The good professors are laying on the qualifiers because the field of geoengineering aims to do nothing less than to change the climate of the entire Earth in an attempt to stave off the negative effects of global warming. As we discussed earlier, geoengineering is basically an attempt to hack the climate. Based on observations that volcanic eruptions can have a temporary cooling affect on global temperatures as volcanic dust shot high into the atmosphere reflects some of the sunlight falling on Earth back into space, geoengineerers proposed shooting massive amounts of sulfate particles into the upper atmosphere to reflect a portion of the sunlight on a global scale. The idea is that if the amount of sunlight hitting the Earth's surface is reduced, the resulting drop in temperature will offset the global rise in temperature due to the growing amounts of greenhouse gases in the atmosphere, which prevent heat from naturally radiating off into space.
Sounds simple, even logical, right? Sure, except for the fact that it is the worst idea in the history of mankind. Geoengineering has a few flaws. For one, there's the matter of this slight potential side effect: a permanent whitening of the skies. Those particles meant to reflect some of the sunlight, also will likely diffuse it, meaning the sky will take on a white, washed-out appearance; in other words, so long blue skies... An even bigger problem is that once you start geoenginnering in a large scale, you can never, ever stop.
The reason is simple: geoengineering doesn't reduce the amount of heat-trapping greenhouse gases being pumped into the atmosphere, it just tries to offset this gain with a corresponding reduction in temperature on the other side. Those sulfate particles will eventually settle out of the atmosphere, meaning more will continuously have to be pumped in to take their place. Stop pumping and the cooling side of the geoengineering equation goes away, leaving you with a runaway greenhouse effect that will cause global temperatures to spike upward.
Unfortunately, this crackpot idea has attracted the backing of some serious (and seriously rich) people like Bill Gates and Richard Branson. But let's remember we've gotten ourselves in this greenhouse gas mess by pumping a lot of things into the atmosphere that shouldn't be there, pumping more things in at this point seems like a pretty bad idea.