Anny Cazenave is a scientific reference in France. In 2004 he conquered a seat in the Academy of Sciences of the neighboring country, and in 2008, in the United States. In the North American country the American Geophysical Union awarded him four years later its maximum decoration, the William Bowie Medal. And all because this 75-year-old Frenchwoman born in Draveil, a town on the Parisian outskirts crossed by the Seine, has spent the last quarter of a century measuring the rise in sea level from space thanks to Franco-American cooperation. Cazenave, PhD in Geophysics from the University of Toulouse, is scientific emeritus of the Laboratory of Studies in Geophysics and Space Oceanography (LEGOS). In 2013 she joined the International Institute of Space Science, based in Bern (Switzerland), where she is currently director of Earth Sciences.
Respond to EL PAÍS by questionnaire, after having received the Frontiers of Knowledge award from the BBVA Foundation together with his colleagues John Alexander Church and Jonathan Gregory for being pioneers in integrating the observations of the sea on the surface with the data of the satellites, "that for the first time they cover the entire oceanic domain. "
Question. How is sea level rise measured from space?
Answer. Altimetry satellites are used [lanzan un pulso de radar hasta la superficie y regresa] They measure it with a very high precision and they cover the entire oceanic domain in a few days. When they finish, they return to the same regions on a regular basis, which allows them to follow the evolution over time.
Can they detect garbage with these satellites?
We must be able to see the plastic waste that accumulates in certain areas of the ocean with the image satellites. But not with lThe altimetry satellites are not good for that.
And how much does the sea level rise?
On average, the climb is 3 millimeters per year, but a clear acceleration is observed. Also, it does not rise evenly. In some regions, it does it three times faster than the average. During the last 25 years, when the first satellite measurements began, the sea level has grown an average of 8 centimeters. However, in the western region of the tropical Pacific Ocean, the rise reaches 25 centimeters.
Geodesy studies the shape and dimensions of the Earth. In addition to measuring the growth of the sea, what are its applications?
It has many and in a large number of areas: geolocation [GPS] or movement of tectonic plates, for example. It is also used to identify deformations in the earth's crust in regions with seismic activity. In addition, it serves to measure the water reserves in the continents and even the variations in the gravity of the Earth.
Attributes the rise of the sea to the thermal expansion of the oceans and glaciers, has this changed the shape of the planet?
Undoubtedly, this rise has changed the shape of the Earth, but the transformation is very small in the scale of the planet.
What did you do with the observations of the TOPEX / Poseidon satellite to quantify changes in sea level?
Measurement data collected by this satellite and its successors Jason-1, Jason-2, Jason-3 were used in my team to track this rise in sea level. Also to study the causes, that is, the warming of the ocean and the melting of the poles.
Why were they an innovation?
Because for the first time very accurate data were obtained from the entire oceanic domain.
What did we not know before the age of the satellites of the changes in the sea that we know now?
Before we only had limited information that came from the tide gauges that were installed in the ports. So we did not know how much the sea rose in the deepest regions far from the coast.
What do we still not know about this phenomenon?
When the altimetry satellites approach the coast, the measures they obtain degrade [por los rebotes de la señal en las zonas terrestres]. That is why it is not yet known with real precision the sea level rise in these regions. The objective now is to use new techniques in other satellites, such as the Sentinels of the European Space Agency, to quantify the ascent near the coast, especially in populated areas.
What are the consequences of sea level rise?
From increasing floods during storms to the forecast that there will be areas of the planet that will live in permanent immersion. In addition, these rises erode the coast and salinize the aquifers [reservas de agua dulce].
Is there an island that has disappeared or is about to do so?
How can we control the rise in sea level?
We can not stop it. But we can reduce its intensity in the future if we emit less greenhouse gases into the atmosphere.
What should governments do?
Administrations have to implement the use of carbon-free energy sources as quickly as possible and reduce CO2 emissions as much as possible. And for this they must create public policies aimed at promoting public transport, for example. Since the Paris agreements, in 2015, there have been many delays in this regard.
What can citizens contribute?
The citizens must save energy and they can contribute in their scale, having an ecologically responsible behavior.