This dataset contains a landfast ice climatology calculated from MODIS imagery. For a complete description of the methods, please see Cooley and Ryan (forthcoming). This dataset contains a shapefile "landfast_ice_edge_2000_2022.shp" of maximum ice edge positions derived from MODIS imagery. The 'time period' column refers to the 30-day period over which the edge position was calculated, specifically 1: March 1st to April 1st, 2: March 15th to April 15th and 3: April 1st to May 1st. For years with multiple lines and/or multiple time periods present in the dataset, we retain the maximum position in our analysis; in other words, we calculate the ice edge position based on the furthest line from the coast. This dataset also contains time series of ice edge position (distance to the ice edge from the coastline, in km) and breakup timing. The ice edge position is calculated as the maximum ice edge distance from coastline using the ice edge shapefile described above. The breakup date is defined as the day when 75% of the area contained within the maximum ice edge position for that year reaches open water. This is corrected for cloud cover by assigning the actual breakup date as the midpoint between the first day when the ice was open water and the previous cloud-free observation. This uncertainty (in days) is recorded as "breakup_uncertainty". Any usage of this data should cite Cooley and Ryan (forthcoming). For any questions about the dataset, please reach out to Sarah Cooley at scooley2@uoregon.edu