The Sahara used to be a verdant relative paradise
How did it change?
The Sahara is perhaps the world’s most iconic desert. Big dunes, camels, lots and lots of sand, and not a drop of water in sight. But somewhere around 10,000 years ago, it was much different! In fact, some theories suggest that the Sahara could have been a jungle similar to the Amazon. So what happened? Well there are a couple different ideas about that.
A green Sahara?
When I say the Sahara used to be green, or verdant, or even a jungle, that probably conjures up specific images in your head. And, in truth, we don’t know exactly what the Sahara looked like during this period of time. However, in 2002, scientists made a pretty amazing discovery: crocodiles were living in the Sahara near the southern edge of the desert. This might not seem like a big deal, but crocodiles need water to live and the fact that they were living in the desert, where they had been able to adapt, gives us a little bit of an idea of what the Sahara might have looked like:
Which is something like this. At least in certain places. There is, of course, a lot of speculation around what the Sahara could have been. Some theories suggest some areas might have even been a thicker sort of jungle. What we do know though is that, even as “early” back as the Roman Empire, that the Sahara was a much wetter place than it is today.
Regardless, today the Sahara is the world’s largest, continuous desert outside of Antarctica. So how did it end up that way if it was once so relatively green?
A tilt of the Earth’s axis
One theory, dating back a few decades, suggest that the reason for the Sahara’s dramatic desertification is because of the planet at large. A relatively subtle shift in the planet’s axis might have been all that was needed to careen the Sahara into the sandy desert we know today.
Some 9,000 years ago, Earth's tilt was 24.14 degrees, as compared with the current 23.45 degrees today.
This had a gradual impact on the summer monsoon season that Africa experiences. During the time before the shift, climate models suggest that the monsoon would hit the Sahara and thus bring about grasses, plants, and a general and relative abundance of water.
But while the tilt shift was probably the catalyst, the desertification of the Sahara was still very fast, much too fast for it to have been solely responsible for what the Sahara looks like today. For that, a new theory has been formulated!
Humans vs. the Earth
If you thought that, for once, humans might escape some blame for a radical shift in the planet’s natural environment, you are going to be disappointed! As it turns out, humans were likely very much involved in helping this process along. Humans, and their domesticated grazing animals such as goats and cattle, are probably the reason for why the Sahara looks like it does today, a process that otherwise could have taken thousands more years to occur.
Because while the tilt shift of the Earth brought about it a change to the overall precipitation to the area, the shift was gradual and not very dramatic. Nobody woke up one morning to an axis that was 0.69 degrees off. So while the area was gradually getting dryer through the centuries, it would have taken much longer for this kind of dramatic transformation to happen. But when an area is already experiencing desertification, and you also have large mammals eating plants and grasses, you experience a compounding effect.
By overgrazing the grasses, they were reducing the amount of atmospheric moisture—plants give off moisture, which produces clouds—and enhancing albedo.
And so while humans might not be to blame for the Sahara drying out entirely, we certainly did speed along the process. Not that any humans back then could have known any of the impacts or effects of what they were doing. But it does show that humans have been having a profound impact on the natural environment for a long, long time.
Thanks for shedding light on this -- I knew about the "green" Sahara but didn't know the hypotheses for the shift. I've been quite enjoying your Substack lately because of posts like this.