El Niño and La Niña are opposing Pacific Ocean weather patterns that affect the global climate and ocean temperatures. El Niño causes weakening trade winds and periods of unusually warm ocean temperatures. In comparison, La Niña is a cold event defined by strong trade winds and a drop in ocean temperatures. Both weather patterns typically occur every two to seven years and last between nine to twelve months. Although climate researchers cannot yet confirm whether El Niño will certainly happen, the weakening winds observed along the equatorial Pacific Ocean and the increased temperatures beneath the ocean surface have raised alarms. Research indicates that the next El Niño event could begin later in 2023, potentially by July.

Global implications – The global effects of El Niño are observed in unusual weather patterns that have far-reaching implications. The Americas, northern US and Canada typically experience dryer, hotter summers, and severely cold winters. The US Gulf Coast, Ecuador and Peru experience increased rainfall, leading to coastal flooding and erosion. Southern Europe gets wetter weather during an El Niño event, while northern Europe experiences dryer and colder winters. Australia, India, and Indonesia generally have less rainfall which leads to droughts and wildfires.

Threat to the Pacific – Pacific islands are extremely vulnerable to the effects of El Niño. During the particularly strong 2015 event, 4 million people in the Pacific faced hunger, poverty, and disease as a result of increased droughts and floods. Sea levels can rise by up to 0.5m in Indonesia due to hotter trade winds and expanding warm water. Whilst central Pacific regions such as Kiribati and Tuvalu are also expected to experience flooding and higher sea levels. With a maximum elevation of 2 metres (excluding the volcanic island of Banaba) and several islands already lost to the ocean, Kiribati is thought to become the first casualty of climate change.

Upwelling ocean, declining anchoveta – El Niño warms the surface of the Pacific Ocean, reaching up to 3C above average off the coast of Ecuador and Peru. This deepens the thermocline, the depth at which warm and cold waters separate. The thermocline dictates the upwelling of cold, nutrient-rich water upon which healthy ecosystems thrive on. Without this upwelling, plankton and other photosynthetic species populations decline, having knock-on effects throughout the food chain. In Peru, this drastically reduces anchoveta numbers. At its peak in 1971, Peruvian fisheries netted 17 million tonnes of anchoveta, reduced to 3.3 million tonnes in the 2015 El Niño year. Many are concerned that this fish stock, known as the “most heavily exploited fish in world history”, could collapse without careful governance.

Coral bleaching – Coral reefs are also vulnerable to warmer temperatures. These ecosystems are home to a quarter of marine life despite occupying only 0.1% of the ocean floor. The services coral reefs provide to humans have been valued at over £300bn a year, sheltering coastlines from storms and feeding millions. During the last El Niño event, 30% of the world’s coral reefs were lost as warmer water forces the release of their life-sustaining zooxanthellae. This is known as coral bleaching, leaving behind only white skeletons. Corals take decades to recover and can only do so when temperatures return to normal. A study, however, did find some species that can regenerate during marine heatwaves, providing some promise for the future of coral reefs.

Previous El Niño events – El Niño has wreaked havoc for humans for centuries. Between 30 and 60 million died during The Great Drought in 1876-78, which scientists have linked to El Niño. More recently, the 1982 El Niño, thought to be the strongest on record, caused up to $8bn in damages and drove several species to extinction. Although agriculture and healthcare have advanced since the 1800s, so too have global temperatures and natural disaster frequency and intensity. In the past century, for example, the occurrence of natural disasters has increased 10-fold, causing an estimated $383 million worth of damage every day over the past decade. Without action on emissions, it is likely that natural phenomena such as El Niño cycles will become increasingly disruptive to humans and wildlife.

Source: Mongabay