Obviously the climate goes through cycles and there have been many global warming events (and ice ages) in the past. And I never said that human activity was entirely responsible for the current one.
But claiming that our recent release in the atmosphere—recent in cosmological terms—of millions of tons of carbon dioxide and many other greenhouse effect gases has no effect whatsoever is a blatant lie told by coal and oil producers, and by the governments of countries whose economy is based on them. The ability to put two and two together should be enough to understand that whatever enters a system affects it in a way or another.
You can always find scientific articles that contradict the others (especially in this case, because as I mentioned earlier, the US government and various oil companies have founded several allegedly independent researches during the last decades to make up proofs that human activity had no effect on the climate). That's why you should never base your claims on one research or another, but only on the international scientific consensus. And AFAIK, the consensus at the moment is that human activity has indeed a big effect on global climate.
Many people live by the Bible and believe that the Earth and everything on it were given to the human kind to do with them whatever they wanted. I don't mean to offend anyone, but this also is a lie (and please, don't bring up creationism). The Earth doesn't belong to us. We belong to it, like everything else that has grown on it. And as the (so-called) most advanced species, it's our responsibility to take care of it, not only for us and our grand-children, but also for the other species that have the same rights on it than us (most were here long before us, after all). But what do we do instead? We exploit everything that can be exploited, and we're now doing it at a rate that exceeds the system's capacity to heal and regenerate itself. This is stupid, and selfish, and closing our eyes on it is the laziest and most childish attitude we could have. Like "I can't hear you, lalalalala". I agree completely with what Smith says in Matrix: "The human species is the cancer of this planet".
And don't get me started on the ****s, whatever their age, who say they don't give a shit about what will happen after their death!