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[Nederland]

28. The models run cold

When you compare model outputs to observations by using anomalies (how many degrees a given point in time differs from the chosen reference period), the models look ok, tracking 20th century observations fairly well. However, when you look at absolute temperatures the models don't do very well. They often produce absolute temperatures that are 3-4 degrees lower than observations. In other words, if you plotted observed temperatures on top of model predicted temperatures, the temperature line for the model would track the rise and fall of the observed line fairly well, but would sit 3-4 degrees below the observed line.

For purposes of predicting how much temperature will increase due to CO2 rises, comparing anomalies works well. However, because water freezes at a particular absolute temperature, in order to calculate the rate of ice melt you have to look at absolute temperatures, not anomalies. Since the absolute temperatures of the models run cold, you end up under-predicting ice melt.