The basic problem most of the people paying attention have with the Anthropogenic Global Warming idea is that it is formatted as a conjecture. In science, you have a formal process for establishing the level of credibility of ideas. You can never claim Truth, with a big T, but you can state that a given equation or prediction has without fail performed flawlessly in all efforts to disprove it.
This last is important. A fundamental notion in science is that of falsification. If you want to compare one understanding of the world relative to another–say the idea that our current temperature alterations are natural, relative to the idea that they are created mainly by human activity–then you need to format your hunch as a hypothesis. You say, “I predict that if my idea is right, then X will happen. If X does not happen, then my hypothesis is not the one that best fits the data”.
Self evidently, nobody likes to be proven wrong, but the reality is that that is how our sum of knowledge increases, so this is an essential component of honest science.
There is in fact a simple prediction made from the AGW conjecture, which made publicly would elevate the idea to that of a hypothesis.
The relative importance of CO2 on temperature goes up as you travel up in the atmosphere:
Given the present composition of the atmosphere, the contribution to the total heating rate in the troposphere (the portion of the atmosphere of most interest — it is the region from the surface to basically the top of the active weather zone) is around 5% from carbon dioxide and around 95% from water vapor.
However, in the stratosphere, the contribution is about 80% from carbon dioxide and about 20% from water vapor, although this makes a relatively small contribution to total greenhouse effect.
Therefore, the prediction can be made that if CO2 is responsible for most of the warming, that we will see disproportionate warming in the upper atmosphere–perhaps 2-3 degrees for every degree of surface temperature increase–which can be easily verified by satellite. Thus far, nothing has shown up, and this fact has been ignored or even suppressed. The models have been invoked as more accurate than actual measurements, which of course is highly unscientific and even unethical.
If the AGW proponents want to ask us to make enormous and economically damaging investments based on their ideas, they need to make them scientific. This has not yet been done.
I should close by saying this formulation is accurate to the best of my understanding, but I am not a climate scientist. I am verifying these ideas with someone who knows more than me.