Climate change deniers like to impose impossible demands on the research of climate scientists. They home in on any uncertainties and they tend to exaggerate these uncertainties, at the same time dismissing probabilities and modelling as irrelevant. This allows deniers to manufacture uncertainty about the entire field1. This is the same sort of argument technique that creationists use; any gap in the knowledge of the history of life invalidates all of palaeontology, and therefore evolution.
Climate science is, like most sciences, complex, and as in most sciences, advances continue to be made. However, there are still many uncertainties and because of the complexity of the system, these are likely to persist. The rate of global warming is impossible to predict because it depends on future emissions which can only be approximated. It is also dependent on both positive and negative feedback processes, and unpredictable one-offs like volcanic eruptions. Also uncertain is the degree to which changes in cloud formation, ice coverage, and ocean circulation, and other factors, will impact the rate of climate change2. To a large extent, these uncertainties have been included in climate models and data from past climate changes corroborate these model calculations. And no, the models are not built solely on past data, so it is not circular reasoning; there are factors which are determined simply by physics, not past data. In addition to testing against past data, these climate models have been in operation for some time and have accurately predicted the amount of global warming over the last few decades. They have even predicted the climate results of volcanic eruptions (which have a cooling effect) when the data from those eruptions has been included in the model3.
Another common argument heard from deniers is that “scientists can’t even predict the weather next week, so how can they predict the climate years from now”. This clearly shows either climate change deniers’ ignorance of the difference between weather and climate, or their disingenuousness. Weather is chaotic and often, but not entirely, unpredictable, as anyone who has every received a storm warning will attest. Climate is weather averaged out over time. A reasonable analogy is that while nobody can predict an individual coin toss, you can predict the statistical outcome of a large number of coin tosses3.
As I note above, imposing impossible expectations is another tactic climate change deniers have in common with creationists, and their conclusions are equally worthless.