Climate prediction is similar to numerical weather prediction, but the forecasts are for longer periods. Special numerical models are used to alter trace atmospheric gases (carbon dioxide and methane, for example), sea ice and glacier cover, changes in incoming solar radiation, and a host of other parameters. The following climate prediction datasets are avilable. GM2 Global Coupled Climate Models consist of two climate models, which were designed to model the changes in climate over the past century and into the 21st century. The climate forecast system is a medium to long range numerical weather predicition and climate model run by the US National Centers for Environmental Prediction (NCEP) to bridge weather and climate timescales.