Hansen and some of the other leading climatologists disagree with the current models. Hansen points out that the models consistently have been too low on ice melt rates even just a few years after the model date. Hansen believes that there is a positive feedback loop(s) that is not accounted for in current models and which may result in catastrophic melt rates within 50 years. His argument is that the models have consistently been too conservative and that melt rates are reaching, in just a few years, levels not predicted for decades. Since this higher-than-predicted melt rate is observable fact, the models must be wrong and the only question becomes exactly how fast can these ice sheets melt?