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Comment by XaspR8d | Hacker News Reader

Tangent - is there a systems reason (aside from the "base ecological ethics" of wanting to preserve biodiversity and not eradicate any unique ecosystems) why humans would not want to get rid of deserts?

Obviously having more arable or at least livable land is useful to human society, but I generally assume that messing with any large scale climates or biomes has adverse effects. I'm not yet aware of what that would be for deserts though. I suppose they have fairly high albedo, unlike most land formations that can exist in lower latitudes.

(To be clear my own views aren't necessarily so utilitarian and I like deserts. Just curious about a rational geoengineering civilization might do.)

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Some deserts are quite natural. It doesn't matter what you do to them short of knocking down the mountains upwind of them, they're going to be deserts.

Some are not.

I consult my mental image of deserts and I observe that the Sahara is almost devoid of life, whereas the deserts of the American Southwest are rich and diverse despite their lack of substantial rainfall. (The latter I've also visited and spent some time in. I've never been to the Sahara to know if that's correct.) If my mental image is accurate, fixing the unnatural, almost entirely uninhabited desert would be nothing but a win. "Fixing" the natural kind would be relatively destructive of an existing ecosystem.

(Then you get into the question of "how do you valuate and compare two different ecosystems?". I've thrown that gauntlet a couple of times and I don't think I've even seen anyone engage with that question properly in a non-knee-jerk way. The heuristics people have been taught to use about environmentalism do not admit of that question even existing.)

Also note that some deserts are variable, and human activity can tip the balance [1].

especially considering the global carbon balance, it seems that tipping some parts of the desert back to forest would be a net plus. Humans are already doing massive uncontrolled experiments with bad results, it may help some to do some deliberate experiments with good foundations with the goal of creating good results?

[1] https://www.smithsonianmag.com/science-nature/what-really-tu...

>Tangent - is there a systems reason (aside from the "base ecological ethics" of wanting to preserve biodiversity and not eradicate any unique ecosystems) why humans would not want to get rid of deserts?

Getting rid of deserts could actually be quite bad for other ecosystems. The Amazon is fertilized by the Sahara for example https://www.nasa.gov/content/goddard/nasa-satellite-reveals-...

That's incredible. I assumed arrogantly it was mostly inert silica, not phosphorous.

Yeah the earth is a very complex system. When YC came out and proposed the idea of proposed turning the Sahara into a bunch of algae ponds [1] I cringed. First the plan requires more power than we currently produce just to pump all the water but then you would drastically reduce how much gets blown over to the Amazon AND you would suddenly introduce a tremendous amount of moisture to the atmosphere which would almost certainly change global weather patterns.

All of that moisture could cause a considerable increase in rainfall for somewhere (presumably the Amazon, I don't know anything about weather modelling though and am just guessing) which could be catastrophic for life there and even result in tremendous economic losses.

Even relatively small scale geoengineering like damns can have profound negative impacts on ecosystems with some being very predictable and some being completely wildcard. We know the Sahara fertilizes the Amazon but what level does it effect marine life by feeding stuff at the bottom of the food chain (plankton for example) and what would removing that mineral/nutrient source do to the food chain, would it increase rains (and cloud cover) over that area of ocean that might change temperatures subtly enough to make an impact on currents, etc. We're at the point now as a species where we have the power of gods but can't begin to understand the implications of what we are capable of doing.

[1] http://carbon.ycombinator.com/desert-flooding/

We know the Sahara was green, not too long ago. What do we know about the Amazonas from that time? Was it barren because it lacked the input? Was it agricultural land, worked by long overgrown cities by some sunken civilization? I've read about that somewhere, where LIDAR found signs of that, similar to what the Aztecs had.

I've read multiple times that the dust from the sahara makes it over the atlantic and works as fertilizer for the amazonian rain forests. That is relatively new knowledge, since about a decade or so. Has been featured in nature documentations also. What is not known is how much dependence there is on this input. Whereas i'm asking myself what about the other sand deserts then, like the Namib, or Gobi?

If we wait long enough, the planet is going to get rid of the desert.

> For several hundred thousand years, the Sahara has alternated between desert and savanna grassland in a 20,000 year cycle[8] caused by the precession of the Earth's axis as it rotates around the Sun, which changes the location of the North African Monsoon. The area is next expected to become green in about 15,000 years (17,000 AD).

Humans have been creating deserts for thousands of years, by denuding forests. Grow trees there again, and the forests will bring their own water, after a time.

Petra used to be forest. So did much of the North American southwest.

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