Thanks, that is quite interesting, and I had missed seeing it. I would have guessed that the Sahara was last greened at the beginning of the last glacial.
-Pete On Fri, 24 May 2013, D & N wrote: > Saw this yesterday, with time line encapsulations below: > N. > http://www.livescience.com/4180-sahara-desert-lush-populated.html > > > Sahara Desert Was Once Lush and Populated > > Bjorn Carey > Date: 20 July 2006 Time: 10:07 AM ET > > At the end of the last Ice Age, the Sahara Desert was just as dry and > uninviting as it is today. But sandwiched between two periods of extreme > dryness were a few millennia of plentiful rainfall and lush vegetation. > > During these few thousand years, prehistoric humans left the congested Nile > Valley and established settlements around rain pools, green valleys, and > rivers. > > The ancient climate shift and its effects are detailed in the July 21 issue of > the journal /Science/. > > *When the rains came* > > Some 12,000 years ago, the only place to live along the eastern Sahara Desert > was the Nile Valley. Being so crowded, prime real estate in the Nile Valley > was difficult to come by. Disputes over land were often settled with the fist, > as evidenced by the cemetery of Jebel Sahaba where many of the buried > individuals had died a violent death. > > But around 10,500 years ago, a sudden burst of monsoon rains over the vast > desert transformed the region into habitable land. > > This opened the door for humans to move into the area, as evidenced by the > researcher's 500 new radiocarbon dates of human and animal remains from more > than 150 excavation sites. > > "The climate change at [10,500 years ago] which turned most of the [3.8 > million square mile] large Sahara into a savannah-type environment happened > within a few hundred years only, certainly within less than 500 years," said > study team member Stefan Kroepelin of the University of Cologne in Germany. > > *Frolicking in pools* > > In the Egyptian Sahara, semi-arid conditions allowed for grasses and shrubs to > grow, with some trees sprouting in valleys and near groundwater sources. The > vegetation and small, episodic rain pools enticed animals well adapted to dry > conditions, such as giraffes > <http://www.livescience.com/853-giraffes-dizzy.html>, to enter the area as > well. > > Humans also frolicked in the rain pools, as depicted in rock art from > Southwest Egypt. > > In the more southern Sudanese Sahara, lush vegetation, hearty trees, and > permanent freshwater lakes persisted over millennia. There were even large > rivers, such as the Wadi Howar, once the largest tributary to the Nile from > the Sahara. > > "Wildlife included very demanding species such as elephants, rhinos, hippos, > crocodiles, and more than 30 species of fish up to 2 meters (6 feet) big," > Kroepelin told /LiveScience/. > > A timeline of Sahara occupation [See Map]: > > * 22,000 to 10,500 years ago: The Sahara was devoid of any human > occupation outside the Nile Valley and extended 250 miles further > south than it does today. > > * 10,500 to 9,000 years ago: Monsoon rains begin sweeping into the > Sahara, transforming the region into a habitable area swiftly > settled by Nile Valley dwellers. > > * 9,000 to 7,300 years ago: Continued rains, vegetation growth, and > animal migrations lead to well established human settlements, > including the introduction of domesticated livestock such as sheep > and goats. > > * 7,300 to 5,500 years ago: Retreating monsoonal rains initiate > desiccation in the Egyptian Sahara, prompting humans to move to > remaining habitable niches in Sudanese Sahara. 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. > > Related Stories > > * Deserts Might Grow as Tropics Expand > <http://www.livescience.com/10472-deserts-grow-tropics-expand.html> > * Drought Conditions Worsen in Parts of U.S. > <http://www.livescience.com/4124-drought-conditions-worsen-parts.html> > * Singing Sand Dunes: The Mystery of Desert Music > > <http://www.livescience.com/3788-singing-sand-dunes-mystery-desert-music.html> > * Ancient People Followed 'Kelp Highway' to America > > <http://www.livescience.com/7042-ancient-people-kelp-highway-america-researcher.html> > * Scientists To Study Monsoon Formation > > > > > On 24/05/2013 7:37 AM, Ray Harrell wrote: > > I've often wondered how the huge populations of Southern Mexico and Brazil > > prior to 1492 and their water use, didn't create a desert as in the Sahara > > and the Middle East. Once the people were gone, the forests came back and > > took over. The rains returned and the aquifers filled up again as in > > Mexico. that didn't happen in Northern Africa and the Middle East. > > > > REH > > > > -----Original Message----- > > From: futurework-boun...@lists.uwaterloo.ca > > [mailto:futurework-boun...@lists.uwaterloo.ca] On Behalf Of pete > > Sent: Friday, May 24, 2013 5:26 AM > > To: RE-DESIGNING WORK, INCOME DISTRIBUTION, EDUCATION > > Subject: Re: [Futurework] US underground water levels dropping fast > > > > > > > > On Thu, 23 May 2013, de Bivort Lawrence wrote: > > > > > Sorry, I meant to add: there is a LOT of aquifer water under major > > > tracts of desert Sahara, so I don't think aquifer depletion led to the > > > desertification of the Sahara. Ditto with the Rub al-Khali, Saudi > > > Arabia huge desert, but I don't know about the possible role of wood > > > chopping and goat grazing there. > > > > > > Cheers, Lawry > > I would have thought that these would be more culpable in Arabia, as the > > south edge of the peninsula has been continuously relatively verdant, and > > presumably populated, since people first came out of Africa, and it is a > > relatively small region compared to the Sahara, so the impact of people > > moving inland could easily affect the whole empty quarter. With the Sahara, > > it seems an awfully large area to be influenced by the presumably small > > population of prehistory, although, as with much of the Mediterranean, I can > > see how people and goats could expand the desert boundaries, as the > > presumably much larger current population seems to be doing in the Sahel. I > > believe the Atlas Mountains were said to be thickly forested three millennia > > ago. But I rather suspect the band 250km north and south from 23deg north > > latitude would be a pretty fearsome desert even if no humans nor goats had > > ever trod there. > > > > Oh, in fact I now recall that satellite imagery has revealed well trodden > > trade routes which have pinpointed the location of the remains of ancient > > villages running north from Oman, and now covered in places by 100ft sand > > dunes, so clearly that area was populated at a time when it was much more > > habitable. Which doesn't demonstrate any causality, but indicates the > > possibility. > > > > -Pete > > > > > > > > On May 23, 2013, at 7:36 AM, Ray Harrell wrote: > > > > > > > Is this the way the Sahara Desert happened? > > > > REH > > > > From: futurework-boun...@lists.uwaterloo.ca > > > > [mailto:futurework-boun...@lists.uwaterloo.ca] On Behalf Of D & N > > > > Sent: Wednesday, May 22, 2013 3:55 PM > > > > To: RE-DESIGNING WORK, INCOME DISTRIBUTION, EDUCATION > > > > Subject: [Futurework] US underground water levels dropping fast > > > > > > > > http://www.reuters.com/article/2013/05/20/us-usa-water-idUSBRE94J0Y9 > > > > 20130520 > > > > > > > > Drop in U.S. underground water levels has accelerated: USGS > > > > > > > > By Environment Correspondent Deborah Zabarenko > > > > > > > > WASHINGTON | Mon May 20, 2013 7:10pm EDT > > > > > > > > (Reuters) - Water levels in U.S. aquifers, the vast underground > > > > storage areas tapped for agriculture, energy and human consumption, > > > > between 2000 and 2008 dropped at a rate that was almost three times > > > > as great as any time during the 20th century, U.S. officials said on > > > > Monday. > > > > > > > > The accelerated decline in the subterranean reservoirs is due to a > > > > combination of factors, most of them linked to rising population in > > > > the United States, according to Leonard Konikow, a research > > > > hydrologist at the U.S. Geological Survey. > > > > > > > > The big rise in water use started in 1950, at the time of an > > > > economic boom and the spread of U.S. suburbs. However, the steep > > > > increase in water use and the drop in groundwater levels that > > > > followed World War 2 were eclipsed by the changes during the first > > > > years of the 21st century, the study showed. > > > > > > > > As consumers, farms and industry used more water starting in 2000, > > > > aquifers were also affected by climate changes, with less rain and > > > > snow filtering underground to replenish what was being pumped out, > > > > Konikow said in a telephone interview from Reston, Virginia. > > > > > > > > Depletion of groundwater can cause land to subside, cut yields from > > > > existing wells, and diminish the flow of water from springs and > > > > streams. > > > > > > > > Agricultural irrigation is the biggest user of water from aquifers > > > > in the United States, though the energy industry, including oil and > > > > coal extraction, is also a big user. > > > > > > > > The USGS study looked at 40 different aquifers from 1900 through > > > > 2008 and found that the historical average of groundwater depletion > > > > - the amount the underground reservoirs lost each year - was 7.5 > > > > million acre-feet (9.2 cubic kilometers). > > > > > > > > From 2000 to 2008, the average was 20.2 million acre-feet (25 cubic > > > > kilometers) a year. (An acre-foot is the volume of water needed to > > > > cover an acre to the depth of one foot.) > > > > > > > > One of the best-known aquifers, the High Plains Aquifer, also known > > > > as the Oglala, had the highest levels of groundwater depletion > > > > starting in the 1960s. It lies beneath parts of South Dakota, > > > > Nebraska, Wyoming, Colorado, Kansas, Oklahoma, Texas and New Mexico, > > > > where water demand from agriculture is high and where recent drought > > > > has hit hard. > > > > > > > > Because it costs more to pump water from lower levels in an aquifer, > > > > some farmers may give up, or irrigate fewer fields, Konikow said. > > > > Another problem with low water levels underground is that water > > > > quality can deteriorate, ultimately becoming too salty to use for > > > > irrigation. > > > > > > > > "That's a real limit on water," Konikow said. "You could always say > > > > that if we have enough money, you build a desalization plant and > > > > solve the problem, but that really is expensive." > > > > > > > > (Reporting by Deborah Zabarenko; Editing by Leslie Adler) > > > > > > > > _______________________________________________ > > > > Futurework mailing list > > > > Futurework@lists.uwaterloo.ca > > > > https://lists.uwaterloo.ca/mailman/listinfo/futurework > > > > > _______________________________________________ > > Futurework mailing list > > Futurework@lists.uwaterloo.ca > > https://lists.uwaterloo.ca/mailman/listinfo/futurework > > > > _______________________________________________ > > Futurework mailing list > > Futurework@lists.uwaterloo.ca > > https://lists.uwaterloo.ca/mailman/listinfo/futurework > > > > _______________________________________________ Futurework mailing list Futurework@lists.uwaterloo.ca https://lists.uwaterloo.ca/mailman/listinfo/futurework
