One of the favorite criticisms harped on by deniers is that global temperature isn’t rising as fast as computer models have predicted. So far, comparisons have shown that observed temperature is on the low end, even skirting the significantly low end, of model results. They generally use this to imply, or say outright, that not only are models “wrong wrong wrong” but the whole of climate science is “wrong wrong wrong.”
Of course it might be a valid criticism of the models, but not of global warming theory which most decidedly does not depend on complex computer models. The models are just our best way of forecasting what the future will bring; they aren’t necessary to understand, or confirm by many observations (not just temperature data), the physics behind man-made climate change.