global warming is a scientific theory that states that energy (which in fact can never just be destroyed and disappear, it has to go somewhere you know) from the sun, or cars, or street lamps, or just basically almost anything, is just sucked into the ground and the temperature of the earth slightly increases. another theory of this ilk is that one day, millions of years from now, the earth will be destroyed from something called the "heat death". this is just a theory, so you can decide wether to believe it or not.