This visualization shows side by side comparisons of Pacific Ocean sea surface height (SSH) anomalies of what is presently happening in 2015 with the Pacific Ocean signal during the famous 1997 El Niño. These 1997 and 2015 El Niño animations were made from data collected by the TOPEX/Poseidon (1997) and the OSTM/Jason-2 (2015) satellites. Image credit: NASA’s Jet Propulsion Laboratory
El Niño is an unusually warm pool of water off the west coast of South America, usually arriving around Christmas time, linked with complex, large-scale interactions between the atmosphere and ocean in the Pacific.
If you live anywhere El Niño has important impacts, you’ve heard forecasters say this year’s event looks just like the monster El Niño of 1997-98.
NASA satellite images of the Pacific Ocean in November 1997 and November 2015 show almost identical, large pools of warm water in the eastern equatorial Pacific. The National Weather Service has forecast that impacts this winter will resemble those in 1997, when California and the U.S. South suffered floods, mudslides and tornadoes, while residents of the Upper Midwest saved $2 billion to $7 billion in heating costs throughout their unusually warm winter.
When it comes to El Niños, however, there are no identical twins. This year’s event hasn’t always resembled the ’97 one. Satellite observations from early ’97 and early ’15 show conditions in the Pacific Ocean that were, well, oceans apart.
In its “normal” state, the Pacific is warm on the western side and cooler in the east. That’s what the ocean looked like in 1996 and early 1997. Conversely, over the past 18 months or so, satellite images have shown a large pool of warm water hovering around the equator in the central Pacific — neither west, as in a normal year, nor east, as in a typical El Niño. Tong Lee is an oceanographer at NASA’s Jet Propulsion Laboratory (JPL), in Pasadena, California. Lee said:
That warm patch started last year and it never disappeared. It’s very peculiar behavior.
In the first decade of the 2000s, scientists began noticing that warm pools were appearing more frequently in the central equatorial Pacific. Since they look like El Niños but are in the wrong place, some began calling them “central Pacific El Niños.” Others use the name “El Niño Modoki,” Japanese for (roughly) “almost but not quite an El Niño.”
Michelle Gierach studies the ocean response to El Niño at JPL. She said:
Whether we have [different] flavors of El Niño, central versus eastern Pacific El Niños, or a continuum is an actively debated topic.
However it’s classified, the central Pacific phenomenon tends to have different global impacts than the classic El Niño variety. In the United States, a strong, classic El Niño usually heralds a warmer Northwest and colder Southeast. The central Pacific version is associated with a warmer Northeast and colder Southwest.
But the central Pacific isn’t the only part of the ocean that has been behaving oddly in the last few years. Gierach said:
Before the developing 2015 El Niño, there was prolonged anomalous warming off the West Coast of North America called the Blob.
Named by Nick Bond at the University of Washington, Seattle, the Blob is the largest pool of warmer-than-normal water in the North Pacific Ocean in recorded history. It formed about two years ago near the Gulf of Alaska and grew to span the entire U.S. West Coast, merging with warm pools off Baja California and in the Bering Sea. Gierach said:
The occurrence of this phenomenon in association with El Niño is not normal, based upon our satellite record, and the combination of the two has greater potential to affect marine life.
Wherever El Niño warms the ocean, it reduces the nutrients upwelled from the ocean depth. From satellites, this can be seen in declining concentrations of sea surface chlorophyll, a green pigment found in phytoplankton. These microscopic plants are the lowest level of the ocean food web. Gierach said:
Phytoplankton, like people, have environments that they favor.
Just like any other plant, they like specific light conditions, temperatures and nutrients. When those conditions change, phytoplankton species change as well. That cascades up through the marine food chain. These changes in phytoplankton, fish and other marine life have already been observed in association with both the Blob and El Niño.