Spanning 1871-present at monthly timesteps, HadISST provides the longest gridded sea ice data available for both the Arctic and Antarctic. It is a 1° x 1° spatially infilled data set that is It is intended as a consistent analyses for input into SST analyses or as boundary conditions for models. Version 1.1 is the currently available data set and is the one described here. HadISST combines data from historical ice charts from shipping, expeditions and other activities, passive microwave satellite retrievals (primarily the NASA Goddard NASA Team data set), and NCEP operational ice analyses (also based on NASA Team and NASA Team 2 algorithms). A major update of HadISST is planned and this page will be updated when pertinent information is available. The Climate Data Guide will have a separate page discussing the SST portion of HadISST.