% Berkeley Earth Surface Temperature % % README file for Land and Ocean Gridded Data % % This description was written in 2026 to replace the original file, which % is no longer available. It is based on the README for the land-only % gridded data, the files themselves, and the code that wrote them. % % This file describes the format used by the Berkeley Earth Surface % Temperature project for the gridded land and ocean temperature fields. % These fields contain reconstructed monthly temperature anomaly values % formed by combining the Berkeley Earth land-surface air temperature field % with a reinterpolated version of the HadSST4 ocean temperature field. % The current citation for this dataset is: % % Rohde, R. A. and Hausfather, Z.: The Berkeley Earth Land/Ocean Temperature % Record, Earth Syst. Sci. Data, 12, 3469-3479, % https://doi.org/10.5194/essd-12-3469-2020, 2020. % % The dataset differs slightly from the dataset as described in the citation % as HadSST3 has been replaced with the newer HadSST4, and associated % interpolation parameters have been refit accordingly. % % The data are released under the Creative Commons BY-NC 4.0 International % license, https://creativecommons.org/licenses/by-nc/4.0/ % % These files were last updated in January 2025, with data from January 1850 % through December 2024. The high-resolution Berkeley Earth data set is % described at https://berkeleyearth.org/data/ % % All gridded data is provided in the NetCDF format (version 4). Tools for % reading NetCDF are available in most programming languages, including % Python, Matlab, R and C++. % % Sea Ice % % Two versions of the field are provided. They differ in how they treat % locations with sea ice. For most of the ocean, sea surface temperatures % are similar to near-surface air temperatures; however, air temperatures % above sea ice can differ substantially from the water below the sea ice. % % Land_and_Ocean_.nc Temperature anomalies in the presence % of sea ice are extrapolated from % land-surface air temperature % anomalies. % % Land_and_Ocean_Alternate_.nc Temperature anomalies in the presence % of sea ice are extrapolated from sea % surface water temperature anomalies, % usually collected from open water on % the periphery of the sea ice. % % The air temperature version shows larger changes in the recent period, in % part because water temperature changes are limited by the freezing point of % ocean water. We believe that the use of air temperatures above sea ice % provides a more natural means of describing changes in Earth's surface % temperature. The percent coverage of sea ice was taken from the HadISST v2 % data set and varies by month and location. % % File Naming Convention % % indicates the type of gridded data provided: % % EqualArea The 15,984 element equal area grid which is the format % commonly used by the Berkeley Earth project to represent the % globe. % % LatLong1 The field resampled onto a 1 degree by 1 degree % latitude-longitude grid covering the Earth. This format is % likely to be more useful for many applications. % % File Contents % % Each file holds the following variables. Dimensions are listed in the % order NetCDF stores them; Matlab reports them in reverse order. % % EqualArea LatLong1 % longitude (map_points) (longitude) % latitude (map_points) (latitude) % time (time) (time) % land_mask (map_points) (latitude, longitude) % temperature (time, map_points) (time, latitude, longitude) % climatology (month_number, map_points) (month_number, latitude, longitude) % % latitude, longitude: The centers of the grid cells, in degrees. Positive % values are north of the equator and east of Greenwich. For EqualArea % they list every cell; for LatLong1 they list the centers of a single % column and a single row. % % time: The time of each field, as a decimal year at the middle of the month. % For example, 1981.125 indicates February 1981. % % land_mask: For each grid cell, the fraction of the cell which is land, as % opposed to ocean or other large water bodies. % % temperature: The surface temperature anomaly, in degrees C, relative to the % January 1951 to December 1980 average for that cell and calendar month. % Over land it is air temperature; over open ocean it is derived from sea % surface temperature; over sea ice it is as described above. Missing % values are reported as NaN. A value is reported as missing if the % coverage diagnostic indicates that the locally available data provides % less than a 20% constraint on the anomaly. % % climatology: For each grid cell, an estimate of the true surface % temperature for each calendar month during the period January 1951 to % December 1980, in degrees C. month_number has length 12, January through % December. Adding the climatology of the calendar month to an anomaly % gives an estimate of the absolute temperature. % % The global comment attribute of the LatLong1 files repeats the text of the % EqualArea files, which describes the native equal-area format. % % The gridded data files do not contain uncertainty information.