This, is a very easy question to answer. The answer below isn't quite correct, there are several things you can do, just simple steps, to reduce the effects of Global Warming, for instance, donating towards charities in aid of Global Warming, charities aiming to plant more trees to reduce carbon emissions, to reduce electricity in other facilities, even to hand out flyers, making a point of it. You can also do things yourself, simple things, such as, not leaving a light on when not needed, turning off the computer when done with it, turning things off at the switch while not used. And, possibly the best thing you can do, is to use your bike, where you can, or, take the train or bus, where, more people in one transport, means, less transport, less emissions.
You can't reduce global warming at all. And if you made any serious effort to do so, it will destroy the world's economy. But, fortunately, you don't have take such drastic steps. Global warming, if it's happening at all, is not caused by mankind. And even if it is happening, and even if it is caused by mankind, it is, for the most part, a good thing.