* seeding the ocean with iron filings to stiumlate growth of CO2-converting algae.
* floating reflective matts on the north pole, should the ice cap wholly melt.
* atmospheric processors, a la Kim Stanley Robinson's Red Mars
* scattering ash on the ice caps (to the opposite end), back in the 1970s when worries were about globalm cooling.
ps - please hold off the climage change opinions. there's so much of that already here. just curious about how far this thinking has gone.