20 Bold Schemes to Save the World

Some of these are pretty cool, my favorites:

2. A Giant Artificial Stomach That Eats Seaweed
Step One: Grow lots of kelp near the surface of the ocean. Step Two: Harvest it and “digest” it in a giant plastic “stomach.” The giant green mass gives off lots of gas — the CO2 could be siphoned off and put in some dark place and the methane could be used for powering humanity’s myriad doohickeys and gadgets. So it’s a twofer, removing carbon from the atmosphere and creating an energy source.

9. Huge Solar Farms in the Sahara
A relatively small piece of the Sahara could theoretically provide electricity for the entire planet if it were covered in solar thermal mirrors. Plus think of all those jobs to build a solar plant the size of Britain. The
new transmission grid would be quite a project as well

I'm not sure that any of these are remotely feasible, but interesting nevertheless.