Another name for biochar is tera petra and it may well be a soil super substance (at least the pre-contact Amazonian cultures thought a lot of it).

We’re already creating clouds mechanically via aircraft contrails that act as clouds globally. The scary thing about these is that they’re suppressing global temperatures by a significant amount, as shown in this paper: http://facstaff.uww.edu/travisd/pdf/jetcontrailsrecentresearch.pdf. Fewer planes in the air during the day boosts temperatures significantly and quickly (within days). But this shows that boosting albedo does have an effect and would work if only there were ways to do this that didn’t have really nasty unintended consequences.

After all, jet travel produces large amounts of CO2, dumping sulfur dioxide into the air destroys ozone, and we have no clue what the effects of pouring that much salt spray into the air will do over the long run. It’s an interesting enough idea that it’s worth more study, however, and maybe a couple of demonstration projects as well.

After all, sometimes the only way to understand what the consequences of doing something are is to test it at small scales.

It basically means using ocean water to mechanically create clouds since those types of clouds would have higher albedo (reflectiveness). AKA, manufacture sea salt spray to change the way clouds form over the ocean to increase their reflectivity.

There are a ton of different geoengenering schemes out there to lower global temperatures. The journal Atmospheric Chemistry and Physics did a cost/benefit analysis of a bunch of them; with the cost being the amount of watts it took per degree of global temp reduction (the benefit).

Of course, you’ll need to make your planet-saving decisions on more than just energy input costs, but it is good to see how effective each is when compared to each other. For instance, biochar, which you mentioned above, gives you much more bang for the buck than fertilizing our oceans. But both are dwarfed by cloud seeding. And then you’ll have to think about all of the unintended consequences, reversibility, and ability to be tweaked each approach gives.

And then of course there are the really crazy ideas, like huge water sprays and three mile high chimneys.

It will be fun to see what approaches the world rallies behind in the coming decades.