Molecular manufacturing will give us the ability to do planet-scale engineering. We may need it.
Polar ice is melting faster than expected, and permafrost is releasing methane. Science tells us that large-scale reduction in atmospheric carbon dioxide may be necessary to avoid major, destructive, near-irreversible climate shifts.
According to a recent CNN news story on carbon capture technology, it may be possible to remove carbon dioxide economically with today's technology. A machine that costs as much as a car could remove the carbon emitted by 20 cars. The power required to remove and liquefy CO2 is 1/5 the power generated by burning coal to produce it.
Of course, removing CO2 is only part of the puzzle. There remains the question of what to do with it. There are several possible answers to that, and it remains to be seen which one is best.
I'm enough of a pessimist to think that this technology will not be adopted until it's too late for it to make much difference. Thus, instead of (for example) a 5% tax on cars to offset their carbon emissions, we'll need a massive crash program. Today's technology will just be a reminder that we don't use technology wisely.
When molecular manufacturing was proposed in the 1980's, there were many applications that could not be achieved by any other technology. As time goes on, some of those applications are being addressed by advances in other fields of technology... at least potentially. Understanding the uses, misuses, and non-uses of today's technologies gives us some clues about how molecular manufacturing may be used and abused.