A few extra details to add: The greenhouse effect is said to occur due to gases absorbing some of the infrared radiation that would otherwise be emitted out into space by the earth. Earth's temperature is mostly determined by its distance from the sun, as this effects the energy received by the sun, and will change the temperature where emitted radiation from the earth will equal the absorbed radiation from the sun. Effects like clouds, snow, greenhouse gases, etc. will change this temperature by absorbing and reflecting different amounts of radiation that would otherwise either be completely absorbed or completely emitted.
Any gas that absorbs infrared radiation will have some sort of greenhouse effect, since they will absorb energy that would otherwise go out into space. This most likely includes any sort of gas that has different types of atoms in it, (A bit from physical chemistry last semester: any gas that can change its dipole moment in vibrations will absorb infrared radiation of some sort, which in general seems to mean gases with different sorts of molecules in it. Whether this fully applies to absorption in the atmosphere is up for grabs, or whether some other effects come into play, but it overall makes sense on hearing which gases are greenhouse ones.)
How is that egotistical? They're giving a rational explanation for why the earth is heating up (an unlikely one, but global warming is unlikely so...)
I was saying the egotism comes from the fact that people think they're so powerful... got nothing to do with figuring it out, I just think people want to think that they're in control.
First off, global warming effects do have support from the way that Venus is hotter than Mercury, despite being farther away, and perhaps also from the fact that earth's temperature stays around the amount where it would be if it absorbed all energy from the sun and reemmited it perfectly. (Otherwise, earth has plenty of snow, clouds, etc. to reflect energy back into space.).
Secondly, people already have large scale effects just from day to day living in other areas (desertification, "heat islands" near cities, helping to make the "fertile crescent' much more barren today, various extinctions/near extinctions, forest reduction, etc.). It's not too much a leap to guess that people could be effecting the entire planet in some way based just off of everyday activities adding up.