y:why it matters
Click Here
ad info The story of our times.  CNN.com/ColdWar
The story of our times. CNN.com/ColdWar





   SPECIAL DEAL:
Live plants from only $30
CLICK HERE
 

The Flower Club
CNNin
 MAIN PAGE
 WORLD
 U.S.
 LOCAL
 POLITICS
 WEATHER
 BUSINESS
 SPORTS
 SCI-TECH
 NATURE
 ENTERTAINMENT
 BOOKS
 TRAVEL
 FOOD
 HEALTH
 STYLE
 IN-DEPTH

 custom news
 Headline News brief
 daily almanac
 CNN networks
 CNN programs
 on-air transcripts
 news quiz

  CNN WEB SITES:
CNN Websites
 TIME INC. SITES:
 MORE SERVICES:
 video on demand
 video archive
 audio on demand
 news email services
 free email accounts
 desktop headlines
 pointcast
 pagenet

 DISCUSSION:
 message boards
 chat
 feedback

 SITE GUIDES:
 help
 contents
 search

 FASTER ACCESS:
 europe
 japan

 WEB SERVICES:

 


 
NATURE

Sahara turned to desert in abrupt climate change

desert

July 15, 1999
Web posted at: 4:27 p.m. EDT (2027 GMT)

WASHINGTON (AP) -- The rains stopped coming, the temperature rose and the great grasslands of North Africa turned to desert a few thousand years ago -- changes that may have helped spur development of civilization in the Nile Valley.

The change to today's arid climate was not gradual, but occurred in two episodes -- the first 6,700 to 5,500 years ago and the second 4,000 to 3,600 years ago, according to a paper published Thursday by the journal Geophysical Research Letters.

"The latter was very severe, ruining ancient civilizations and socio-economic systems," the researchers wrote.

A team of researchers headed by Martin Claussen of Germany's Potsdam Institute for Climate Impact Research analyzed computer models of climate over the past several thousand years.

They concluded that the change to today's desert climate in the Sahara was triggered by changes in the Earth's orbit and the tilt of Earth's axis.

While the changes in Earth's orbit occurred gradually, the switch in North Africa's climate and vegetation was abrupt. In the Sahara, "we find an abrupt decrease in vegetation from a green Sahara to a desert shrubland within a few hundred years," the scientists reported.

No longer were grasses and other plants collecting water and releasing it back into the atmosphere; now sand baked in the stronger sun and rivers and streams dried up.

This event devastated ancient civilizations in the moist desert, now remembered only by rock paintings. The change may have spurred them to move to the Nile Valley and other river valleys where great civilizations developed.

"The migration of people from the Sahara to the Nile is a hypothesis," Claussen said.

"Whether or not this migration was the stimulus for the high civilization there is not yet known. ... For me it seems plausible," he said.

Claussen and his team used computer models of climate to calculate the impact of weather, oceans and vegetation separately and in various combinations. They concluded that oceans played only a minor role in the Sahara's desertification.

The research also suggested that land use practices of humans who lived in and cultivated the Sahara were not significant causes of the desertification.

Claussen noted that changes in the Earth's orbit and tilt will continue to occur in the future.

As to their effects, he said: "What will happen in the future, frankly, we can only speculate."

Copyright 1999   The Associated Press. All rights reserved.



RELATED STORIES:
New York prepares for climate change
June 8, 1999
Nuclear sub dives under the ice to explore climate change
April 19, 1999
Study links solar activity to Earth's climate
April 13, 1999
Warm Arctic may enhance global warming
March 1, 1999


RELATED SITES:
Potsdam Institute for Climate Impact Research
National Center for Atmospheric Research
Note: Pages will open in a new browser window

External sites are not endorsed by CNN Interactive.

 LATEST HEADLINES:

WORLD:
India claims retreat of guerrillas from Kashmir almost complete
China tirade on Taiwan carries olive branch
Despite setback, sides in Belfast crisis working to move forward

US:

Senate approves GOP's version of 'patients' bill of rights'
Lawyer says 'Railway Killer' suspect unaware he faced death penalty
Barak says he's ready for 'painful compromise' for peace

SCI TECH:

Back Orifice 2000 under control

ENTERTAINMENT:

Review: 'Eyes Wide Shut' - All undressed with no place to go

SPORTS:


Pampling unlikely leader at Carnoustie
Mantei blows win for D'backs' Johnson

BUSINESS:

Bourses off in early trade
China-Taiwan strains hit Hong Kong
Nasdaq, S&P hit highs

Launch CNN's Desktop Ticker and get the latest news, delivered right on your desktop!

Today on CNN
SEARCH CNN.com
Enter keyword(s)   go    help

Back to the top   © 1999 Cable News Network. All Rights Reserved.
Terms under which this service is provided to you.
Read our privacy guidelines.