What is the evidence that human activity and CO2 are the primary cause of the global warming over the last century? Is there any evidence that human's aren't the cause? What is the cause?
The science is trying to determine how much human activity and CO2 has contributed to warming. Same as above. Lots of things and modellers, physicists, chemists etc. are tearing there hair out trying bring all the pieces together. Scientists who are actively conducting research into climate science can only agree on 3 facts (meaning its' actually occurred and is verifiable) simply; Average global surface temperatures have increased in the past 100 plus years. CO2 has an infrared emission spectra. CO2 has been added to the atmosphere by humans. That’s really about it when it comes to verifiable facts on the main topics of climate science!
The stratosphere is cooling. The amount of longwave backradiation coming back down from the sky is increasing. The amount of longwave radiation exiting the atmosphere in the greenhouse gas absorption bands is decreasing. Those are smoking guns for greenhouse-gas caused global warming. They are all direct measurements, not models. No "natural cycle" or "it's the sun" theory explains those measurements, hence all such theories are wrong. We also know the "natural cycles" theories are wrong because the natural factors are trying to cool the earth, and had been doing so for the past 6000 - 8000 years. The sudden fast warming goes directly against the natural cycle, hence it's not part of the natural cycle.
I think the "man made" label is inaccurate as climate change would happen in the absence of humanity. I think a better label would be human hastened climate change. Some of our industry and technology create an unnatural source of pollution that at some level has a negative impact upon our climate. I am not sure if we can quantify the impact and defer to those who know more than I on that front. Anecdotally when I see smog from a major city drifting far from the city center, I find it hard to believe that said smog has zero negative impact upon our climate.
It may the issue is that nobody can say with any degree of accuracy when or by how much or even at all.
