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Environmental impacts of El Niño

Published as part of an El Niño forecast and information microsite I designed in 2015 for Weather Underground, part of The Weather Company

During typical, non-El Niño seasons, coastal upwellings pull cold, nutrient-rich waters to the surface as tradewinds push warmer surface waters along the equator from Peru to Indonesia. Upwellings along the west coast of North and South America have the ability to sustain an incredible amount of marine life. In turn, warm waters in Indonesia trigger greater rainfall, allowing for higher crop yields, a pillar of Indonesian economy.

However, during an El Niño episode, upwellings diminish severely. Trade winds weaken, warm water stays along the South American coast and rainfall in Indonesia decreases. Fewer upwellings, combined with changes in sea surface temperatures and shifts in rainfall patterns during El Niño, often have negative impacts on the environment. 

Crop Failures

El Niño episodes typically disrupt harvesting seasons, whether that means flooding farmland in South Africa or extreme drought in Australia. Over 59 million people in India were touched by famine when monsoon cycle was disrupted by the 1899-1900 El Niño episode.

Ocean Sunfish in Alaska

Ocean sunfish were observed in 2014 and 2015 off the southern Alaska coast, hundreds of miles north of their usual habitat. The heaviest bony fish in the world, ocean sunfish prefer waters of 54°F or warmer. Crews from the Alaska Fisheries Science Center caught the large ocean sunfish pictured here. Source: AFSC, via NOAA.

Over time, erratic rainfall, flooding and drought have all contributed to massive crop failures in Africa, particularly affected sub-Saharan regions. Throughout the 2015-2016 El Niño season, maize production severely declined. Maize is not only a nutritional staple for citizens of sub-Saharan Africa, but it is also the economic center for many communities. South Africa’s harvest was especially impacted by severe drought exacerbated by El Niño. Traditionally an exporter of maize, South Africa had to import more than 300,000 metric tons of maize from Brazil in 2015.

Before and after coral bleaching

A before and after image of the bleaching in American Samoa. The first image was taken in December 2014. The second image was taken in February 2015 when the XL Catlin Seaview Survey responded to a NOAA coral bleaching alert. Source: XL Catlin Seaview Survey

Coral Bleaching 

Corals turn a solid white when the algae they depend on for life, become stressed and leave. This stress comes from changes in temperature, light or nutrients. During an El Niño event, coral reacts to this shift in ocean temperature by expelling the symbiotic algae that lives within its tissues. Once the algae is expelled, the coral is bleached and vulnerable to other harsh marine conditions.

While coral can recover from mild bleaching, severe or long-term bleaching is deadly. Once these corals die off, entire reefs quickly degrade and erode, leaving fewer habitats with shoreline protection for fish and other marine life.

The rising sea surface temperature during the 2015-2016 El Niño event endangered large areas of coral in the Hawaiian Islands. Other areas affected include Haiti, the Dominican Republic, Puerto Rico and the U.S. Virgin Islands.

Diminished Marine Life

Cold, nutrient-rich waters allow for a burst in marine life. However, when waters warm during El Niño episodes nutrient supply goes down, leading to progressively scrawnier plankton and microscopic-like creatures called copepods, the base species for the marine food chain.

Normally these plankton and later their predators, the copepods, are very fatty, giving nutrients to larger species on the food chain. In warm waters, upper level marine species are having to migrate long distances to find fattier prey.

Ocean sunfish, although tropical by nature, can often be seen off the coast of Alaska during an El Niño event. They migrate north along the Pacific coast, along with many other equatorial fish, in search of more amenable waters. Some species of crab will hide in deeper water, where it is colder and easier for them to survive.

Sea lion pups can’t get enough food, leading to a decline in the sea lion population. Jellyfish also have a tendency to die off during El Niño years because of a lack of nutrients.


California sea lion female and pup. Source: Tony Orr (NOAA)

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