*yawn* damn you people for arguing in such an un-nice way while I was taking a nice long nap in preparation to respond!!! :steam:
and so you wanted a simple explanation Nocap?

I was prepared to give you a rather complex one if necissary!
Greenhouse gasses trap the heat from the sunlight closer to the surface of the earth, this makes the surface temperature warmer, which makes water evaporate at a higher rate, putting more water vapor in the air. Water vapor is also a greenhouse gas, which traps in heat... the cycle repeats itself over and over, getting incrementally warmer each time.
Why aren't we feeling this in most of the world? So far our oceans have been absorbing a good portion of the warmth that was added to the atmosphere and burying them thousands of feet below the surface (oceans, covering ~2/3 of the planet, are tricky things

) This heat will resurface again in the future when the deep ocean currents cycle up to the surface of the ocean. This is provided that the increased surface temperature of the earth really doesn't turn off the thermohaline circulation of the ocean and plunge the north atlantic back into a state of glaciation like in the movie Day After Tommorrow (though it would never happen that fast) - that scenario isn't as likely as the globe continuing to get hotter and the distribution of precipitation around the globe altering to make some of our most habitable regions inhabitable!
that's the simple explanation of what could happen because of what does happen- if you want the complex one just tell me!