Correct, water scarcity is in fact the PRIMARY bottleneck.
The main "innovation" in this solution isn't "we must plant massive forests," it's that clean (solar-powered) desalination is now possible at very large scales, so we are able to provide the volumes of freshwater necessary for large-scale reforestation and conversion of deserts.
Forestry people have known for decades that trees were the best solution to CO2 in the atmosphere, but there wasn't enough forestable land. And while we can reclaim deserts, we couldn't do it at scale unless we irrigate. And we couldn't do it unless we could affordably create a new source of freshwater that wasn't already needed for humans and agriculture.
Should also mention that water requirements are generally much higher than needed to sustain an existing equivalent forest, as most desert soils have a high salt content near the surface, due to evapotranspiration drawing salts up and concentrating them, and lack of precipitation to ever flush/dilute them.
Not sure if any of these proposals plan to attempt to actively reduce soil (or aquifer) salt content, but for basins without sufficient excess water for an outflow, salt build up is a big problem. Managing the salinity requires more fresh water than what is needed to sustain the plane life.
The main "innovation" in this solution isn't "we must plant massive forests," it's that clean (solar-powered) desalination is now possible at very large scales, so we are able to provide the volumes of freshwater necessary for large-scale reforestation and conversion of deserts.
Forestry people have known for decades that trees were the best solution to CO2 in the atmosphere, but there wasn't enough forestable land. And while we can reclaim deserts, we couldn't do it at scale unless we irrigate. And we couldn't do it unless we could affordably create a new source of freshwater that wasn't already needed for humans and agriculture.
Now we have it. Now the solution in possible.