Climate Data

NOAA 20th-Century Reanalysis, Version 2 and 2c

The Twentieth Century Reanalysis (20CR) provides a comprehensive global atmospheric circulation data set spanning 1850-2014. Its chief motivation is to provide an observational validation data set, with quantified uncertainties, for assessing climate model simulations of the 20th century, with emphasis on the statistics of daily weather. The analyses are generated by assimilating only surface pressures and using monthly SST and sea ice distributions as boundary conditions within a 'deterministic' Ensemble Kalman Filter (EKF). A unique feature of the 20CR is that estimates of uncertainty are derived using a 56 member ensemble. Overall, the quality is approximately that of current three-day NWP forecasts.

20th Century Reanalysis Version v2c uses the same model as version 2 with new sea ice boundary conditions from the COBE-SST2 (Hirahara et al. 2014), new pentad Simple Ocean Data Assimilation with sparse input (SODAsi.2) sea surface temperature fields, and additional observations from ISPD version 3.2.9.

As of 2020, NOAA has released 20CRv3, which covers the period 1806-2015. More information about 20CRv3 will be added to the Climate Data Guide soon.

Key Strengths:

  • Length of record
  • Estimates of uncertainty

Key Limitations:

  • As with all reanalyses, users should take care in interpreting long-term trends - inconsistencies between 20CR and other data have been reported, especially on a regional scale

Years of Record

1850/11 to 2014/12
temporal metadataID:



Sub-daily | Daily | Monthly

Data Time Period Extended?

no, data set not being extended


Spatial Resolution

2°x2°, 28 levels 10 hPA top

Ocean or Land


Missing Data Flag

spatially complete

Data Assimilation Method

Model Resolution used to create reanlaysis

T62 28 levels

Model Vintage (reanalysis)


Input Data

surface and sea level pressure, sea surface temp., sea-ice concentration

Earth system components and main variables

Key Figures

Click the thumbnails to view larger sizes



Climate Data Guide Image: NOAA 20th-Century Reanalysis, Version 2 Air temperature at the lowest model level, sigma.995, from the 20CRV2 ensemble mean. Averaged for 1951-1980. Credit: Climate Data Guide.

Cite this page

National Center for Atmospheric Research Staff (Eds). Last modified 15 Jan 2021. "The Climate Data Guide: NOAA 20th-Century Reanalysis, Version 2 and 2c." Retrieved from

Acknowledgement of any material taken from this page is appreciated. On behalf of experts who have contributed data, advice, and/or figures, please cite their work as well.