Europe ERA5 Air and Sea Temperature Tracker

Domain and source data

Dataset

ECMWF Reanalysis v5 (ERA5)

Spatial domain

30°–72° N, 25° W–40° E

CDS grid

0.25° × 0.25°; 44,109 grid points

Data coverage

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The tracker uses ERA5 hourly data on single levels from the Copernicus Climate Change Service (C3S) Climate Data Store. ERA5 is a global atmospheric reanalysis produced with the ECMWF Integrated Forecasting System (IFS) and four-dimensional variational data assimilation (4D-Var). Observations from many observing systems are combined with the numerical model to reconstruct a physically consistent atmospheric state through time.

2 m air temperature. This is the estimated air temperature two metres above the model surface and is available across both land and sea. In the IFS it is a diagnostic screen-level quantity rather than the temperature of a model level: it is derived from the temperature at the lowest atmospheric model level and the underlying surface skin temperature using boundary-layer stability information. The hourly 2 m temperature distributed through the ERA5 Climate Data Store is an analysed parameter, so it is consistent with the observation-constrained atmospheric state produced by the reanalysis.

Sea surface temperature (SST). ERA5 SST is a prescribed foundation sea surface temperature rather than a prognostic temperature generated by the atmospheric model. Before September 2007 it is based on HadISST2; from September 2007 onward it is based on the Met Office OSTIA analysis. The ERA5 SST represents a foundation temperature without a resolved daytime solar-warming cycle. Although the field is available at hourly timestamps, its SST content is updated once per day.

ERA5 values are reanalysis estimates rather than direct weather-station observations. Apparent local records or other extremes that are important for a specific application should therefore be checked against observations and, where appropriate, other climate datasets.

Data availability. Recent data are initially provided by C3S as preliminary ERA5T and are typically available about five days behind real time, with no guaranteed release time. This tracker updates daily and normally operates about six days behind real time. C3S subsequently replaces ERA5T with final ERA5 data, normally about two months later, so values from the most recent months should be regarded as preliminary.

Data citation: Hersbach H, Bell B, Berrisford P, et al. ERA5 hourly data on single levels from 1940 to present. Copernicus Climate Change Service Climate Data Store. doi:10.24381/cds.adbb2d47. For broader background on reanalysis, see Advancing Reanalysis.

Copernicus attribution and disclaimer. Contains modified Copernicus Climate Change Service information 2026. The European Commission and ECMWF are not responsible for uses made of the Copernicus information or data presented on this page.

How the tracker is calculated

Daily temperature. Daily means are defined over 00:00–23:00 UTC. The historical archive was calculated from the 24 hourly ERA5 values. Operational updates use the C3S ERA5 daily-statistics service configured for a daily mean in UTC with 1-hourly sampling, applying the same daily averaging window. For 2 m air temperature, a complete set of hourly values is required; SST is retained only for complete valid daily values. ERA5 SST is available at hourly timestamps, but its ocean SST content is updated once per day.

Map smoothing. The colour raster uses bilinear interpolation between neighbouring 0.25° grid cells to provide a smoother visual representation of the ERA5 field. For SST, interpolation is additionally weighted by fractional ocean coverage from the ERA5 land–sea mask; pixels with less than 50% interpolated ocean fraction are left transparent. Interpolation is strictly a display operation. Clicking the map snaps to the nearest ERA5 grid point, and all reported temperatures, line plots, anomalies, rankings, and other calculations use the original daily grid-point values rather than interpolated map pixels.

Historical comparison. This is calculated separately for every calendar date. Across the selected historical years, the chart shows the median and the 10th–90th percentile range after applying the chosen raw, 7-day, or 15-day trailing mean. In temperature mode, the 1991–2020 WMO standard climatological mean is also shown as a separate line. A trailing mean includes the plotted date and the preceding 6 or 14 days.

Daily mean anomaly. This is the daily mean temperature minus the mean for the same calendar date during the selected 30-year baseline. The default is 1991–2020, the current WMO standard climatological reference period; the slider also allows any complete 30-year window from 1940–1969 through 1991–2020. The zero line therefore represents the selected baseline climatology. Leap day has its own calendar position and is calculated from leap years only. The 7- and 15-day anomaly curves are trailing means of these daily mean anomalies.

Year-to-date mean anomaly. This is the mean of all available daily anomalies from 1 January through the plotted date. Rankings compare the latest year with years having at least 90% valid coverage through the same calendar date.

Annual mean anomaly. This is the mean of the daily anomalies over a complete calendar year. The incomplete latest year is shown separately as a provisional year-to-date value so that it is not mistaken for a completed annual mean.

Full-domain area-weighted mean. When the full-domain time series is shown, each 0.25° latitude–longitude grid cell is weighted in proportion to its physical area. For 2 m air temperature, all valid land and sea cells within the complete 30–72° N, 25° W–40° E domain are included, with weights proportional to the cosine of latitude. These values are therefore not equivalent to a land-only European mean reported by C3S or other climate-monitoring products. The full-domain mean is calculated from the original ERA5 grid values before any map interpolation. For SST, the same latitude weighting is combined with the fractional ocean area from the ERA5 land–sea mask so that coastal cells contribute only their ocean fraction. When no grid point has been selected, the line chart uses these daily full-domain area-weighted means; historical distributions, anomalies, year-to-date rankings, and annual anomalies are then calculated from that series.