ESA CCI¶

ESA Sea Ice Climate Change Initiative (Sea_Ice_cci) — Sea Ice Concentration and Sea Ice Thickness Climate Data Records

Available

At a glance¶

Note on period: Periods differ by product (whole CEDA collection 1972-12-11 to 2024-04-30). Sea ice concentration: Nimbus-5 ESMR v1.1 1972-12-11 to 1977-05-11; HR-SIC v3 (SSM/I, SSMIS) 1991-01-07 to 2020-12-31; AMSR v2.1 (SICCI-25km, 50km) 2002-06-01 to 2017-05-15 (gap between the end of AMSR-E in 2011-10 and the start of AMSR2 in 2012-07). Sea ice thickness v4.0 Northern Hemisphere monthly grids run from ERS-2 in 1995-10 to CryoSat-2 and Sentinel-3 in 2024-04 (Northern Hemisphere October–April only); the Southern Hemisphere CryoSat-2 monthly grids cover 2010-11 to 2024-04. Drift-aware thickness v1.0 covers the Northern Hemisphere: Envisat 2002-10 to 2012-03 and CryoSat-2 2010-11 to 2020-04. As checked on 2026-10-12, the most recent data are thickness v4.0 for 2024-04.

Overview¶

A set of research climate data records (CDRs) from the ESA Climate Change Initiative (CCI) Sea Ice project. Sea ice concentration comes as SICCI-25km and SICCI-50km (v2.1) from AMSR-E/AMSR2; HR-SIC (v3), a 12.5 km record that sharpens SSM/I and SSMIS data with their near-90 GHz imagery; and Nimbus-5 ESMR (v1.1) from the 1970s. Sea ice thickness comes as trajectory (L2P) and monthly gridded (L3C) data (v4.0) derived from ERS-2, Envisat, CryoSat-2 and Sentinel-3 radar altimeter freeboard, plus daily drift-aware thickness (v1.0) that accounts for ice motion. The concentration records have been developed jointly with EUMETSAT OSI SAF using the same algorithms and formats (OSI-450, OSI-458), and the thickness algorithm, coordinated with C3S, underlies the C3S CDS sea ice thickness product.

What changes with the successor¶

ESA CCI thickness v3.0 → ESA CCI thickness v4.0¶

Transition: 2025-11

The sea ice thickness climate data record moved from v3.0 to v4.0, adding ERS-2 (Northern Hemisphere) and Sentinel-3A/B and extending the record to 2024-04. The v3.0 CEDA records are now marked "This dataset has been superseded", while v4.0 has been published with "Pending" status and as yet no DOI or documentation.

Sources: CEDA — CryoSat-2 Northern Hemisphere L3C v4.0 · CEDA — CryoSat-2 Northern Hemisphere L3C v3.0 (superseded) · CEDA — ERS-2 Northern Hemisphere L3C v4.0 · CEDA — records by Stefan Hendricks (all of v2.0–v4.0) · CCI+ Sea Ice Thickness PUG Issue 3.2 (v3.0)

Available variables¶

Concentration variable names are from the CEDA catalogue (AMSR v2.1, HR-SIC v3) and the HR-SIC PUG; thickness names are from the variable list of the CEDA v4.0 L3C records. Uncertainty variables are named *_standard_error in AMSR v2.1 and ESMR v1.1 but *_standard_uncertainty in HR-SIC v3.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

Sea ice concentration (AMSR v2.1, HR-SIC v3)¶

Sea ice thickness monthly grids (L3C v4.0)¶

Fixed information¶

The full variable list is in the official documentation.

How to get the data¶

• CEDA catalogue — ESA Sea Ice CCI Dataset Collection — HTTP download / OPeNDAP / anonymous FTP (CEDA archive /neodc/esacci/sea_ice/data/) No login needed
  • Public data, available without an account. Example paths: concentration HR-SIC v3 sea_ice_concentration/L4/ssmi_ssmis/12.5km/v3.0/, AMSR v2.1 sea_ice_concentration/L4/amsr/25km(50km)/v2.1, ESMR v1.1 sea_ice_concentration/L3C/esmr/25km/v1.1, thickness sea_ice_thickness/L3C/cryosat2/v4.0/NH(SH). Always check the "Citable as" text on each record.
• CEDA — HR-SIC v3 (SSM/I and SSMIS 12.5 km sea ice concentration) — HTTP / OPeNDAP / FTP No login needed
  • 1991-01-07 to 2020-12-31, both hemispheres. About 21,800 files (78 GB).
• CEDA — CryoSat-2 Northern Hemisphere monthly thickness L3C v4.0 — HTTP / OPeNDAP No login needed
  • 2010-10 to 2024-04, 99 files. The ERS-2, Envisat, Sentinel-3A/B, Southern Hemisphere and L2P records of v4.0 can be found in the CEDA author listing (Stefan Hendricks). The anonymous FTP link on the v4.0 record points to a different path (L2P/envisat/v3.0), so use the HTTP path.
• ESA CCI Sea Ice project page (documents and products) — Web documentation
  • PUGs, ATBDs and validation reports are on the Key Documents page. As of 2026-10-12, no v4.0 thickness documents have been posted.
• C3S Climate Data Store — Sea ice thickness (operational data based on the CCI algorithm) — Web download / CDS API (ECMWF account required)
  • The L3 thickness uses the algorithm developed in the ESA CCI Sea Ice project to join ERS-2, Envisat, CryoSat-2 and Sentinel-3 (October–April). The AMSR products of the concentration dataset (satellite-sea-ice-concentration) also originate from ESA CCI Phase 2 and are updated operationally. For recent years, use these or OSI SAF.

Example code¶

Assumes an HR-SIC v3 daily concentration file and a v4.0 monthly thickness file downloaded from CEDA. The concentration file name follows the pattern given in the PUG; the thickness file is found by the end of its name (…-YYYYMM-fv4p0.nc).

import glob
import xarray as xr

# Sea ice concentration HR-SIC v3 (12.5 km EASE2, Northern Hemisphere)
sic = xr.open_dataset("ESACCI-SEAICE-L4-SICONC-RE_SSMI_12.5kmEASE2-NH-20200315-fv3.0.nc")
c = sic["ice_conc"].squeeze()                      # %
unc = sic["total_standard_uncertainty"].squeeze()  # %, 1 sigma

# Sea ice thickness L3C v4.0 (CryoSat-2, Northern Hemisphere, monthly)
f = sorted(glob.glob("ESACCI-SEAICE-L3C-SITHICK-*CRYOSAT2*-202003-fv4p0.nc"))[0]
sit = xr.open_dataset(f)
ok = sit["quality_flag"] <= 1                      # 0 nominal, 1 intermediate
print(float(sit["sea_ice_thickness"].where(ok).mean()))
print(float(sit["snow_depth"].where(ok).mean()))   # snow depth used in the retrieval (climatology)

Practical tips¶

• The CCI concentration records are research records that end in 2017-05 (AMSR v2.1) and 2020-12 (HR-SIC v3). OSI SAF has taken over the AMSR-based record (SICCI-25km) as OSI-458 (v3.0, "Research to Operations from ESA CCI") and extends it with OSI-438 and OSI-438-a, so if you need a series continued to recent years, use the data on the OSI SAF sea ice concentration page.
• HR-SIC v3 is a pan-sharpened version of OSI-450-a (25 km) using the high-resolution near-90 GHz imagery. Four of its cells align exactly with one OSI-450-a cell, which makes the two easy to compare, but the usual limitations remain: melt ponds are seen as open water and the concentration of thin ice (under 30 cm) is underestimated, and this error is not included in the uncertainty variables (PUG).
• The file attributes describe the v4.0 Southern Hemisphere thickness as an experimental record. Because the algorithm does not properly consider the impact of the complex snow morphology, thickness should be considered biased high in areas with deep snow and during the southern summer months, so do not use it directly for trend analysis.
• CryoSat-2 thickness is available from AWI (v2.6), CCI (v4.0), CPOM and C3S, all from the same source data but with different processing and hence different values. Use one product and one version per analysis and record the version. The differences are summarized on this site's "CryoSat-2" page.
• DOIs differ by product. Concentration (SICCI-25km/50km v2.1, HR-SIC v3, ESMR v1.1) and drift-aware thickness v1.0 have dataset DOIs, but the thickness v3.0 and v4.0 records do not, so cite them with the CEDA record's citation text and URL. Southern Hemisphere drift-aware thickness has only a CEDA record and is not yet published (checked 2026-10-12).

Notices and change history¶

References for your paper¶

Dataset citation¶

Sea ice concentration HR-SIC v3 (SSM/I and SSMIS, 12.5 km) — DOI 10.5285/eade27004395466aaa006135e1b2ad1a

@misc{lavergne2023sicci_hrsic_v3,
  author    = {Lavergne, Thomas and S{\o}rensen, Atle and Tonboe, Rasmus T. and Kreiner, Matilde and Saldo, Roberto and Birkedal, Anton and Baordo, Fabrizio and Aspenes, Trygve and Eastwood, Steinar},
  title     = {{ESA} Sea Ice Climate Change Initiative ({Sea\_Ice\_cci}): High(er) Resolution Sea Ice Concentration Climate Data Record Version 3 ({SSM/I} and {SSMIS})},
  publisher = {NERC EDS Centre for Environmental Data Analysis},
  year      = {2023},
  doi       = {10.5285/eade27004395466aaa006135e1b2ad1a}
}

Sea ice concentration AMSR v2.1, 25 km (SICCI-25km) — DOI 10.5285/f17f146a31b14dfd960cde0874236ee5

@misc{toudalpedersen2017sicci25km_v21,
  author    = {Toudal Pedersen, Leif and Dybkj{\ae}r, Gorm and Eastwood, Steinar and Heygster, Georg and Ivanova, Natalia and Kern, Stefan and Lavergne, Thomas and Saldo, Roberto and Sandven, Stein and S{\o}rensen, Atle and Tonboe, Rasmus T.},
  title     = {{ESA} Sea Ice Climate Change Initiative ({Sea\_Ice\_cci}): Sea Ice Concentration Climate Data Record from the {AMSR-E} and {AMSR-2} instruments at 25km grid spacing, version 2.1},
  publisher = {Centre for Environmental Data Analysis},
  year      = {2017},
  doi       = {10.5285/f17f146a31b14dfd960cde0874236ee5}
}

Sea ice concentration AMSR v2.1, 50 km (SICCI-50km) — DOI 10.5285/5f75fcb0c58740d99b07953797bc041e

@misc{toudalpedersen2017sicci50km_v21,
  author    = {Toudal Pedersen, Leif and Dybkj{\ae}r, Gorm and Eastwood, Steinar and Heygster, Georg and Ivanova, Natalia and Kern, Stefan and Lavergne, Thomas and Saldo, Roberto and Sandven, Stein and S{\o}rensen, Atle and Tonboe, Rasmus T.},
  title     = {{ESA} Sea Ice Climate Change Initiative ({Sea\_Ice\_cci}): Sea Ice Concentration Climate Data Record from the {AMSR-E} and {AMSR-2} instruments at 50km grid spacing, version 2.1},
  publisher = {Centre for Environmental Data Analysis},
  year      = {2017},
  doi       = {10.5285/5f75fcb0c58740d99b07953797bc041e}
}

Sea ice concentration Nimbus-5 ESMR v1.1 (1972–1977) — DOI 10.5285/8978580336864f6d8282656d58771b32

@misc{tonboe2025sicci_esmr_v11,
  author    = {Tonboe, Rasmus T. and Tellefsen, Emil and Kolbe, Wiebke Margitta and Toudal Pedersen, Leif and Lavergne, Thomas and S{\o}rensen, Atle and Saldo, Roberto},
  title     = {{ESA} Sea Ice Climate Change Initiative ({Sea\_Ice\_cci}): {Nimbus-5} {ESMR} Sea Ice Concentration, version 1.1},
  publisher = {NERC EDS Centre for Environmental Data Analysis},
  year      = {2025},
  doi       = {10.5285/8978580336864f6d8282656d58771b32}
}

Sea ice thickness v4.0 — CryoSat-2 Northern Hemisphere monthly L3C (no DOI; cite via the CEDA catalogue URL)

@misc{hendricks2025sicci_sit_cs2_nh_v4,
  author    = {Hendricks, Stefan and Paul, Stephan and Rinne, Eero},
  title     = {{ESA} Sea Ice Climate Change Initiative ({Sea\_Ice\_cci}): Northern hemisphere sea ice thickness from {CryoSat-2} on a monthly grid ({L3C}), v4.0},
  publisher = {NERC EDS Centre for Environmental Data Analysis},
  year      = {2025},
  url       = {https://catalogue.ceda.ac.uk/uuid/887ebbe3aa4345f3bbcbe2dd1834d955}
}

Drift-aware sea ice thickness v1.0 — CryoSat-2 Northern Hemisphere — DOI 10.5285/c7cd8115391340638bdd9adb0fbf28e9

@misc{ricker2025sicci_dasit_cs2_v1,
  author    = {Ricker, Robert and Lavergne, Thomas and Hendricks, Stefan and Paul, Stephan and Down, Emily},
  title     = {{ESA} Sea Ice Climate Change Initiative ({Sea\_Ice\_cci}): Drift-aware sea-ice thickness for the Northern Hemisphere from {CryoSat-2}, v1.0},
  publisher = {NERC EDS Centre for Environmental Data Analysis},
  year      = {2025},
  doi       = {10.5285/c7cd8115391340638bdd9adb0fbf28e9}
}

Reference papers¶

OSI SAF and ESA CCI sea ice concentration CDR version 2 paper (SICCI-25km/50km, OSI-450) — DOI 10.5194/tc-13-49-2019

@article{lavergne2019sic_v2,
  author  = {Lavergne, Thomas and S{\o}rensen, Atle Macdonald and Kern, Stefan and Tonboe, Rasmus and Notz, Dirk and Aaboe, Signe and Bell, Louisa and Dybkj{\ae}r, Gorm and Eastwood, Steinar and Gabarro, Carolina and Heygster, Georg and Killie, Mari Anne and Brandt Kreiner, Matilde and Lavelle, John and Saldo, Roberto and Sandven, Stein and Pedersen, Leif Toudal},
  title   = {Version 2 of the {EUMETSAT} {OSI} {SAF} and {ESA} {CCI} sea-ice concentration climate data records},
  journal = {The Cryosphere},
  volume  = {13},
  number  = {1},
  pages   = {49--78},
  year    = {2019},
  doi     = {10.5194/tc-13-49-2019}
}

CCI sea ice thickness — Envisat–CryoSat-2 linkage paper — DOI 10.5194/tc-12-2437-2018

@article{paul2018envisat_cs2,
  author  = {Paul, Stephan and Hendricks, Stefan and Ricker, Robert and Kern, Stefan and Rinne, Eero},
  title   = {Empirical parametrization of {Envisat} freeboard retrieval of {Arctic} and {Antarctic} sea ice based on {CryoSat-2}: progress in the {ESA} {Climate Change Initiative}},
  journal = {The Cryosphere},
  volume  = {12},
  number  = {7},
  pages   = {2437--2460},
  year    = {2018},
  doi     = {10.5194/tc-12-2437-2018}
}

Drift-aware sea ice thickness method paper — DOI 10.5194/tc-19-3785-2025

@article{ricker2025driftaware,
  author  = {Ricker, Robert and Lavergne, Thomas and Hendricks, Stefan and Paul, Stephan and Down, Emily and Killie, Mari Anne and Bocquet, Marion},
  title   = {Drift-aware sea ice thickness maps from satellite remote sensing},
  journal = {The Cryosphere},
  volume  = {19},
  pages   = {3785--3803},
  year    = {2025},
  doi     = {10.5194/tc-19-3785-2025}
}

Nimbus-5 ESMR sea ice concentration paper (describes v1.0) — DOI 10.5194/essd-16-1247-2024

Acknowledgements¶

Under the ESA CCI Sea Ice terms and conditions, users are required to acknowledge "the ESA Climate Change Initiative and the Sea Ice CCI project" and the data providers in publications, and to cite the relevant CEDA record separately for each product actually used (concentration or thickness, satellite, hemisphere, version). For records without a DOI, such as thickness v4.0, give the CEDA catalogue URL and the download date.

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• ESA CCI Sea Ice Key Documents (PUG, ATBD, validation reports)
• High(er) Resolution Sea Ice Concentration Product User Guide (Issue 3.0)
• Sea Ice Concentration Product User Guide for SICCI-25km/50km (Issue 1.1)
• CCI+ Sea Ice Thickness PUG Issue 3.2 (for v3.0, Zenodo)
• OSI-458 (AMSR sea ice concentration CDR v3.0 taken over by OSI SAF)
• C3S CDS — Sea ice concentration daily gridded data
• CEDA licence — ESA CCI Sea Ice Terms and Conditions