Skip to 0 minutes and 0 seconds(plucked string arrangement)
Skip to 0 minutes and 25 secondsSince about three decades, satellites monitor routinely the ocean. We have hydrometers on both satellites that measure the evolution of sea surface temperature. We have also satellites that measure sea surface salinity, for example a small satellite launched some years ago by the European Space Agency. Satellite altimetry, it's a major technique now that measures the sea surface topography from which we derive ocean currents and sea level rise, of course. We have multispectral imageries that measure ocean color. Quantities that give us information about phytoplankton concentration and information on marine ecosystems, and space gravimetry, a technique that measures the changing mass of the ocean. Used for example to learn the ice melt or directions of weather on which continents.
Skip to 1 minute and 28 secondsSatellite altimetry is a whole technique. The first satellite was launched in the mid '70's, however, we had to wait until the beginning of the '90's with the launch of the TOPEX/Poseidon mission developed jointly by NASA in the United States and CNES in France. And this date really marks beginning of high-precision altimetry. And the beginning of oceanography from space. So this mission followed by many others,
Skip to 2 minutes and 1 secondJason-1 Jason-2, Envisage from ESA Cryosat also from ESA. All these mission are now routinely used to derive sea-level rise. A very important parameter with the new generation of altimeter satellites. We are able to measure the sea surface height with the position of one to two centimeters. Which is absolutely incredible. Compared to the previous mission for which the uncertainty to a sea surface height measurement was in the order of several decimeters. High precision satellites altimetry, show us that the sea level is rising. At a rate of about 3.3 millimeters per year. In terms of global mean. We have clear evidence that the global mean sea level is rising.
Skip to 3 minutes and 0 secondsAnd compared to what we know from the previous decades, based on tide gauge observations. We observed that there is an acceleration of about a factor of two. Since the beginning of the '90's compared to the previous decades. So because we have at our disposal a number of observing systems, we can also quantify the cause of this global mean sea-level rise. So there are two main causes. One is ocean warming. Because the ocean is warming, the sea water is expanding. So the sea level is rising, so this is one cause. And the second contribution is land-ice melt. And that is an important observation made by altimeter satellites is that sea level is not rising uniformly.
Skip to 3 minutes and 56 secondsAnd in some regions for example the Western Pacific, the Indian Ocean, north of Australia, sea level has been rising at a rate three to four times larger or faster than the global mean rise. For example in the Philippine region, since the beginning of the '90's the sea level has been rising by more than 25 centimeters. Which is a huge number. And we know now that non-uniform thermal expansion is the main cause of this regional variability in the rate of sea-level rise.
Skip to 4 minutes and 36 secondsHow much the ocean will change in the coming decades will really depend on the future of greenhouse gasses emission. If we continue to emit carbon dioxide and methane at the same rate as today, for example the global mean sea level will be higher than it is today by let's say around 75 centimeters. By 2100. And it is already the case now, there will be important variability, regional variability around this number. In particular it is expected that the Arctic will be even more elevated as well as the tropics. We expect an amplification by about 30%.
Skip to 5 minutes and 33 secondsAbove the global mean rise. If we decide at the COP21 to reduce greenhouse gasses emission, following the two degree sea warming target, in that case even with zero emission at the end of this century, sea level will be rising and we in that case what climate models simulate is an elevation compared to today of about 40 centimeters. But we see that even in that case, sea level will rise. And this is because of two factors, one is the thermal inertia of the ocean. That have already committed to about 33% of the heat excess stored in the climate system since a few decades because of human activities, because of greenhouse gasses emission.
Skip to 6 minutes and 37 secondsAnd the second factor is the long lifetime of carbon dioxide. These numbers are the position of climate models, but beside the climate projection we clearly need to continue the observation. To see how all the climate system is evolving. And if the projection, prediction, are in line with the observation. It is absolutely fundamental that we have a sustained observing system in particular from space. If we do nothing in terms of greenhouse gasses emission, as far as the ocean is concerned what we are expecting is a increase of ocean temperature, increase of ocean acidification which has a negative impact on marine life.
Skip to 7 minutes and 24 secondsDecrease of the oxygen also which has a very negative impact on marine life, and because the ocean is becoming warmer, sea level will be rising.
Skip to 7 minutes and 38 secondsSo there is no other solution than decreasing our greenhouse gasses emissions and turning towards other energy sources.
Ocean Monitoring from Space - Introduction from Professor Anny Cazenave
Professor Anny Cazenave, a leading expert in Earth observation and climate science, presents a special introduction to the role of satellite technology in monitoring the world’s oceans.
(Subtitles and transcripts for this video are also available in Spanish and Chinese. Just click on the small pink square in the video controls to select your preferred language, or download transcripts from the bottom of this page).
Professor Anny Cazenave
With thanks to Cité de l’Espace, Toulouse.