Past climateClimate models can be used to create reconstructions and studies of what the climate was like in the past. To make the models as reliable as possible, data assimilation is used, a method for transferring observations of various variables into mathematical models. We create reanalyses – reconstructions – of past climatic conditions. Ongoing reanalyses will be able to provide information about the climate 1,000 years back in time. In addition to data from satellites and recent direct measurements, data from core samples, tree rings, pollen, and plankton deposits are used. Such retrospectives in time help us to understand natural climate variations and to find other influencing factors. Reanalyses can also be used to improve climate models, which in turn will improve the quality of climate projections. For more information, contact research leader François Counillon. Software For access to NorCPM, a tool for producing climate forecasts and reanalyses, go to the NorCPM-info page for information. All the code to run the system is available on GitHub. Access is private, so request an account to gain access.