To be quite honest, I was never really fond of the man, but ever since he quit his executive positions at Microsoft, I'm starting to like him more and more. The reason is not that he's giving money away, but the causes he's giving the money for. I'm not really sure how practical this idea is, but if it has any chance of becoming reality, it's definitely worth looking into (plus it's the first time I've read about such a thing).
The first trials of the controversial sunshielding seem to come at the right time, as the UN failed to secure an agreement on cutting greenhouse gases. The American and British researchers are not going to wait for an international law to pass (which, the way things are going, is not going to happen tomorrow) and see gas emissions levels rise to the sky.
Instead, here's what some of them have planned: machines that basically suck up 10 tonnes of seawater per second and throw it in the air, to form white clouds and help reflect the Sun's rays away from Earth. There have been numerous proposed methods of technologically cooling our planet, but according to an efficiency study, this is among the best candidates. It's estimated that the ships needed to manage such a task would cost only £5 billion. However, the atmospherical consequences are still up for debate, with both sides coming with good arguments. I haven't been able to get some good documentation though, there just doesn't seem to be much information about this, but it seems to be a really interesting project nonetheless.