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News Flash 04/12/2019

Mean sea level: a key indicator of global warming established in Toulouse

Understanding climate mechanisms means first of all understanding the ocean. But how can we learn more about this immense maritime territory? Over the last 30 years, observation systems for the ocean have made giant leaps. The development of satellites for space oceanography and collection of environmental data has been the driving force behind this revolution. From the start, CLS was a pioneer in the field, and receives, processes, and qualifies these satellite data for the entire international community. As world leader in altimetry and the exclusive supplier of the ARGOS system for location and collection of environmental data, CLS works daily with experts in climatology. Today, they provide us with their perspective and give us an update on the planet’s health.

Anny Cazenave is a member of the Academy of Science and of the Intergovernmental Panel on Climate Change. She is a renowned researcher on climate change and routinely uses CLS’s mean sea level indicator. She tells us just how important it is and emphasises the leading international position of CLS in establishing this key indicator of global warming.


Why is it important to determine mean sea level?

Mean sea level is one of the best indicators of global warming. Certainly much better than mean global temperatures. Today, because of greenhouse gas emissions generated by human activities,
our planet has an energy disequilibrium. It is accumulating heat and 93% of this excess heat is stored in the oceans. The remaining heat is causing the ice caps to melt and is heating the atmosphere. Sea level is related to ocean warming and ice cap melting, and are therefore a key indicator of global warming. This is because heat that accumulates in the oceans dilates the water, resulting in higher sea level. Melting mountain glaciers and the loss of ice mass in Greenland and Antarctica are another cause of the current rise in sea level.


How do you use this indicator?

At LEGOS, we are trying to understand the regional and global causes of changes in sea level. Our research has shown that the mean overall rise in sea level over the past 20 years is caused for about 35% by ocean warming, 45% by melting of continental ice, and 10% by pumping water from underground sources, since this water ultimately ends up in the ocean. The remaining 10% is not accounted for at this time, but is most probably related to uncertainties in measurements. To establish a very clear picture, we need data that are as accurate as possible. CLS has been working extensively these past few years on precise calculations of sea levelsbased on space altimetry data from several satellites. Today, CLS provides us with highly accurate “sea level” products The “sea level” indicator calculated by CLS is increasingly reliable and more and more accurate. It is no doubt one of the best products available today.


Why is this indicator crucial for managing the climate?

Mean sea level is rising, as we said. It is a key indicator of current global warming. The time-series of sea level measurements taken by CLS are also used to validate the climate models developed to simulate future changes.