Question

The greenhouse effect is a result of

Answer 1

Do you have choices?

Answer 2

cow farts.
oh, and cars + many other things that emit GHG

Answer 3

the first thing you need to know is the difference between greenhouse effect and global warming
greenhouse effect is essential to the Earth, keeping it warm, so it is suitable for living things to inhabit while additional CO2 or other greenhouse gases emission is the cause of global warming
CH4 (methane, e.g. cow farts) is one of the most renowned GHG

Answer 4

this further explains the cause of greenhouse effects and global warming http://www.livescience.com/37743-greenhouse-effect.html

Answer 5

so greenhouse effect is actually the result of the thin gas layer (atmosphere) that traps heat in the Earth(so the Earth is warm enough) and reradiate solar radiation (so the Earth will not be too hot)