As usual, gwern has made a great comment. But I'm going to bite the bullet and come out in favor of the tree plan. Let's go back to the 1830s.
My fellow Swedes! I have a plan to plant 34,000 oak trees. In 120 years we will be able to use them to build mighty warships. My analysis here shows that the cost is modest while the benefits will be quite substantial. But, I hear you say, what if some other material is used to build warships in 120 years? Well, we will always have the option of using the wood to build warships and if we won't take that option it will be because some even better option will have presented itself. That seems like a happy outcome to me. And wood has been useful for thousands of years - it will surely not be completely obsolete in a century. We could always build other things from it, or use it for firewood or designate the forest as a recreational area for esteemed noblemen such as ourselves. Or maybe the future will have some use for forests we cannot yet anticipate [carbon sequestration]. I don't see how we can really go wrong with trees.
Back to the present. I'm concerned with avoiding disasters. "The benefits of this long-term plan were not realized because something even better happened" is only a disaster if the cost of the plan was disastrous. Of course, some people argue that the costs of addressing some of Dr. Jubjub's problems are disastrous and that's something we can discuss on the merits.
My analysis here shows that the cost is modest while the benefits will be quite substantial.
Do show your analysis :-) Don't forget about discounting and opportunity costs :-D
Dr. Jubjub: Sir, I have been running some calculations and I’m worried about the way our slithy toves are heading.
Prof. Bandersnatch: Huh? Why? The toves seem fine to me. Just look at them, gyring and gimbling in the wabe over there.
Dr. Jubjub: Yes, but there is a distinct negative trend in my data. The toves are gradually losing their slithiness.
Prof. Bandersnatch: Hmm, okay. That does sound serious. How long until it becomes a problem?
Dr. Jubjub: Well, I’d argue that it’s already having negative effects but I’d say we will reach a real crisis in around 120 years.
Prof. Bandersnatch: Phew, okay, you had me worried there for a moment. But it sounds like this is actually a non-problem. We can carry on working on the important stuff – technology will bail us out here in time.
Dr. Jubjub: Sir! We already have the technology to fix the toves. The most straightforward way would be to whiffle their tulgey wood but we could also...
Prof. Bandersnatch: What?? Whiffle their tulgey wood? Do you have any idea what that would cost? And besides, people won’t stand for it – slithy toves with unwhiffled tulgey wood are a part of our way of life.
Dr. Jubjub: So, when you say technology will bail us out you mean you expect a solution that will be cheap, socially acceptable and developed soon?
Prof. Bandersnatch: Of course! Prof. Jabberwock assures me the singularity will be here around tea-time on Tuesday. That is, if we roll up our sleeves and don’t waste time with trivialities like your tove issue.
Maybe it’s just me but I feel like I run into a lot of conversations like this around here. On any problem that won’t become an absolute crisis in the next few decades, someone will take the Bandersnatch view that it will be more easily solved later (with cheaper or more socially acceptable technology) so we shouldn’t work directly on it now. The way out is forward - let’s step on the gas and get to the finish line before any annoying problems catch up with us.
For all I know, Bandersnatch is absolutely right. But my natural inclination is to take the Jubjub view. I think the chances of a basically business-as-usual future for the next 200 or 300 years are not epsilon. They may not be very high but they seem like they need to be seriously taken into account. Problems may prove harder than they look. Apparently promising technology may not become practical. Maybe we'll have the capacity for AI in 50 years - but need another 500 years to make it friendly. I'd prefer humanity to plan in such a way that things will gradually improve rather than gradually deteriorate, even in a slow-technology scenario.