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October 11, 2003

Verdant Sahara?

This article from US NEWS & World Report discusses an art show displaying the rock paintings of ancient people from the Tassili N'Ajjer of Algeria deep in the Sahara. It depicts a time when the region was more savanna than desert. There are still echoes of this time that have remained to haunt us, I remember a scene from Naturalist David Attenborough's series The Living Planet where he focused in on a lone acacia tree in the Air highlands of northern Niger[1], all that remains of the woodlands of ages gone by. Additionally, there are 10,000 foot mountain ranges in the heart of the Sahara that no doubt served as refugium from the encroaching desert, and still are important nodal points for the networks of the Tuareg people because of the presence of oases around their girdles.

The history of the Sahara should sensitize people to the fact that the earth has been subject to dramatic climatic shifts. We are after all currently likely in an interglacial and wild shifts in climate are not unknown historically.

fn1. The tree's roots had struck a groundwater vein, allowing it to continue surviving in a climatic regime for which it was not adapted.

Posted by razib at 12:28 PM

The rise in CO2 is causing plants to grow back into desert areas. The plants do not need to use as much energy or lose as much moisture to get the amount of CO2 needed and so they are growing into the edges of deserts.

Posted by: Randall Parker at October 11, 2003 10:02 PM

Funny, I had heard that the Sahara was still expanding northward.

Anyway, you don't need to go back as far as cave paintings to find evidence of a wetter climate in North Africa. In Roman times the Qattara depression was a lake, and in ancient Egypt the areas outside the Nile valley still had lions and plentiful game (though already too dry for farming). The Sphinx has quite a bit of water erosion (which fringe characters like Graham Hancock take as evidence of vast antiquity, but which likely just shows that there was a lot more rain there a few thousand years ago).

If the thermohaline conveyor that keeps Europe temperate stops, perhaps we will suddenly see rainfall in North Africa increase again. Wonder whether anyone has done climate modeling that shows this?

Posted by: bbartlog at October 13, 2003 09:15 AM

boris-well, the sahara is pretty dependent on how far the trades go north and the westerlies go south. if the earth warms, the subtropical belt should shift north-ergo, the med. climate push into europe and the desert into the med. while the sahel moves north as the trades push up further. if the climate cools, the north sahara gets a med. climate as the westerlies come down south much further.

Posted by: razib at October 13, 2003 11:53 AM