Since we are only allowed to discuss this topic on this thread, here's what I would propose (I'm not going to painstakingly go through each point and supply links, though; the info is out there and supported by what I say below):
1) Validate existing models: This, believe it or not, has not been done adequately to this point and has, instead, lead to many suppositions being stated as proven fact. For example, in the field (I won't use the term "science", because it hasn't been proven to be one yet) of dendrochronology, which has been used as one of the primary supporting methodologies to prove historical temperature records in regions, there has never been an adequate prospective confirmation of the methodology. In one example where this was tried (in southern France), this methodology was most definitively not validated. What should be done is that specific, representative sample trees should be randomly selected and data should be collected over several growing seasons against direct, high-fidelity measurements of temperature, humidity, sunlight, moisture, and a whole host of other growing conditions that can affect tree-ring size in a growing seasons. These should then be compared directly - in an experimenter-blinded fashion - with the actual side-by-side recordings of the same parameters by the calibrated recording equipment. This would then either validate or refute, or at the very least provide a reference range, of the methodology being used to currently support the statements of fact being offered by researchers using this methodology. A similar methodology could be used for snowpack accretion of carbon dioxide. To my understanding, this has not been done to date and, where it has been attempted, the data is woefully inaccurate. This, to me, renders the entire historical temperature record suspect or, at the very least, with a much wider variance than is currently being reported.
2) Provide open access to all data: Again, much of the reports published are being done so based on what is being called proprietary data. When people request this raw data for independent analysis, they are being refused. This should automatically raise red flags to anyone who wants to put creedence in the data. For example, imagine if a pharmaceutical company (with which I have direct experience) submitted a new drug application with a bunch of summarized data, but refused to give the FDA the raw data to review and verify. I can certainly tell you that the drug application would not be accepted for review, let alone the drug being approved. The same holds true here. There are researchers who are offering study reports stating that they've proven a particular "fact" about climate change, yet are unwilling to offer their raw data for their methodology and analysis to be reviewed. Red flag. And, much of these reports are subsequently included in the greater argument without the opportunity for individual validation (see point 1).
3) [Open, invite, encourage, and welcome a multidisciplinary approach: Currently, the field generally relies on so-called "experts" in climatology, who have demonstrated this only by their publications in their own field. This is a bit isolationist. Any broad field of science, and certainly this one is, should include and welcome open input from physical and applied chemists, mathematicians, biostatisticians, people with expert understanding of research methodology, and a whole host of other commenters (etc.) to improve and strengthen the rigorousness of their methods. To suggest - and worse dismiss off-hand without further consideration - that certain people are not capable of providing criticism because they are not an expert (i.e., climatologist) diminishes potential novel and insightful perspective on the data and the conclusions being drawn from that data. It is always best to have a lot of questions from a lot of different disciplines that form the basis of each individual aspect of the field. This provides opportunity to explain, clarify, and reinforce correct ideas, as well as re-visit and revise incorrect ones. This also offers an opportunity to teach as well as learn. For some reason, the current camp seems loathe to do this instead choosing to attack when serious questions are asked and valid points are raised, instead of acknowledging where there are holes and gaps in the current theory. There is a real problem when only one group of scientists are doing all the science. Most, at least the ones I've dealt with professional over the past 14 years, invite open feedback and help from other disciplines. Why not here?
4) Table the politics: For now, we have to tone-down the tenor of this debate and take it out of the public policy milieu. This has done nothing but caused a lot of resentment among individuals and served to polarize the issue. This could simply be accomplished by saying something to this effect: "We have observed what we perceive to be statistically and scientifically significant climate change over the past 2 decades. Based on this, we are now going to make [these predictions] about what will happen over the next twenty years. These will be 'set in stone' so-to-speak, and we will re-visit these predictions then and determine if we were right. If they prove to be true, then we will agree to make difficult changes at that time to the way we live our lives in order to remedy what will then have proven to be our clear, irrefutable impact on the climate. It will not be 'too late' to do anything at that point, and we still until that point arrives continue to discuss remedies and plans for change. We will, however, not attempt to mandate them at the international level until we are proven correct." This would allow ample time to prospectively prove the point. And, at the end of that timeframe, you'd have a lot less ability by the so-called naysayers to disagree. What you need is buy-in now, and most of us who question the current "state of science" are actually quite reasonable people, provided that "fair play" (as described above) is in place.
5) Consider alternate hypotheses: What if the world is warming and man is causing it, but it has nothing to do with carbon dioxide? This could certainly also be a possibility. But, we're so focused on one variable that we are almost blind to other possibilities. Researchers and the public need to be open to the possibility that other factors might be at play, and that carbon dioxide may be a minimal, if at all, causative agent. Or, it might be the sole causative agent. If so, let's set-up ways to definitively and prospectively prove this.
I think if these things could be done, we would have a much more meaningful, believable set of premises on which to discuss this topic and continue the debate.
-Dr. Imago