How do we know the increase in CO2 is human caused? There is an isotopic signature, like a fingerprint. CO2 that comes from natural sources has a low carbon-14 ratio. The pre-industrial atmospheric levels of CO2 were around 280ppm (parts per million). As of 2010 the amount is 390ppm. The extra 100ppm does not have the carbon-14 signature. The only other possible source that can account for the extra 100ppm is human industrial emissions of fossil fuels.—Open Source Systems, Science, Solutions Foundation What is the cause of global warming? Global warming is occurring because humans use unprecedented amounts of carbon-based energy sources such as coal, gasoline, and natural gas.—Amy Farrar, Global Warming.
1. In a causal argument, the conclusion can be questioned because it is the claim at issue. But in an explanation, the claim being explained is assumed to be true. Since there is no conclusion to question in a causal explanation, what can you question?