This sentiment is not correct - causal explanations do matter. The statistical evidence for global warming is not particularly strong, as temperature data is very noisy. If we didn't have a causal explanation there would not be a scientific consensus behind climate change. That adding greenhouse gases to the atmosphere changes the climate is more like gravity - we have clear physics on why things fall when you drop them, and if we somehow were adding mass to the center of the earth we know what effect this would have.

More generally you are correct, we don't know exactly how much the earth will warm or if there are complicated feedback mechanisms in place that could cause this warming to speed up or reverse course. We can't even reliably say that next year will be hotter than this year (actually it probably will be cooler because this year has been unusually hot).