Artists impression of CryoSat-2 in space. Image courtesy of ESA – P. Carril.
An interesting paper was published this week that provides confidence in the accuracy of oceanic Earth Observation data. An European Space Agency (ESA) funded study led by Howarth et al published the paper ‘Global sea-level budget and ocean-mass budget, with a focus on advanced data products and uncertainty characterisation’ in the journal Earth System Science Data.
The team, led by Technische Universität Dresden, used a variety of EO and other data to assess the global mean sea-level rise. They were able to use a monthly time series to demonstrate that satellite measurements were accurate.
High quality EO measurements over the global oceans began in the early 1990’s, and the global mean sea-level has risen by 3 centimetres a decade in this period:
- 38% of this rise was determined to be due to thermal expansion of the warming ocean.
- 57% of the rise was determined to be due to water masses added to the ocean, through:
- melting of glaciers and the two ice sheets in Greenland and Antarctica, which has increased over the period speeding up sea-level rise (47%).
- decrease of water storage on land, mainly due to groundwater depletion caused by human water abstractions (10%).
The team compared the observed sea-level change measured through the change in various components of the overall sea-level budget, with measurements form EO satellites. The observed component measurements between 1993 and 2016 showed an increase of 2.90 mm per year, whilst the EO satellites recorded a 3.05 mm rise per year, giving confidence in the accuracy of EO data.
Earth Observation Satellite Data Used
The team used data from ESA’s Climate Change Initiative (CCI), which provides free-to-access datasets for a number of Essential Climate Variables (ECV). It is an initiative we know well as Pixalytics are part of the team responsible for the production of the Ocean Colour CCI datasets.
Specifically, the study used the Sea Level CCI project that combines altimetry data from the TOPEX/Poseidon, Jason-1 and Jason-2, GFO (Geosat Follow-On), ERS-1 and ERS-2 (European Remote Sensing), Envisat, CryoSat-2, and SARAL (Satellite with ARgos and ALtiKa) missions. In addition, a variety of measurements from the Gravity Recovery and Climate Experiment (GRACE) satellite were also used within the methodology. The satellite data was supported by analysis of the Argo drifter data, global glacier model and a global hydrological model. The time-series data set is available here for download.
The results of the team are consistent with other studies, and it formed part of the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) that we reported on last year.
It is a positive example of the accuracy of satellite observations, although the report acknowledges that there is still further work to do. There is a need to bring the satellite measurements together with the physical processes to further understand what is happening in the oceans, which is a critical element of climate change and the impact of sea-level rise.
