Credits: AVISO/CNES/CLS 2015.
Spot the differences! El Niño is visible in red in these images of sea level anomalies. The image on the left is derived from observations by the French-U.S. TOPEX/Poseidon satellite in November 1997 during the “El Niño of the 20th century”. The image on the right is a compilation of measurements acquired in November 2015 by Jason-2, SARAL-AltiKa, HY-2A and Cryosat.
There are many similarities, but the 2015 anomaly has only partly reached the South American coastline: it is not quite as intense as the 1997 episode... for now. But what will it look like in December?
A big El Niño turns the globe’s weather patterns topsy-turvy, bringing drought to some regions and torrential rains and massive cyclones to others. During the winter of 1997-1998, the wild child of the Pacific impacted 110 million people, triggering storms and floods that left 24,000 dead and $40 billion in losses to crops and fisheries according to United Nations figures.
El Niño also affects temperatures worldwide. It is partly responsible for last October’s monthly anomaly 1.04°C above the long-term average for 1951-1980, a new record.
How do satellites spot an El Niño?
The warm temperatures just below the surface that come with an El Niño cause the sea level to rise as water molecules expand. Altimetry satellites are able to pick up this ‘bulge’ and track its progress eastwards towards the coasts of South America. During an intense episode like the current El Niño, the sea level is 25 cm above the average across the Pacific basin.
“The early signs of an El Niño appeared very early this year, in March,” says CNES altimetry satellite expert Emilie Bronner. “An El Niño event also looked likely last year but it died down after a few months. This year, it has kept strengthening and we expect it to peak at the end of December and then disappear next spring.”
DID YOU KNOW?
As a result of global warming, extreme El Niños could become twice as frequent in the 21st century—one every 10 years against one every 20 years in the last century—according to a research paper published in Nature Climatic Change in 2014. CNES is a key global player in satellite altimetry, working in partnership with the United States (on the TOPEX/Poseidon, Jason-1, Jason-2, Jason-3, Jason-CS and SWOT satellites), Europe (ERS, Envisat, Cryosat, Sentinel-3 and Sentinel-6), India (SARAL-AltiKa) and China (HY-2A).
CNES’s long heritage in altimetry
CNES’s pivotal role in the field of altimetry enables it to develop synergies between complementary ocean-observing missions while also intercalibrating instrument measurements. As Philippe Escudier, CNES’s lead ocean/cryosphere expert, points out: “a single satellite isn’t enough to map the oceans; you need 3 or 4 to obtain a resolution of 80 to 100 km.”