Well @mountainwashere, you have done an admirable job of one-upping me on this subject. :c) Well done, both for your writing and your research - and thank you kindly also for the mentions. ^_^
There are a few aspect where I'm sure you're fine with me pushing back on however (and I'll keep my points brief so as not to be tempted to turn it into a post (two-thumbs up by the way). ^_^
First things first however. You are stimulating discussion, and not merely being "a Debbie Downer". You're cool. ;c)
I am aware that desert, and especially Savannah, is able to sustain the livelihoods of a fair few species. That being said, considering that the Sahara desert alone is comparable in size to the entirety of the United States of America, I would posit the notion that diminishing the boundaries of the Sahara would leave plenty enough area for those species to thrive in regardless.
Human understanding of managed forestation projects has improved since the incidents that you mentioned. I was personally thinking that a casual approach of 'pass the water and the vegetation will come' would be one way of allowing nature to decide on how to best make use of the new inroads of water supply. That being said, it may well be desired for food crops also to feed off of such sources.
I quite agree that a significant impact upon weather in the vicinity may be noted. That moisture will feed weather systems. That being said, I don't think we'll be seeing typhoons any time soon - since these require far bigger bodies of water to build the required strength. More likely are drizzles or rains hundred of miles away fed by the evaporation.
I personally disagree that shifting the land status from desert to Savannah or greener would trigger other places to become deserts. We are not talking of rerouting rivers to figuratively rob Paul to pay Saul (as per the Aral Sea). We are talking of tapping into a big source of water (initially the Mediterranean Sea) to artificially hydrate that which would otherwise be further prone to desertification. I also suspect that the dust needs of the Amazon forest would either be met well enough by half the Sahara desert's present size - and if not - that an alternative could be found either by humanity or the forest's own adaptation.
In spite of sall these differences in perspective, I would certainly agree that geoengineering is a 'potentially' hazardous practice. The degree to which this is so may be measure both in terms of the aims of a given project as well as in terms of the level of understanding of the leadership concerned.
I think that I've covered the main points that I wished to cover. :c) Again, thank you for stimulating discussion - whether it be on my post or a post of your own. Your cautioning is warranted - but I also feel that the possibilities equally warrant exploration.
They definitely do warrant exploring- there have been some successful cases of geoengineering in the past, most notably the Dutch lowlands and the Native American methods of forestry management. There's a commonality between these and the other successful instances of it- it's done very, very cautiously, with ample knowledge of the function of the environment around them,an awareness that it takes constant effort to maintain, and a willingness to nudge nature in a new direction rather than trying to wrestle it whenever possible. It's also generally safer to perform said nudges in more robust ecosystems like temperate old growth forests, rather than more delicate ones like deserts. Overall, though, the failure rate for geoengineering projects is extremely high in the long term- unfortunately, however, we aren't very good as a species at thinking in the lomg term, and short term success is extremely attractive.
Very good points made throughout @mountainwashere. :c)
The truth is that the success or otherwise of a project tends to be measured through human-centric metrics. Would certain aforementioned forestation projects have been deemed a failure had there not been a drop-off in land productivity over a few years? The answer would likely have been in the negative.
A departure from such human-centricity permits a more holistic approach better-compatible with the ways of the Native Americans and others who remained spiritually close to the lands upon which they lived.
In the relative absence of such an affinity one would indeed need to engage the environment with caution and knowledge (the latter only coming about through drawing upon that which has been tried and through progressive experimentation).
And through beginning with a single project in, say, Algeria one would be indulging in that spirit of experimentation and learning that would constitute less of a shove and more of a nudge in the context of the entire Sahara (and there would be plenty of Sahara remaining for species encountering hardship from those nudges to retreat into).
You are very correct in noting that humans are better at thinking short term than long term. We want gratification. We want it now. It drives our decision making process - often enough to ruinous ends.
However one should also recognize that the story of humanity's journey toward achieving flight was strewn with failures and learning before the first rays of success led to a continuing era where commercial flight has grown to be the norm.