Well, the evidence that CO2 levels are rising is inarguable. Nobody disputes that, since it’s easily measured and recorded.
What impact CO2 levels have is somewhat arguable. As this article says, “‘We really don’t know how high CO2 has been in the geologic past. Thus we don’t know how sensitive the surface temperature of the Earth is to CO2,’ said Don DePaolo, head of the Earth Sciences Division at the Lawrence Berkley National Laboratory in California. Most global warming predictions are based on fluctuations in CO2 levels and temperature that happened between a relatively recent series of ice ages.”
If you go by what’s known about recent ice ages, the correlation between CO2 levels and surface temperatures is tight. There is some (probably minor) chance that those recent ice ages produce a false correlation, though.
The other issue is whether the rising CO2 levels are partly or wholly human-caused, or merely naturally occurring. To me, it seems highly unlikely that this spike in CO2 just randomly happened to overlap perfectly with the Industrial Revolution and its accelerating burn of CO2-emitting substances.
So, whether you “believe” is really the wrong question. The question is where you place the odds, based on the evidence. Personally, I see it as 90 percent chance that GW is happening, and another 90 percent that it is largely human-made. So .9 times .9 is .81, meaning I think there’s an 81 percent chance that the scary story is accurate.
Of course, the other issue is the attitude to risk one thinks is proper. Unless you think there is strong evidence that global warming is either a complete hoax or is real but holds zero percent chance of causing serious problems for the future, then you have to adopt a responsible position on it, if you wish to practice elementary ethical behavior. To me, the choice is between assuming it’s fake and/or won’t cause big problems, and assuming it might. If it might, then the next question is what to do about it.
Is it not the height of recklessness to refuse to acknowledge a possibly immense risk to one’s (and other people’s) children and grandchildren? Is it not the height of irony that the ones who are doing exactly that are also the ones who claim to stand for “values?”
Meanwhile, the other, possible more pressing environmental catastrophe is peak resources. Personally, I think the odds of encountering huge problems, soon, stemming from that are 95%. Yet, it is entirely suppressed by the media and mainstream politics. Why? My analysis is that it is indeed less debatable, both at the level of evidence and required solutions. And the required solutions include a cessation of capitalism.