The latest global products including uncertainties are provided via the CCI Open Data Portal
How is Sea Level measured
Past variations can be reconstructed from several indicators, but the very first measurements of sea level were made by monitoring tides in the 18th century. Although we now have a relatively dense network of tide gauges, only 20 stations (mostly along the coasts of Europe and North America) collected data throughout the 20th century. On the basis of their measurements, sea level is estimated to have risen by 10 to 20 centimetres since 1900.
Today, satellite altimetry, autonomous floats (Argo floats since 2005) and gravimetric data (GRACE satellite) enable the measurement of mean sea level variations, or some of their components. Ocean models are also used to understand and quantify those phenomena.
With the satellite altimetry missions, the global mean sea level (GMSL) has been calculated on a continual basis since January 1993. 'Verification' phases, during which the satellites follow each other in close succession (Topex/Poseidon-Jason-1, Jason-1-Jason-2, Jason-2-Jason-3, and then Jason-3-Sentinel-6), help to link up these different missions by precisely determining any bias between them. Envisat, ERS-1 and ERS-2 are also used, after being adjusted on these reference missions, in order to compute Mean Sea Level at high latitudes (higher than 66°N and S), and also to improve spatial resolution by combining all these missions together. In addition, permanent monitoring of quality during the missions and studies of the necessary corrections of altimetry data regularly add to our understanding and knowledge.
Why Sea Level varies
There are several possible components which may take their part in the mean rise in sea level: an increase in the temperature of the water, which dilates as it warms, the thawing of mountain glaciers and polar ice caps in Greeland and Antarctica, as well as melting permafrost. Changes to the amount of rainfall and evaporation also play a part, as well as runoff and inland water reserves, mainly owing to human activity such as dam construction and irrigation.
Different altimeter sea level products have been produced and distributed within the Sea Level Climate Change Initiative (SL_CCI) project. Access to the ECV Products and further details are provided via the CCI Open Data Portal. All available SL_cci datasets are presented below and the collection can be found on this page. The users are invited to contact the team for any question on the products: info-sealevel@esa-sealevel-CCI.org.
The different products available are listed below:
The regional XTRACK/ALES altimeter along-track multi-mission high frequency sea level anomalies
- V1.0 consists of SLA datasets covering the period 2002-2016 in the Western Africa, Mediterranean Sea and North East Atlantic Ocean. DOI: 10.5270/esa-sl_cci-xtrack_ales_sla-200201_201610-v1.0-201910.
- V1.1 SLA are the extension of v1.0 in time (up to 2018) and cover three additional regions: North Indian Ocean, South-East Asia and Australia. DOI: 10.5270/esa-sl_cci-xtrack_ales_sla-200206_201805-v1.1-202005.
- V1.1 SLA have been used to derive a new network of altimetry-based virtual stations of sea level in the world coastal zones: a database of monthly-averaged post-processed SLA and associated trends estimated along the tracks at 429 selected coastal sites from 2002 to 2018. This product is dedicated to the analysis of coastal sea level trends (DOI: https://doi.org/10.17882/74354).
- The updated V2.1 network of altimetry-based sea level virtual stations (756 coastal sites) has been produced , including a temporal extension until Dec. 2019 and a spatial extension around the american continent.
- A reprocessed improved v2.2 network of altimetry-based sea level virtual stations (756 coastal sites) is now available for the users (DOI: https://doi.org/10.17882/74354).
The global sea level ECV product is a multi-satellite merged product that consists in a database of different elements that can be referenced with the following DOI: 10.5270/esa-sea_level_cci-1993_2015-v_2.0-201612. The v2.0 dataset covers the period Jan. 1993 to Dec. 2015 and includes:
- Time series of gridded Sea Level Anomalies (SLA):
The SLA grids are calculated after merging all the altimetry mission measurements together into monthly grids with a spatial resolution of 1/4 of degree.
- Oceanic indicators:
Static files over the whole altimetry operating period describing the evolution of the SLA grids just previously mentioned
- Global Mean Sea Level temporal evolution. DOI: 10.5270/esa-sea_level_cci-IND_MSL_MERGED-1993_2015-v_2.0-201612
- Regional Mean Sea Level trends. DOI: 10.5270/esa-sea_level_cci-IND_MSLTR_MERGED-1993_2015-v_2.0-201612
- Maps of the amplitude and phase of the annual cycle. DOI: 10.5270/esa-sea_level_cci-IND_MSLAMPH_MERGED-1993_2015-v_2.0-201612
- Fundamental Climate Data Record (FCDR):
The FCDRs are the along-track SLA derived from each altimeter mission, available at 1Hz resolution corresponding to a ground distance of about 7 km. The files include a quality control and all altimeter standards applied in the SLA calculation. Global and regional inter missions biases are also included.
- Errors of oceanic indicators:
The Climate Assessment Report presents the work dedicated to the quality assessment of the products by the Climate Research Group and the Comprehensive Error Characterization Report describes the altimetry error budget (different sources of altimetry errors, global MSL confidence envelop, etc).
- WARNING 1: An instrumental drift has been detected in the TOPEX-A altimeter measurements during 1993-1998 and the users are informed that the SL_cci v2.0 global sea level maps (and the corresponding FCDRs as well as the derived indicators) have not been corrected for this drift. Depending on the application, the users are invited to correct the time series for this drift (see WCRP Global Sea Level Budget Group, 2018).
- WARNING 2: Following the ESA CCI efforts made to produce the sea level record, the operational production of the climate-oriented sea level product has now been taken over by the Copernicus Climate Change Service (C3S, https://climate.copernicus.eu/ ) through the climate data store (dataset "Sea level daily gridded data..."). Data after 2015 are available and in order to be consistent, you are invited to download the total C3S timeseries from 1993 onwards.
The altimeter SL_cci sea level anomalies (v2.0 global ECV product) have been produced with the use of the Dynamic Atmospheric Correction (DAC) forced by the ERA-Interim reanalysis. The associated 6-hourly global grids are available for the users. Contact info-sealevel@esa-sealevel-CCI.org for access to this dataset. (not available in the Open Data Portal, ODP)
The Product User Guides (PUG) related to the global sea level ECV product and the XTRACK/ALES regional coastal product can be found in the “Key Documents” section. The description of the different products and their validation can be found in the technical documents listed in this section, in the references listed below and in peer-reviewed articles of the SL_cci team listed here.
Terms and conditions & Acknowledgement
The Sea Level CCI datasets may be used by any user for any purpose ("CC-BY" licence).
Users of the Sea Level CCI datasets are invited to cite the relevant DOI (as mentioned in the above table) and cite the relevant articles (see table below)
- The Sea Level ECV v2.0
Legeais, J.-F., Ablain, M., Zawadzki, L., Zuo, H., Johannessen, J. A., Scharffenberg, M. G., Fenoglio-Marc, L., Fernandes, M. J., Andersen, O. B., Rudenko, S., Cipollini, P., Quartly, G. D., Passaro, M., Cazenave, A., and Benveniste, J.: An improved and homogeneous altimeter sea level record from the ESA Climate Change Initiative, Earth Syst. Sci. Data, 10, 281-301, https://doi.org/10.5194/essd-10-281-2018, 2018.
Quartly, G. D., Legeais, J.-F., Ablain, M., Zawadzki, L., Fernandes, M. J., Rudenko, S., Carrère, L., García, P. N., Cipollini, P., Andersen, O. B., Poisson, J.-C., Mbajon Njiche, S., Cazenave, A., and Benveniste, J.: A new phase in the production of quality-controlled sea level data, Earth Syst. Sci. Data, 9, 557-572, https://doi.org/10.5194/essd-9-557-2017, 2017.
- The regional XTRACK-ALES coastal sea level product
Birol F., F. Léger, M. Passaro, A. Cazenave, F. Niño, F. Callafat, A. Shaw, J.-F. Legeais, Y. Gouzenes, C. Schwatke and J. Benveniste. The X-TRACK/ALES multi-mission processing system: new advances in altimetry towards the coast, Advances in Space Research, https://doi.org/10.1016/j.asr.2021.01.049, 2021.
Passaro, M., A., N., Zulfikar, 2018. Improving the precision of sea level data from satellite altimetry with high-frequency and regional sea state bias corrections, Remote Sensing of Environment, 218, 245-254, https://doi.org/10.1016/j.rse.2018.09.007.
- The network of altimetry-based virtual stations (monthly SLA and trends at selected sites):
Cazenave A., Gouzenes Y., Birol F., Leger F., Passaro M., M. Calafat F., Shaw A., Nino F., Legeais J.-F., Oelsmann J., Restano M. and Benveniste J., Sea level along the world’s coastlines can be measured by a network of virtual altimetry stations. Commun Earth Environ 3, 117 (2022). https://doi.org/10.1038/s43247-022-00448-z
Benveniste and the Climate Change Initiative Coastal Sea Level Team., Coastal sea level anomalies and associated trends from Jason satellite altimetry over 2002–2018. Sci Data 7, 357 (2020). https://doi.org/10.1038/s41597-020-00694-w