At least one serious proposal in this regard are neither globe-spanning nor likely to lead to any unintended consequences (esp. since it is easily reversible): the aerosols would be introduced by adding sulfur content to the jet-fuel of planes flying over and near the Arctic (as many do on great circle routes). It would have a cooling effect like volcanic eruptions, could be stopped whenever needed, would be concentrated in the one place that actually has been warming significantly and with possible dire consequences, and works whether the cause of the warming in the Arctic is greenhouse gasses (not likely since that mechanism doesn't produce the observed asymmetry between Arctic and Antarctic), soot from coal burning in China, Russia and India (my favorite theory since it does explain the asymmetry) some natural cause, or a combination of all three.
Funny thing about air. It doesn't just sit there, it moves around. Volcanic eruptions gave us the year without a summer, and other events which, while short lived, had dire consequences for humans.
The planet has done just fine regulating its temperature without us mucking about with it. We aren't even certain of the source of warming at one pole, and tinkering with the weather in what will amount to an entire hemisphere might not be the best idea. If you remove all the adjustments from the last 18 years of data which I strongly suspect were done, not for accuracy, but to keep the meme alive, the curve comes out flat.
Weather data gathering stations have been surrounded by development, and the urban heat island effect may well be giving us readings which are too high.
At any event, even if all our recorded data are taken at face value, we do not have a significant segment to predict with. There is no horrifying trend toward planetary immolation, we have the technology to adapt to the temperature changes without tampering with the planet, so let's leave it the heck alone and see what it will do on its own.
