Actual and hindcast 50 year change in Arctic temperature (1957-2006)

The 50 year temperature record of temperature in the Arctic and the Northern Hemisphere (to the left) show clear mean temperature changes. The information about future change in the Arctic is based on results from 24 different computer models of the global climate system. These simulate the dynamic behavior of the atmosphere and the oceans. To test how well a model simulates reality, the model is run for past periods for which we already know the outcome - this is known as hindcasting (see right-hand globe). Models that produce very different results from the majority of models, or very unlikely results like sea ice in the tropics, are excluded from this assessment.