This olivine solution doesn't really look any less viable than CO2 scrubbers, if I'm being honest.
Geoengineering is on the table now not because it is an easy shortcut, but because the world has failed to do enough in other ways. It's better for patients with prediabetes to change diet than develop full blown type 2 diabetes, but if diet doesn't change fast enough it's better to prescribe insulin than just let them die. Industrial civilization has discounted decades of warnings about changing its energy "diet" and will soon need more drastic measures.
I'm a little optimistic because renewable energy has become cheaper faster than I expected. I'm pessimistic because the world still isn't reducing fossil use fast enough (or at all, really -- so far the best news is "the percentage growth rate is slowing.") Even when the economics start to favor non-combustion energy sources, legacy fossil industries have often delayed the transition by obtaining government support to resist the economic pressures. So I believe that the world can transition to low-emissions energy but I also believe that it's not happening fast enough.
Even worse, the climate perturbation from anthropogenic emissions can trigger a dangerous positive feedback loop that will release even larger quantities of GHGs from natural stores as forests burn more frequently and permafrost thaws. I think that if people get the problem under control (as opposed to just suffering the effects, with no softening of the blow), it's going to involve 3 major prongs:
- Transition to non-fossil energy sources
- Geoengineering via solar radiation management, as a temporary bandaid to prevent runaway warming feedback
- Geoengineering via enhanced silicate weathering, as a thermodynamically stable fix for the excess CO2 added to the environment
Solar radiation management can be phased out as atmospheric CO2 levels drop. But with silicate weathering alone, I fear that thawing permafrost will outpace even the most ambitious CO2 drawdown efforts.
The second two prongs are still highly controversial and advocating for them tends to get one lumped in with climate denialists. I think that most people concerned about climate are going to come around eventually, though. The IPCC already has. We clearly aren't going to avert feedback loops by 2030 via emissions-reductions alone.
Here's one of the more optimistic studies I have seen about forestry-based approaches to curbing CO2:
The authors estimate that afforestation and other positive land use changes could provide up to 37% of the CO2 reductions needed through the year 2030 in order to stay under 2 degrees of warming. The other 63% has to come from elsewhere.
Now we have reduced forest cover and burned underground carbon. Reforestation only solves the former.
It's just bad enough now that forestry is no longer a valid option on its own.