Sahara desert

[Guest bgjyd834]

Do the boundary of the Sahara desert goes through cycles ?

 

Could there be as the Atlantic ocean gets warmer the desert will bloom ?

[rktpro]

 

Could there be as the Atlantic ocean gets warmer the desert will bloom ?

 

My geography teacher says that Sahara was once a large sea. I don't believe, actually.

[SMF]

This is just south of the Sahara, but it seems very relevant- http://portal.iri.columbia.edu/~alesall/pubslist/gloplacha2008final.pdf

SM

[JohnB]

My geography teacher says that Sahara was once a large sea. I don't believe, actually.

 

Considering the number of whale fossils in the Sahara, maybe you should.

[Doc. Josh]

NA JohnB the whale fossils flew into the desert. You know that

[JohnB]

I thought the fins looked rather big.

[insane_alien]

I thought the fins looked rather big.

 

it was the many empty remains of canisters of helium that got me.

[Moontanman]

Everyone is in rare form this day,

 

http://en.wikipedia.org/wiki/Sahara

 

People lived on the edge of the desert thousands of years ago[4] since the last ice age. The Sahara was then a much wetter place than it is today. Over 30,000 petroglyphs of river animals such as crocodiles [5] survive, with half found in the Tassili n'Ajjer in southeast Algeria.

 

The climate of the Sahara has undergone enormous variation between wet and dry over the last few hundred thousand years.[11] During the last glacial period, the Sahara was even bigger than it is today, extending south beyond its current boundaries.[12] The end of the glacial period brought more rain to the Sahara, from about 8000 BC to 6000 BC, perhaps because of low pressure areas over the collapsing ice sheets to the north.[13]

 

Once the ice sheets were gone, northern Sahara dried out. In the southern Sahara though, the drying trend was soon counteracted by the monsoon, which brought rain further north than it does today. The monsoon season is caused by heating of air over the land during summer. The hot air rises and pulls in cool, wet air from the ocean, which causes rain. Thus, though it seems counterintuitive, the Sahara was wetter when it received more insolation in the summer. This was caused by a stronger tilt in Earth's axis of orbit than today, and perihelion occurred at the end of July around 7000 BC.[14]

 

By around 3400 BC, the monsoon retreated south to approximately where it is today,[15] leading to the gradual desertification of the Sahara.[16] The Sahara is now as dry as it was about 13,000 years ago.[11] These conditions are responsible for what has been called the Sahara pump theory.

 

The Sahara has one of the harshest climates in the world. The prevailing north-easterly wind often causes sand storms and dust devils.[17] When this wind reaches the Mediterranean, it is known as sirocco and often reaches hurricane speeds in North Africa and southern Europe. Half of the Sahara receives less than 20 mm (0.79 in) of rain per year, and the rest receives up to 100 mm (3.9 in) per year.[18] The rainfall happens very rarely, but when it does it is usually torrential when it occurs after long dry periods.

 

The southern boundary of the Sahara, as measured by rainfall, was observed to both advance and retreat between 1980 and 1990. As a result of drought in the Sahel, the southern boundary moved south 130 kilometres (81 mi) overall during that period.[19]

 

Recent signals indicate that the Sahara and surrounding regions are greening because of increased rainfall. Satellite imaging shows extensive regreening of the Sahel between 1982 and 2002, and in both Eastern and Western Sahara a more than 20 year long trend of increased grazing areas and flourishing trees and shrubs has been observed by climate scientist Stefan Kröpelin.[20]

Edited May 7, 2011 by Moontanman