One way to combat global warming is for us to stop emitting greenhouse gases. Really, it's the best way. But if we can't make that happen, Plan B is to just zero out artificial global warming with artificial global cooling, and an ambitious test involving giant balloons spraying water is about to take place off the coast of Britain.
A relatively easy way to cool down the planet would be to send some of the solar energy Earth gets exposed to back out into space. The ice caps (being white and reflective) do a good job at this, but they're not big enough (and shrinking fast), so British researchers have come up with a reflective chemical substitute. The idea is that they'd spray massive amounts of aerosols into the upper atmosphere (about twelve miles up), where they'd reflect enough sunlight to make a dent in global temperatures.
To get these chemicals up to where they need to be in bulk, the SPICE Project (Stratospheric Particle Injection for Climate Engineering) has settled on tying what is effectively a very very long garden hose to a very very large balloon, sending it up into the stratosphere, and then pumping chemicals up the hose and out the top where the balloon is. To test out the concept, a small scale experiment has been scheduled involving a balloon that goes up only a little over half a mile, with a hose attached to it that sprays water. If it goes well, a full-scale test (involving a balloon that's 600 feet wide lifting a few hundred tons of hose over 10 miles into the air to spray actual chemicals) could come next.
As you might expect, lots of people are saying that this is an utterly crazy idea. And it's true, nobody wants to have to resort to such drastic measures. But the SPICE Project says that what they're working on really is just a contingency plan, in preparation for the unlikely event that governments and industry don't manage to drastically cut their greenhouse emissions as fast as they need to, to keep us all from frying to a crisp.