The internet allows anyone, even those who don’t know the first thing about what they are writing, to advocate their pet hypotheses. Sadly, erroneous ideas are too easily repeated as though facts by others to perpetuate misinformation; the more repetitions, the more easily one finds wrong ideas when surfing. This is why many academics, self included, do not allow their students to use sources other than the primary literature: the web is replete with dangerous misinformation. Such misinformation is the fodder for Holocaust deniers and all other manner of obscenity; a Lethbridge professor is currently using the argument that the internet is factual as support anti-Semitic rants. The internet is not factual evidence; it is an un-policed repository for whatever anyone want to put there. As another illustration of the danger of the internet, check the credentials of deniers of global warming. You will almost certainly find someone who has done a bit of surfing, and even more likely has not bothered with consulting the scientific literature.
Skepticism is a healthy expectation in science and other academic disciplines. And we should not abandon skepticism, but we should also not emphasize skepticism over overwhelming consensus, because costs to us now (i.e., more severe weather such as recently in Sydney, etc.) from global warming (NASA 2016) are already mounting faster than we are exposing the folly of deniers of global warming. By overwhelming consensus, I mean that 97.1% of climate scientists (i.e., only people with credibility on the topic) agreed that global warming is a fact (Cook et al. 2016; and for fun, check out this video). You will rarely find this degree of agreement in any field of science! Perhaps you don’t trust scientists or NASA; if so, you probably are also skeptical about us having put people on the moon, or probes in the farthest reaches of our solar system. I will trust NASA long before I trust an untrained denier of global warming. In any case, skepticism about global warming has taken the most distant back burner; this is why virtually every government in the world is actively and aggressively working to address the problem. They know it is the right approach.
Is CO2 partly responsible? According to climate scientists, it is. Does it matter that CO2 makes up <0.04% of the atmosphere was CO2? Think about this; how much botulism toxin do you need to consume before you die? The answer is 0.000000013 g will kill you. In other words, it’s not the absolute amount that’s important, it’s the magnitude of the effect of each bit.
A bit of history. What happens when controversial ideas are first presented? Ever heard about how Copernicus suggested that the Sun didn’t revolve around Earth? Famously, even Galileo had to recant his support for this. Have you met any credible folks that suggest that the sun revolves around the earth? Have you met any credible folks that believe that the earth is flat? Skeptics also proclaimed that humans would never be able to build a machine that could fly. The pattern repeated, ad nauseum, is that no one believes an idea initially, then a few do, then many, then all the credible individuals do, and eventually nobody cares about the doubters. If an idea is correct and stands up to rigorous scrutiny, as have ideas about global warming (which incidentally dates back to 1896!), credible skeptics fall away, and the history of examples above show that poorly informed hoax advocates will eventually fade into obscurity. We’re at the latter phase for global warming.
Let’s take solace in the history of deniers. As George Santayana (1863) said “Those who cannot remember the past are condemned to repeat it.”
Cook, J., Oreskes, N., Doran, P.T., Anderegg, W.R., Verheggen, B., Maibach, E.W., Carlton, J.S., Lewandowsky, S., Skuce, A.G., Green, S.A. and Nuccitelli, D. 2016. Consensus on consensus: a synthesis of consensus estimates on human-caused global warming. Environmental Research Letters 11(4): p.048002.