This blog was written by Michele Conrad, advisor to Ocean Conservancy on achieving priority fish conservation and ecosystem goals on the West Coast. As a former state ocean policy manager, Michele represented the State of Washington on the Pacific Fishery Management Council for 15 years before starting her own consultancy. She is passionate about helping fisheries manage their way through climate change and furthering ocean conservation efforts.

The Climate Prediction Center of NOAA’s National Weather Service recently issued an El Niño watch, forecasting its appearance sometime between May and July with a 90 percent chance it will persist into 2024. This news makes me uneasy because El Niños traditionally wreak havoc with the climate. In fact, the forecast of an El Niño is like learning an unpredictable and disruptive guest is coming to visit. 

With recent ocean temperatures already at record-high levels, I wonder what an El Niño will mean for fish now—and for the future. In the best of times, this guest tends to stay for nine to twelve months, eat all the food, destroy the garden, and wreak havoc on the neighborhood. But we have yet to experience El Niño in these warmest of times.

Let me explain why I have such a negative attitude toward this particular visitor. 

When we think about the connections between people and fish, we typically think about fish as food. This isn’t surprising since the United States consumes more than 6 billion pounds of seafood per year, averaging 19 pounds of seafood per person and ranking as the second-highest nation in overall consumption (China is the highest). But while more than 3 billion people worldwide rely on seafood as a major food source, even those who do not consume fish depend on them because of their essential role in marine ecosystems. Fish are the lifelines that keep the marine food web intact. 

It’s not surprising then that fishers were early observers of El Niños. Marine ecosystems are dynamic, and, while we have much to learn about some ecological processes and relationships, the climate condition known as El Niño has been observed by Peruvian fishers for centuries when warm ocean waters would appear along the coasts of Ecuador and northern Peru every two to seven years and cause the fish to disappear. The name El Niño (or “the child”) comes from the fact that these conditions would tend to start around Christmas time (hence, “the child”). I imagine that those fishers who relied on fish to feed their families and communities viewed this warm water occurrence in a similar way—like an unwelcome guest. 

In the 1920s, scientists realized that these South American ocean-warming events were part of a broader cycle (called the El Niño-Southern Oscillation or ENSO) in which warmer ocean waters (El Niño) alternate with periods of cooler waters (La Niña) on an irregular schedule. As departures from neutral climate conditions, both El Niño and La Niña events affect climate and weather around the world with hurricanes, droughts and warm ocean temperatures in the Pacific, Atlantic and Indian oceans.

As carbon dioxide emissions quickly accelerated over the past 75 years, 90 percent of the heat caused from those emissions has been absorbed by the ocean. ENSO is an important phenomenon that transports heat from the tropics to higher latitudes—a process that is necessary to maintain long-term global climate stability. But with global warming, there is a lot more heat to transfer, and, with the rapid rate that heat is accumulating, it must be transferred faster, more frequently and for longer periods of time.

While each El Niño event is different, scientists have identified common traits and can reliably predict resulting effects on marine ecosystems. Among other things, El Niño essentially stops upwelling along the equator and the west coast of South America, and in regions like the U.S. West Coast—a process that allows deeper, colder (and nutrient-dense) water to rise to the surface of the ocean. Upwelling brings deep and nutrient-rich waters to the surface that can help the base of ocean food webs, phytoplankton, flourish and grow. These microorganisms are essential components of the marine ecosystem, transporting nutrients to fish and plants. Not only do they provide food for fish, but through photosynthesis, plants such as phytoplankton, kelpand algae absorb 25 percent of all CO₂ emissions worldwide and produce 50 percent of the world’s oxygen–much of which is used to sustain marine life.

El Niño also brings marine heatwaves, which are periods of extreme warm ocean temperatures at the surface or along the seafloor that can severely disrupt ocean ecosystems. With climate change, marine heatwaves are becoming more frequent, intense and persistent even with cooler waters, and the frequency and intensity tends to increase when El Niño arrives. Marine heatwaves along the seafloor can be more intense and persistent than those at the surface, seriously impacting fish populations like snow crab in the Bering Sea, which declined by 90 percent after an intense heatwave in 2018. Marine heatwaves also increase the likelihood of harmful algal blooms, which produce toxins that affect shellfish, seabirds and other wildlife, and can be harmful to humans. To make matters worse, as these algal blooms decompose, that process uses oxygen faster than it is replenished, causing low oxygen levels in the water and harming marine life.

In a nutshell, El Niño can cause a host of changes to ocean conditions that impact ocean ecosystems and fish, and for centuries, fishers accepted El Niño’s appearance as part of a natural balancing cycle. They knew, too, that El Niño brought rain to arid inland areas, a reason that El Niño years were also known as “años de abundancia.” Knowing that the visit was temporary and looking forward to a future visit from La Niña helped make the stay endurable. The counterpart to El Niño, La Niña typically brings increased upwelling, producing colder waters with higher nutrient levels. The ocean has had record-high temperatures for the past eight years with each one higher than the last—and La Niña was here for half of those. Scientists used to think that La Niña could offset warming, but now it is clear that isn’t the case. 

In 2022, the warmest year on record for the Northeast Pacific, the U.S. West Coast experienced strong coastal upwelling through the spring consistent with La Niña condition.  however, the winds shifted in June and stayed that way through the summer, rapidly reversing any above-average gains in productivity.

So, what will El Niño bring this year and what does this mean for our future?

To gain a better understanding of what lies ahead, NASA is using satellite data to map the presence of phytoplankton and study the impacts of El Niño on the marine food web and fish populations. NOAA’s Integrated Ecosystem Assessment Team also monitors key indicators in marine ecosystems, evaluates how that system is connected and changing, and produces annual ecosystem status reports to inform fisheries managers of these connections and changes. Hopefully, through these efforts, we can offset some of El Niño’s effects and—by working together to globally address climate change—see a day without fearing future visits.