Question

How is the greenhouse effect related to global warming?
PsyDAG
Earth's natural greenhouse effect is critical to supporting life, and initially was a precursor to life moving out of the ocean onto land. Human activities, however, mainly the burning of fossil fuels and clearcutting of forests, have accelerated the greenhouse effect and caused global warming.
oobleck
The greenhouse effect is the tendency to retain heat from the sun, due to the buildup of various greenhouse gases in the atmosphere.

The various causes of global warming are still being studied. Do not be tempted just to say human activities are the cause of global warming, and leave it at that.