The main problem is that there is a certain amount of polarisation in the positions—how else can one possibly describe the "climate deniers" label (without using a goodly number of swearwords)?
So, let me try to explain some very fundamental points about this particular debate...
- Climate change
No one really believes that the climate is entirely static; it quite obviously isn't, or we wouldn't have seasons or ice ages. Or, for that matter, the Mediaeval Warm Period and Little Ice Age.
The climate changes, that is a fact: the question is, what makes it change?
Are these changes—indeed, can these changes—be triggered by human activity? If so, to what extent and, if these changes are significant, are they good or bad?
If these changes are both significant and bad—for given definitions of "bad"—then how catastrophic are they? Do they threaten the existence of our species (or others)? or are they just mildly inconvenient?
And how catastrophic are these changes, in terms of allocating our scarce resources? Is it better to mitigate or to adapt?
Sensibly, all of these questions should be answered. Where a mechanism of change is encountered, then data should be gathered to test the hypotheses.
So, what do we know?
Well, actually we know extremely little.
We know that the Earth has been both considerably hotter and considerably colder in the past; it has also been very slightly hotter and very slightly colder.
We do know that when a very slightly hotter period became a very slightly colder period, then millions of humans died.
But, the problem is that we can't actually take tremendously accurate readings because there were no instruments to do so. We also know that, even where we try to reconstruct temperature series with proxies, our picture of the plant's climate covers a very short period of time geologically and is, not to put too fine a point on it, woefully inadequate.
Even where we do have direct measurements, we don't know how accurate those are. If you were to believe surfacestations.org—or, indeed, Anthony Watts's so-to-be-published paper—then there may be significant problems with this surely simple data set.
Thus, one of the main problems is that we don't really know whether there has, actually, been any significant warming over the last century—we think that it has been about 1°C but we are not really certain. Not least because the scientists don't seem to be tremendously good at understanding statistical analysis.
We do think that the increase in CO2 emissions by humans over the last century has the potential to increase global temperatures through, for instance, well-understood theories such as the Greenhouse Effect. But we don't know to what extent CO2 actually affects the climate through that mechanism.
Nor do we know what feedbacks are inherent in the system: or whether they are positive or negative.
In short, we don't know much—except that we are spending billions of pounds a year on trying to fund a mitigation solution to something that we don't even know is a problem.
I intend to pick up this baton again, but let's be clear—we are arguing questions of degree here, not absolutes.