I don't think we will ever see 5 degrees of warming if sun-reflecting particles work, and chances are they do.
The ocean is the easiest effect to prove, but then there will be other unknowns of altering the air to have more CO2 and a dimmed sun.
You’re awfully cavlier about the one inhabitable planet we have.
I agree that there are big unknowns but I don't think that detracts anything from the point I'm making.
But that still leaves us with the other symptoms (ocean acidification) and unknown side effects.
So it's not a cost benefit analysis, because it only looks at the known costs. Here the known downside of an acid ocean and the unknown cost of side effects dwarf the actually calculable financial costs.
If we could run a thousand earth simulations we could speak of cost benefit analysis. But we just have one, and we know the conditions we grew our civilization in.
We may well have to do sun shading regardless, but we shouldn't call it a mere ten billion.
Edit: I guess to more properly respond to your original point: things may get very bad even if we do sunshades. Just via other mechanisms. Having the option will likely encourage a much higher co2 level than without sunshades.
Seems to indicate most of our food would be fine without pollinators. We would lose tree fruits, berries (but not grapes), and melons. Nightshades would become more work, and everything else is pollinator optional.
I have heard that orange groves have humans pollinating them in many cases, so we might not lose all tree fruits either.
As is sometimes said, the battle is in the mind.
We are facing a food crunch in the near future- we will number 9-11 billion before population declines begin to set in at the same time climate change will be desertifying the worlds breadbasket, we are running out of fresh water, we are running out of top soil, and insect declines will threaten the angiosperms we eat. It is not clear how insect populations will respond to the 3-5 degrees of warming expected by the end of this century (based on RCP 8.5 and RCP 6.0 from the latest IPCC report).
Mid-century is shaping up to be one of the most important and tragic periods in human civilization, if it is to survive it. We should keep in mind we are always nine missed meals from anarchy.