Well yeah, that's why a model is a hypothesis. That doesn't mean that the hypothesis can't be proven (or disproven). Actually, that's one of the main criticisms I have about climate models; I actually agree that climate change is possible/happening, but the timelines they give are flat out not provable based on the accuracy of their models. Even if they can prove that the earth is warming due to CO2, they can't actually give any concrete predictions about what that overall effect will be. There are a whole bunch of non-linear and chaotic relationships that are hard to predict over time, and yet they assert they know what will happen. Global warming might actually increase arable land and might be a boon to the shitholes of the world.