El Niño

By: Sarah McGhee, UHM MOP Student

El Niño and La Niña are cycles of cooling and warming in oceans across the globe, however little is known about the effects they have on the ocean and its inhabitants. We know an El Niño affects ocean temperatures, currents, and even weather on the shores across the world. The cycles and ?routines?of the warming and cooling periods are hard to track and even harder to predict. However, with scientists predicting an El Niño within the next year, ocean life, such as coral reefs, may be facing a new threat.

The El Niño phenomenon is part of a much larger event known as the El Niño-Southern Oscillation (ENSO). Exacerbated by climate change, the El Niño is the warming period in this cycle. Coastal upwelling is the process in which warmer waters are pushed along the Pacific by trade winds. When the trade winds weaken, the warmer water moves less, leading to the warming period. In a La Niña the opposite occurs, more trade winds blow, and a ?cooling? period occurs. Predicting these cycles is not an easy task and little is known about what may trigger different periods. Climatologists working in the early 1900?s learned that the El Niño occurred at the same time as the Southern Oscillation, meaning as the ocean water temperature increased, the atmospheric pressure above the ocean decreased. It was believed that an El Niño or La Niña event occurred every two to seven years. However, as climate change becomes more drastic and the ocean warms, the events may become more frequent or more extreme.

But what does the warming and changing of cycles mean for the animals that call the ocean home?

Specifically looking at coral reefs, which are greatly affected by warming temperatures, even a slight increase in ocean temperatures causes an event known as coral bleaching. When water temperatures get too warm, corals expel their zooxanthellae, the algae that produces the coral's nutrients and color, resulting in bleaching. If the temperatures do not return to a comfortable level, the coral will likely not recover and die. Coral reefs provide shelter for a number or species across the Pacific. As a result, mass coral bleaching events are also detrimental to fish populations. With the prediction of an El Niño later this year, scientists are already concerned for the fate of some reefs.

The most extreme El Niño of the 20th century occurred in 1982-1983, where in some parts of the Eastern Tropical Pacific, surface temperatures increased 9-18 degrees F above normal. The El Niño event in 2015-2016 triggered the worst global bleaching event and mass mortality of coral to date. While scientists as NOAA are not predicting an event as detrimental as this, the effects cannot be ignored. Their predictions estimate an 80%chance of a moderate El Niño, with surface temperatures increasing by 1.8 degrees F from normal. Even small changes can influence coral reefs, who rely on constant temperatures to survive. While we as people cannot control the ENSO cycles, we can help to mitigate the effect climate change has on the cycle and the life it affects. Millions of people rely on the fishing and tourism industry in all parts of the world, where coral reefs are the backbone of their livelihood.

Understanding the role we all play in ocean health is the first step toward ensuring the longevity of our reefs.