Part of the problem, of course, is that the issue is extremely complex and messy. We should expect data to be uncertain with regard to a great many details, even if the underlying theory is sound. Worse, the popular press, politicians, and advocates have simplified this down to a shouting match in which identification of real data is extraordinarily difficult to locate for the average busy person.
What's troubling me is that most of the debate on the urgency of climate change is correlational rather than causal. The polar caps are melting, average temperature is climbing, all with the rise of green house gasses. What persuaded me earlier on is that the underlying theory appeared to match the correlation, increasing the likelihood that the outcomes are predictive rather than simply coincidental. This was the case with CFCs and the ozone layer, and acid rain and sulfur emissions. Even better with the last two phenomena, the reduction in the production in CFCs produced the predicted result: the hole in the ozone layer stopped growing and started reversing itself. A similar result has obtained -- to a more limited extent -- with reduction in sulfur emissions. Reduce sulfur emissions, reduce the acidity in local rain.
Climate change is a far more complex phenomena, with changes in one part of the world having potentially significant and unanticipated impacts elsewhere (e.g., the warming of the ocean reducing the Gulf Current and slowing the "conveyor belt" of warm air to Europe, causing colder winters in England).
Critics of global climate change are pointing to phenomena that seem to blatantly contradict the existing models -- notably recent trends in global ice caps stabilizing. As always, complex phenomena have variations and the data of a few most recent years is not necessarily indicative of a genuine reversal of an overall trend in conformance with the predominant models. Still, it does suggest that we may wish to be cautious in reliance on existing models. For one thing, previous models are based on an understanding of existing systems. Not only are these understandings necessarily imperfect, the systems themselves change in response to the new equilibrium and thus require reexamination of underlying models and predictions as new variables manifest.
In the short term, it shouldn't make much difference to practical behavior. Reduction of carbon footprint and a shift from fossil fuels offer a wide range of advantages regardless of whether we are, in fact, approaching a tipping point that will lead to the most pessimistic scenarios. In the longer term, however, we should be prepared to constantly reevaluate our understanding of the environment and our impact on it.