By: Dana Sackett (with awesome edits by Troy Farmer)
Most of us have probably heard the term El Niño. But what exactly is El Niño and what impact does it have on our oceans and climate? Another important question to ask is: what can we expect from El Niño in a future with a warmer climate and ocean? In this week’s article I attempt to answer some of these questions and give you an idea of what is currently happening to our oceans and the world as a result of El Niño.
El Niño is one half (La Niña being the other half) of a complex weather pattern called the El Niño-Southern Oscillation (ENSO) cycle that occurs at irregular intervals (approximately every two to seven years), lasts somewhere between 12 to 18 months, and causes deviations from normal ocean temperatures across the Equatorial Pacific. When the deviation is warmer than normal waters extending across the Equatorial Pacific (because of weakened trade winds) this is called El Niño, when the deviation is colder than normal waters extending across the Equatorial Pacific (because of strengthened trade winds) this is called La Niña.
The trade winds I mentioned above are winds that are usually present along both sides of the equator. Under normal conditions, trade winds steadily push shallow, warm Pacific surface waters from east to west (that is, away from Central and South America, towards Indonesia). This allows deep, cold water in the eastern Pacific, which has accumulated lots of nutrients from sinking particles over time, to come up to the surface to replace the warmer water being pushed westward by the winds (this is called upwelling).
An El Niño can have a number of serious impacts around the globe, with altered weather patterns being the most obvious. The movement of so much warm water into the eastern Pacific increases evaporation, supplying more water vapor to the atmosphere, resulting in a lot more rain. This is particularly true for Japan, and the western side of North and South America, and troublesome for regions that are typically dry and ill-equipped to deal with heavy and long-term rain. For example, El Niño has likely contributed to the major flooding in Texas over the past year. In addition to flooding, severe drought and intense heat waves also occur during El Niño events in other areas (for example in Australia, Indonesia, East Africa, and various parts of the United States).
For the normally abundant fisheries, (for example, anchovy, tuna, hake, salmon, and cod), along the eastern Pacific coast, El Niño can be devastating. Many of the fisheries along this coast rely on the upwelling of deep cold nutrient-rich water to fuel the food web. During El Niño, upwelling declines or even stops along the coast of South America, cutting-off that source of fuel. This forces fish and marine mammals to search elsewhere for food or starve. Further impacting tropical fisheries and ecosystems, corals will begin bleaching when ocean temperatures become too warm. This can result in large stretches of dead coral reef, decimating the fisheries and species that rely on those coral reefs to survive.
However, not all El Niño events are equal. Some have had little overall impact on the environment, while others are more severe with devastating consequences. Two such El Niño events occurred during 1982-1983 and 1997-1998, causing severe flooding and landslides in the southwestern United States and Peru, abnormally cold weather in Europe, major droughts in Australia, Indonesia, China, India, Africa, and Central America. These events also caused widespread bleaching of corals across the equatorial Pacific Ocean and the collapse of food chains across the eastern Pacific coast.
The El Niño event we are currently experiencing began in late 2014 and is just beginning to show signs of weakening. With ocean temperatures already on the rise due to climate change, the current El Niño has hit coral reefs hard. In fact, 2015 marked the third and longest global coral bleaching event on record, and this El Niño isn’t over yet. For the Great Barrier Reef, this warming has been devastating. In a recent examination of the Great Barrier Reef only four of 520 surveyed reefs had no bleaching.
While corals of the Great Barrier Reef have adapted to deal with naturally occurring warming cycles like El Niño, the severe warming from the current El Niño appears to have exposed much of these reefs to temperatures above the corals’ lethal limit. Even more worrisome, some scientists have suggested that climate change could cause El Niño events to become more frequent, amplifying future coral reef bleaching as well as many of the other impacts climate change is already having on our ocean ecosystems.
On a lighter note we did find a demonstration by Chris Farley on how powerful El Niño can really be… (for all those 1980’s and 1990’s pro wrestling fans)
Chris Farley demonstrates the true power of El Niño in this classic SNL skit. To see the whole skit go to http://www.nbc.com/saturday-night-live/video/el-nino/2861308
References and other reading material:
Ainsworth, T.D., Heron, S.F., Ortiz, J.C., Mumby, P.J., Grech, A., Ogawa, D., Eakin, C.M. and Leggat, W., 2016. Climate change disables coral bleaching protection on the Great Barrier Reef. Science 352:338-342.
Di Lorenzo E, Cobb KM, Furtado JC, Schneider N, Anderson BT, Bracco A, Alexander MA, Vimont DJ. 2010. Central Pacific El Nino and decadal climate change in the North Pacific Ocean. Nature Geoscience 3:762-765.
McPhaden MJ, Zebiak SE, Glantz MH. 2006. ENSO as an integrating concept in earth science. Science 314:1740-1745.
Niquen M, Bouchon M. 2004. Impacts of El Nino events on pelagic fisheries in Peruvian waters. Deep Sea Research Part IIL Topical Studies in Oceanography 51:563-574.
Schneider N, Di Lorenzo E, Cobb K, Anderson BT, Vimont DJ, Alexander MA. 2016. Pacific decadal variability and central Pacific warming El Nino in a changing climate. Final Report DE-SC0005111, Regional and Global Climate Modeling (RGCM) Program.