Book Review: When the Sahara Was Green

Williams, Martin. When the Sahara was Green: How Our Greatest Desert Came to Be. (Princeton U.P. 2021) Kindle Edition.

Once upon a time, millions of years, tens of thousands of years ago, the region called teh Sahara was green. Sometimes it held enormous rivers. Volcanoes erupted, were crowned with glaciers, and fell silent. Huge fish swam in the giant lakes and rivers. Lush vegetation of varying kinds grew on the land.

Then something happened. Actually, a very large number of somethings, including the entire continent moving in such a way that tucked the Sahara into a dry swath of climate, and Europe (the landmass) cutting the moisture supply to the northern regions. All long before humans ever wandered the landscape. So, as Dr. Williams points out, you can’t blame humans for the desert. Which may be the most useful point in the book.

Martin Williams is a geologist who specializes in deserts and how they got that way. His first introduction to the Sahara came in 1970, when the group he was with couldn’t go to Libya because of a coup in progress, so they went to an even drier region instead. As he and the group leader went ahead of the others (on camel, as the others got the Land Rovers and other vehicles repaired), Williams noticed evidence of human presence, and of a river, in a place where no water could be seen. That made him curious, and the rest is this book.

Half geology and half travel, the book is a very readable account of the Sahara’s deep history, going back to the Cambrian. It has nice maps and diagrams, although more would be useful, especially in the e-book version. The illustrations are hot-linked, as are the end-notes, so you can go back and forth, but that gets tiresome so I just studied the major diagrams and memorized what was where. Williams has a knack for translating from geology into good prose, and blends the deep past with more recent explorations and observations. He works roughly chronologically after the introduction, going back to the Cambrian and moving toward the present climate regime.

Contrary to popular understanding (and most nature shows I’ve seen), the Sahara is not an endless sea of tan dunes. About a quarter at most of the land is sandy. This is in part because sand is needed to make sand, and large swaths of the area don’t have the right rocks. More common are huge rocky “pavements”, and clumps of hard, black or red hills. Some are volcanic, some are tougher sedimentary remnants (think Ayers Rock/Uluru in Australia). Volcanoes in East Africa played a role in drying the region, blocking flow from what is now the Indian Ocean. Africa moving north to collide with Europe, closing the Tethys Sea, didn’t help, since what is now the Med has gone completely dry, most recently during the last phase of the Ice Age. Then things improved until the Younger Dryas, before returning to the current arid phase.

The edges of the desert move. This is not, as Williams points out, because of overgrazing, slash-and-burn farming, or air chemistry. It is because of changing rainfall patterns linked to the North Atlantic Oscillation and the El Niño/Southern Oscillation and Indian Ocean monsoon. How are they connected? No one knows yet, but there are a lot of guesses. In wetter phases, the North African grasslands and brush move south, or the sahel region moves north. When things dry out, the Sahara grows once more.

Humans didn’t cause this, but modern governments can make things worse for the people of the desert. Ordering Bedouin and others to stop moving, even when drought moves in for a decade or two, causes misery for the nomads and for the farmers around them. Killing off livestock “to stop overgrazing” isn’t the best answer, per Williams. Understanding the actual reason for the drought, and making space for people to respond in ways that work, is the better solution.

Williams is concerned about human effects on the environment, but he’s not pounding the “two legs bad, four legs good” drum that so many do. I suspect his background being in geology makes the difference – he’s used to looking at the looooooooong term. He talks about the humans who lived in what is now the desert, how they coped with the gradual changes and shifts, and what we know and don’t know.

I highly recommend this book. You don’t have an earth-science background to enjoy it, but it does make for faster reading. The illustrations and charts are good, and there are lots and lots of endnotes for those who want more.

FTC Notice: I purchased this book for my own use and received no remuneration or consideration from the author or publisher for this review.

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9 thoughts on “Book Review: When the Sahara Was Green

  1. I’ve read pieces about this, but never an entire book. The oscillations and changed rainfall may also have lead to the end of Africa as Rome’s granary, and reliance on what Egypt could provide.

    • *wags paw* Egypt during Roman times, yes. The Nile has always fluctuated with El Niño, but how and why are still not entirely clear. Northern Africa . . . Williams has some doubts, and I have an older book (early 2000s) that argues that North Africa outside of Egypt wasn’t the bread basket Roman writers claimed, even in good years. I need to go back and re-read that one, since it’s been a while.

  2. Obviously human time-travelers created the Sahara Desert. [Very Big Crazy Grin]

  3. Interesting, I’ll have to see if I can find a copy. Yes, there are more than a few ‘rivers’ that were found years ago by another ‘program’, but they were long dry…

  4. Over the past few years I’ve been digging into early human prehistory, and Africa is definitely part of it. I’m interested in the timing of the wet/dry cycles, especially in the Eastern Sahara and upper Nile region during the Pleistocene epoch because that has a bearing on the stories I want to write. Thanks for the review and recommendation.

    • I first ran across the Nile/ENSO link in an academic paper in, I think, *Quaternary Studies* or a climatology journal. This book has excellent endnotes, and I bet you could find more recent studies there.

  5. Went and ordered the hardcover since I find it easier to go back and forth between maps and verbiage in an actual paper book. I am darn close to needing to build another bookcase darn it. 😉

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