Page Overview & Data Sources

• This page provides time series and map visualizations of daily mean surface air temperature (2-meter height) estimates from the ECMWF Reanalysis version 5 (ERA5) for the period January 1940 to present (see ERA5 attribution below). ERA5 is a state-of-the-art numerical climate/weather modeling framework that ingests surface, radiosonde, and satellite observations to estimate the state of the atmosphere through time. The visualizations on this page enable users to explore weather-driven temperature changes within specific years, while also having several decades of daily data for broader climate context. Users are encouraged to learn more about reanalysis — approach, strengths, limitations, and product comparisons — from the NCAR Climate Data Guide. Additional information about reanalysis can be found at Advancing Reanalysis.
  
  Please Note: This content is intended for general analysis only. Any apparent record high or low daily temperatures estimated by ERA5 should be considered with caution and validated against weather station observations and other climate data products. Regarding high global mean temperatures in July 2023, Copernicus C3S and the World Meteorological Organization issued this statement. The NOAA National Centers for Environmental Information (NCEI) made a similar assessment.
  
  A comparison of annual temperature anomaly time series for ERA5 and other datasets can be found here. Additional information about ERA5, including strengths and limitations, is available from the NCAR Climate Data Guide. Users are also encouraged to check out NOAA NCEI's Climate at a Glance for monthly, seasonal, and annual surface temperature anomaly estimates 1850 to present.


• The time series chart displays area-weighted mean temperature estimates for the following domains:
  
  World (90°S–90°N, 0–360°E) Northern Hemisphere (0–90°N, 0–360°E) Southern Hemisphere (0–90°S, 0–360°E) Arctic (66.5–90°N, 0–360°E) Antarctic (66.5–90°S, 0–360°E) Tropics (23.5°S–23.5°N, 0–360°E)
  The ERA5 output files downloaded from Copernicus C3S have a horizontal grid resolution of 0.25° x 0.25° (about 31km x 31km at 45°N). Each daily temperature on the chart represents an average across all model gridcells within the defined latitude/longitude bounds for the selected domain. The means are area-weighted to account for the convergence of longitude lines at the poles.
  
  Individual time series can be hidden or displayed by clicking on a specific year below the chart. Hide All and Show All buttons are found at the chart lower right. Temperature anomalies in the chart tooltip (appears when the cursor is hovered over a data point) are in reference to 1979–2000 climatology for each specific day of the year. For reference, the times series for the 1979–2000 climatology is plotted on the chart in addition to the more commonly used 30-year 1981–2010 and 1991–2020 climate normals.
  
  The daily mean temperature map below the chart can be updated by clicking a point on one of the time series. The measurement displayed on the map variable can be switched between temperature and temperature anomaly by clicking the toggle botton at the map top-left.


• The temperature estimates on this page are calculated from eight hourly timeslices (00, 03, 06, 09, 12, 15, 18, 2100 UTC) for each day in the ERA5 dataset. The chart and maps update daily by about 1800 UTC with a lag time of 6–8 days from the current date.


• NCAR Command Language is used for data processing and map generation. The interactive time series chart is made with HighCharts.

ERA5 Attribution

• Data Source: Copernicus Climate Change Service (C3S) (2023): ERA5 hourly data on single levels from 1940 to present. Copernicus Climate Change Service (C3S) Climate Data Store (CDS). 10.24381/cds.adbb2d47 (Accessed daily 2023).
  
  Data Citation: Hersbach, H., Bell, B., Berrisford, P., Biavati, G., Horányi, A., Muñoz Sabater, J., Nicolas, J., Peubey, C., Radu, R., Rozum, I., Schepers, D., Simmons, A., Soci, C., Dee, D., Thépaut, J-N. (2018): ERA5 hourly data on single levels from 1940 to present. Copernicus Climate Change Service (C3S) Climate Data Store (CDS). 10.24381/cds.adbb2d47 (Accessed daily 2023).
  
  Disclaimer: Contains modified Copernicus Climate Change Service information 2023. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.

Last updated 10 December 2023