How can we reduce global warming?

reducing your electrical consumption should also do the trick because the power generating plants are mostly making C02.

use catalytic converters in car exhausts.

don't cut trees because the trees can absorb the Co2 and prevent pollution in the air

 
well, the main gas that is causing it is CO2, i guess it could be reduced if we could produce more electric-powered or solar-powered vehicles. Also in many factories,etc, large amounts of NO, CO2 and SO2 are produced, which will pollute the air, so maybe burning with different chemicals might help. There's also the problem in the stratosphere, many ozone molecules are breaking apart into oxygen molecules, the main problem is to get rid of the oxygen atoms (though i have no idea how to do that)
The only thing a high school student can do is try to keep the environment in order.