We humans are right now conducting the experiment. Despite empirical evidence, data, modeling, and application of our knowledge the effects of green house gases we continue to pump them into the atmosphere on a massive scale. In another 30 - 40 years the experiment will yield conclusive results. Then I suppose global warming deniers like Rush Limbaugh will shrug their shoulders and say, "Well, we now have our experimental evidence."
I look forward to the results however I'm not sure they stand as an unbiased controlled experiment and are as factually devoid as the methodology.
Many things are observable but the difference between correlation and causation are somewhat more subtle.
Please note, I'm no denier and think that we should reduce our emissions as they have secondary benefits, fully acknowledge that there is a slight raise in global temperature but to assign a cause is a little premature.
Add to that the incidental political involvement, funding and the 'facts' (of incidentally we have none, nor many viable theories) leads to a logical conclusion that "mu" (neither yes or no) is a better stance to take.
The experiment isn't controlled, but it's being performed. The experiment is, "Let's dump gigatons of excess CO2 into the atmosphere and see what happens!" So far, what happens is that global temperatures go up noticeably.
What are you proposing we should do? Should we just ignore the whole thing until it's proven?
Not at all. I'm saying that we should reduce emissions. What could possibly be bad about that?
Its what I'm not saying that is important. I don't proclaim an answer nor an idealism, merely cautious scientific thought that suggests the methodology needs to be considered. In any other field the lack of rigorous proofs would be laughed off the table.
We don't know what other explanations there might be. Trotting out a limited number of counter-explanations like solar activity or volcanoes, and showing they don't explain the phenomenon, and therefore your pet explanation is true because it matches the data more closely, is logically specious.
We don't know the dynamics of the system. All we know is that for the data we have so far, the models work pretty well. We have no idea whether, in 200 years, these trends would lead to a 20 degree average temperature increase, a 0 degree increase or a 20 degree decrease by activating some unanticipated alternate environmental dynamic that plunges us into an ice age.
CO2 emissions as the cause of the recent temperature trend is plausible, and the results could be catastrophic, so I'm all for reducing emissions and taking every other practical measure we can to avoid the risk[1]. That's not the same as, "Anthropogenic global warming is settled science, deniers are morons, and if we don't do something now Earth in 100 years will be hell."
[1] I think the problem is, we can't agree as a society, or globally, how much we should do to mitigate it. We could spend lots of money directly, on solar power, nuclear power, electric car subsidies, etc. We could impose tremendous costs on CO2 emitting industries through regulation. But we can only speculate, based on a simplified economic model and assuming long-term accuracy of some environmental model, what the ultimate cost/benefit would be.
The science is settled, in the sense that the vast majority of people working in the field think this is probably what's happening. I think people who object to "settled" want it to mean "absolute certainty" but that's just a quibble over wording.
Deniers are morons. That's not the same as saying that there's no room for debate. There's always room for debate. But it's also a fact that the loud public face of the deniers is a bunch of politically motivated faith-based science illiterates peddling terrible rationalizations. Now, the fact that one side is full of idiots doesn't make the other side correct. But neither does the lack of complete definitive proof for one side mean that the other side isn't full of idiots.
And I've never seen anyone say that the Earth will be hell in 100 years. I have seen a lot of deniers say that this is said, in order to discredit climate change. What's actually said is that there will be a lot of disruption and chaos from changes, but of course there will always be lots of nice places to live, climate-wise. They just may not be where they are today.
Didn't Feynman say that the real measure of science is experiment?
Show me the experiments otherwise we have merely observations and conjecture.
They might be right, but at the moment we've established hypothesis and nothing more.