By Elisa Jiménez Alonso
A study released earlier this year shows that sea level rise is already happening, and it is accelerating.
Gathering and evaluating satellite data from different missions, like Jason-3 and TOPEX/Poseidon, a team of researchers led by University of Colorado-Boulder professor Steve Nerem found that in the last 25 years sea levels had risen a total of 7 centimetres. However, the rate at which this happened was not constant but has increased.
Using data from the Gravity Recovery and Climate Experiment, also called GRACE, the scientists determined that the acceleration is caused by global warming. More than half of the observed sea level rise is due to thermal expansion, meaning that as ocean water gets warmer it expands and its level rises. The rest can be attributed to melting ice from Greenland’s and Antarctica’s ice sheets.
The observed acceleration has the potential to “double the total sea level rise by 2100 as compared to projections that assume a constant rate – to more than 60 centimetres instead of about 30,” according to Nerem.
The projections from this new study also align with those from the climate models used by the Intergovernmental Panel on Climate Change (IPCC). Using Earth observation data, the scientists have observed evidence that validates those model projections providing a “data-driven assessment of sea level change that does not depend on the climate models.” The IPCC models show sea level rise between 52 and 98 centimetres by the end of this century under a business-as-usual scenario in which current emissions are not reduced.
For coastal cities such projections are a worrying signal as they could cause unprecedented problems and flooding during high tides and storm surges. Even though the number might not sound like much, the records set in Boston Harbor during this year’s ‘bomb cyclone’ or the regular inundations in Miami during king tides are occurring with the seven-centimetre sea level rise from the past century.
S. Nerem, B. D. Beckley, J. T. Fasullo, B. D. Hamlington, D. Masters, G. T. Mitchum (2018). Climate-change–driven accelerated sea-level rise. Proceedings of the National Academy of Sciences Feb 2018, 201717312; DOI: 10.1073/pnas.1717312115