What is El Niño?


In case Chris Farley failed to explain it adequately to you, let me talk you through what’s been happening since last fall.

Historically, every 7-10 years, the Pacific Ocean would experience a climatic anomaly lasting about 9-12 months, sometimes up to 2 years. Fishermen from off the West Coast of South and Central America would notice something changing around Christmas every so often. Accordingly, they started to call this phenomenon El Niño, after the Christ child. (In Spanish, el niño translates to “the boy” but the capital El Niño refers to Christ).

What was, and is still happening is a reversal of pressure systems. Usually, there is a low pressure system over Indonesia and high pressure system over the Eastern Pacific. This causes winds to move westward across the equator and are generally known as the Trade Winds. The Trade Winds move cold water from the eastern equatorial region of the Pacific west while they warm and cause evaporation. This evaporation forms into clouds which rain over the western equatorial Pacific. These winds also cause cold water to upwell, bringing cold water from the bottom of the ocean near South America to the top. So the eastern Pacific remains much cooler than the pool of warm water on the western edge. These waters typically bring with them loads of nutrients that have fallen to the bottom of the sea, increasing productivity near the coasts.


In El Niño events and episodes, these pressure systems weaken or reverse. Resulting in the Trade Winds dying down, upwelling to slow or cease, and warm water to span across the whole equatorial Pacific. This seemingly small climatic shift causes a cascade of events that warm the earth up to 10 degrees more than usual and disrupts rain patterns across the globe.


La Niña (the girl) events are the opposite and generally follow El Niño times. The low pressure system over Indonesia intensifies as does the high pressure system over the Eastern Pacific. The Trade Winds become stronger, the upwelling increases, and the warm water pool becomes much more concentrated and more western. This causes the earth to cool and again, for rain patterns to shift.


I should stress that El Niño events are perfectly natural. Symptoms of such events have been recorded deep into our history, so they themselves are not global warming. However, because the earth is already warmer, the extra degrees brought on by El Niño can prove catastrophic to many species, even humans. Additionally, these events are becoming more and more frequent and intense, now occurring every 2 to 7 years. Climate scientists do believe that the increased frequency is somehow related to human-created climate change.

From late summer, 2015 to the end of May 2016, we just experienced one of the top three most intense El Niño events recorded. Ocean temperatures across the globe were on average 9 degrees higher than usual, even in places not usually so affected by these events.

Coral reefs, already stressed by standard climate change, died in masses. Estimates of the Great Barrier Reef claim that up to 95% of the corals bleached, with 35% of the northern part of the reef now dead. Reefs across the tropics, from Madagascar to Indonesia, even the Caribbean experienced drastic bleaching events.


Reef building corals have a symbiotic partnership with zooxanthellae algae that live within their cells. The coral polyps can feed on microorganisms in the water, but they get most of their energy from these zooxanthellae converting the sun’s energy into food. The corals themselves don’t have much colour. Most are white or a cream colour. The zooxanthellae within their cells give them the beautiful colours we associate with the reefs. (These are the same algae that give giant clams and anemones their colour too.) But when a reef building coral is stressed, this partnership ends. The zooxanthellae leave the corals and what is left is the white/cream coral. This is where the term bleaching comes from.

Bleached corals are not dead. The zooxanthellae can return when conditions improve. But because the coral receives most of its energy from the algae, the coral doesn’t last for long on its own. It is also more susceptible to additional stressors. The warmer temperatures are hard for corals to survive, but the runoff caused by increased rains over fertilized farm lands and altered irrigation can deal the final blow. The overly nutrient saturated water causes algal blooms which smother the corals. Increased water temperatures will also lead to more frequent and more intense tropical storms which can wipe out entire reefs. Pollution and destructive fishing methods aren’t doing anyone any favours either.

‘What is El Niño?’ was written by Roya