cut and pasted the address not sure on how to do yer link thingy on this site…. It’s an interesting read.
LoL… Err that would be “Mediterranean”… and anoxic rather than anoraebic.. D’oh!
Completely O/T, but if someone feels too self important, it’s worth watching this! Funny too!!
http://www.jibjab.com/view/122257
I once knew an ethnobotanist, now deceased, who thought that we all gained our powers of speech on the verdant savannas of the late Pleistocene Sahara.
He reckoned that while following the vast herds around hunting and gathering some clever drongo decided to have a taste of the mushrooms that were growing on the herd’s dung in the then moist Saharan climate.
As some of these mushrooms had psychopharmacological effects they were quickly adopted into a nascent shamanic tradition, where synthaesthesiatic symptoms after consumption allowed both the initiated and the uninitiated to hear sights and see sounds, especially once the bright Saharan sun had set, at night around the fire.
And suddenly in the most profound paradigm shift of humanity, a clever drong held up a stone and saw its sound. And in a single moment, he got it! The sound was the stone.
“Stoooooooonnnnneeed.” He formed with his mouth. And that was it. Language was born like that in an instance. The rest is history.
So, (maybe) we owe much more than we think to the verdant savannas of the Sahara and also a lowly fungus that wouldn’t have been growing there if it had always been a desert.
http://ennedi.free.fr/rupestre.htm
http://www.cru.uea.ac.uk/~e118/WS/sahara14/sahara14.htm
If I’ve got this right:-
4300 calender years bp = 2300 BC,
2700 calender years bp = 692 BC
Roman Republic founded 509 BC
Punic Wars 264 – 146 BC
North Africa was a pretty important grain source for Rome.
Has there been any cross checking of the conclusions of this article with Roman (or other) sources from around that era?
Wes George,
You did not, by any chance rediscovered the above mentioned mushrooms?
I don’t know that there is anything “new” in this — here is a report from 2 years ago that says more or less the same thing:
http://www.livescience.com/history/060720_sahara_rains.html (July 2006)
“Or just more ANTHROPOGENIC influence”
Not unless the humans that moved into this area brought their SUVs with them. Mind you, that’s not as silly as it sounds – this article also mentions that:
‘The end of the rains and return of desert conditions throughout the Sahara after 5,500 coincides with population return to the Nile Valley and the beginning of pharaonic society.’
Conventional ‘wisdom’ has it that this pharaonic society was also responsible for the construction of the pyramids. If you can believe that they built pyramids, you can also believe that they built SUVs.
Scumsy – I know anthropogenic is a BIG word for you. But anthropogenic doesn’t has to have a big 8 litre V8 SUV. Could be just humans with seed bags and digging sticks.
Very simply point – humans have the power to consciously change the environment on large scales. I’m not fundamentally in opposition nor in universal agreement. In this case seems to be a smart thing to do. Plant trees. Lots of trees. Sensible adaptation.
Experience, observe, reflect, contemplate, conceptualise, innovate, act, and review.
What it is to be human.
“humans have the power to consciously change the environment on large scales”
And of course you have plenty of peer-reviewed material that substantiates this assertion: that with no more technology than seed bags and digging sticks, humans have been able to CONSCIOUSLY change entire ecosystems and climate patterns.
I’ve been looking for an excuse not to mow the lawn – I think I just found it. Thanks.
Are you kidding – what a ninny ! ROTLMAO
I said consciously change their “environment”. This is their local environment for their purposes.
Side effects are on ecosystems and climate. These may or may not be noticed, considered important, or intentional.
Did I say it had to be primitive peoples. But anyway let’s go with that.
hmmmm – well I guess there’s just agriculture in general, vast regions of cereal production across Eurasia, rice culture of Asia
8000 years of forest clearing
fire stick culture in Australia
then we have cities, megapolis urbania, damming of rivers etc.
changing entire fisheries populations – some to the point of collapse
probably just imagined all that
humans have changed planetary albedo
“40% of Earth’s land has been converted to agriculture. He thus states that today about 40% of the global photosynthesis is now in human hands. He concludes that agriculture has already altered the biosphere as much as projections of future climate change, but now they are happening together…..”
ftp://ftp.iluci.org/LCLUC_APR2007/foley_lcluc_apr2007_presentation.pdf (very good even for sceptics – 20Mb)
does land clearing have a local climate effect – err how about
http://www.iemss.org/iemss2002/proceedings/pdf/volume%20due/154_lyons.pdf note the picture
then I suppose we could get into Ruddiman for some sport
http://courses.eas.ualberta.ca/eas457/Ruddiman2003.pdf
Gee haven’t even got to global warming yet
Don’t have lawns to mow here in my cell. Lucky you.
To Ian Beale.
North Africa – Morocco, Algeria and Tunisia consist of two Halves. North of the Atlas Mountains and South of the Atlas mountains. The North area between the Mountains and the sea has a climate very reminiscent of a country we know well – Australia.
There are huge areas for rice growing.
I worked in a Mountainous area of Algeria. From the roof of my office building I had a 360 degree view to the horizons of Grapes – vineyards. Some of these vineyards dated back to Roman times. Some of the cork trees used to produce the wine bottle corks were planted by the Romans.
Once you pass over the mountains south, the terrain becomes very quickly gibber desert. There are some sand seas on the Algeria – Tunisia – Libya border.
The famous Foreign Legion ( Légion étrangère) headquarters in Algeria was in a place called Sidi Bel Abbès. This was a large farming area.
My mistake in the last post. There are huge areas in Northern Africa for Wheat and Semolina growing not rice. (Doh)