The topic of Lake Chad cropped up on Cliscep the other day, in the context of a comment sent to Robin on his “West vs the rest” hypothesis. This is the relevant excerpt:

Many developing nations — particularly in Africa, South Asia, the Middle East and small island states — are already experiencing severe climate impacts and are among the most vocal advocates for urgent action. Lake Chad is a stark example: once covering around 10,000 square miles and supporting 40–50 million people, [it] has shrunk by around 90%, contributing to humanitarian crises and regional instability. Countries like Chad are highly engaged at COPs precisely because the stakes for them are existential.

The allegation is one we have heard before. (Never mind that the figure of 40-50 million people supported by it is pure bunkum.) A few years ago, when Mark penned Niger Negatives, I looked up some data on Lake Chad levels. There was an old reconstruction showing the main fall in water levels took place in the 1960s, and satellite altimetry data from DAHITI showed no cause for alarm. Of course, that data necessarily ended in 2022, when the comment was made, so perhaps Robin’s correspondent had something more up-to-date. Here is how the most recent DAHITI data, available here, look:

The years are somewhat obscured, but the timeline runs from 1992 to 2025. Of interest may be that the lowest value in the series was in 1993, and the highest in the series was in 2024. I see no cause for alarm here. If the climate “crisis” has evaporated Lake Chad, it must have done it before anyone was even aware of the problem.

The historical reconstruction looks like this. It comes from Earth Observatory here. I have spliced on the (running average to remove annual fluctuations) values for the DAHITI data. As you can see, although they both claim to be measured in metres above sea level, their baselines are offset. Nevertheless, there is still no evidence of a climate “crisis” in the data.

Mentioned on the Earth Observatory page from which the reconstruction comes was a French expedition to the region in the first decade of the twentieth century. Some excerpts follow from Tilho’s presentation to the Royal Geographical Society in 1910, pertaining to the level of Lake Chad his expedition found:

When we arrived at Lake Chad an interesting and difficult geographical problem presented itself before us—

(1) is Lake Chad gradually disappearing, or are its fluctuations subject to a fixed law?

p.271

You understand our curiosity four years after having made our first map of Lake Chad, to see what was the aspect which this constantly changing lake was likely to present. When we arrived in the vicinity of the lake, we learned from the natives that caravans were crossing on dry land the northern portion, which in 1904 we had navigated on board the Benoit Garnier; that the central portion was merely a marsh where no boat could pass; whereas in the southern portion certain channels, which had formerly been closed to navigation, had become once more practicable. The drying-up of the northern portion, we were told, had been so rapid, that a great quantity fish had not had time to flee southwards, and had taken refuge in the depressions, where they had been asphyxiated in the few inches of stagnant and muddy water that had been left behind. For the natives it was quite like a new Miracle of the Fishes; they gathered them in baskets. Even to-day large areas are covered with dead fish. The herds of cattle suffered greatly from this sudden transformation the lake. The stagnant water, saturated with salt, and charged with decomposed matter, became poisonous, and animals perished by hundreds. The rhinoceros, the hippopotamus, the elephant, themselves, disappeared southward in the wake of the retreating water.

p.272

Tilho and crew divided Lake Chad in 1908 into four zones:

1. The dried-up zone

2. The marshy zone

3. The navigable zone

4. The lagoon zone

These are shown on their contemporary map below. For reference, it is followed by a recent Google Earth image, and then an attempt to superimpose the old over the new. It’s not quite in the correct place, because my georeferencing went awry even though latitude and longitude was labelled on the French map. [A congratulatory thimble of Scotch if you can guess why. Answer to follow in a comment.]

Slight offset or not, the map and photograph are substantially similar. In particular, the navigable zone coincides with today’s open water in the southern part.

Now we go forwards in time to an image on the Earth Observatory page, showing a very early satellite photograph of the lake (1963). Here we can clearly see the northern limb is open water.

There is a seeming disconnect between the long-term reconstruction shown on Earth Observatory and the description of Tilho. The reconstruction shows high water, Tilho says the northern limb was dry. The reconstruction certainly matches what we know from 1963 onwards, but it’s dubious whether it captured the long-term variation before then.

The Earth Observatory page also draws the reader’s attention to the Atlantic Multidecadal Oscillation. This has a period of about 70 years, and although it does not match the reconstruction particularly well, there are certainly hints that the changes in Lake Chad might be periodic in nature rather than linear, especially when considering Tilho and colleagues’ observations from 1908. (These match the AMO better than they match the reconstruction.) The image comes from Wiki at this page.

If I may make a Feynmannian attempt to disprove myself here: a critic might say I am using the fact that the bath is full to prove the bathroom has been flooded. There is a shallow sill between the northern and southern limbs of Lake Chad, such that the northern limb will not flood unless the southern reaches a certain depth. So all the oscillations under the sun don’t matter, as the northern part stays dry unless a certain water level is breached. In my defence, I might say if that is true, then the sill was last flooded a long time ago, before any hint that there was such a thing as a climate “crisis.” (Referring to the reconstruction, it was some time during the steep descent of the late 60s.)

A final point to make is that, if Lake Chad is sitting at the level of the aquifer, it will stay wet until the two become detached. Thus, if the locals decide to engage in irrigation to support farming, the result could be a once-and-done disappearance of the remainder of the lake.

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