Well, Al Gore said in 2008:
http://www.youtube.com/watch?v=MsioIw4bvzI
that the entire north polar ice cap would be melted by 2013. We have eleven more months to see whether this prediction turns out to be true or false. That's a testable prediction. We can put it to empirical test and see whether it's true or false. PROTIP: the north polar ice cap was still there, at last observation.
If you don't have testable predictions, what you have is called "opinion," and like assholes, everyone's got one but they don't produce anything very useful.
Scientists publish their data. Scientists don't have secret computer models nor secret data. Scientists don't say "We also have a data protection act, which I will hide behind," "I'm getting hassled by a couple of people to release the CRU station temperature data. Don’t any of you three tell anybody that the UK has a Freedom of Information Act," "I think we have to stop considering 'Climate Research' as a legitimate peer-reviewed journal. Perhaps we should encourage our colleagues in the climate research community to no longer submit to, or cite papers in, this journal."
Science is mathematical modeling of reality, empirically constrained. Science strives for spareness of form with maximum generality. Science discards models which make predictions not borne out by reality.
If they can't predict whether it will rain in two weeks, why should we believe they can predict what the temperature will be in two hundred years? And how could we test it anyway, given that neither of us is likely to live long enough to read the thermometer when the day comes?
Speaking of global warming,
http://www.dailymail.co.uk/sciencetech/article-2093264/Forget-global-warming--Cycle-25-need-worry-NASA-scientists-right-Thames-freezing-again.html <-- oops
http://www.theregister.co.uk/2012/01/30/wsj_global_warming_letter/ <-- People are beginning to say publicly that the Emperor has no clothes.
>What would it really take to convince you? A prediction of future temperatures? Remember, it's average temperatures over many years that matter. And numbers are never persuasive.
Until "climate scientists" present empirical proof of their radical and alarming claim that Ragnarok is upon us unless the entire human race goes back to the caves right now, the null hypothesis holds. And it really is that simple.