This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Residents of Te Whanganui-a-Tara Wellington know it is always wise to prepare for any weather—to pack sunglasses, a raincoat and at least one extra layer. This "be prepared for anything" approach can equally be applied to Aotearoa's ocean weather during this year's "super" El Niño.
Forecasts are fickle, unexpected outcomes are likely and preparation is needed. El Niño and its opposite phase, La Niña, are natural climatic features caused by swings in atmospheric pressure over the Pacific. Typically, trade winds over the central Pacific blow from the east, drawing cold, nutrient-rich water from the deep ocean to the surface off the western coast of South America in a process called upwelling.
But during an El Niño phase, a reversal in atmospheric pressure over the Pacific causes trade winds to weaken or reverse entirely. Without easterly winds, upwelling does not occur. Instead, warm, tropical surface waters accumulate in the eastern Pacific and release heat into the atmosphere, increasing air temperatures.
El Niño phases vary in strength, but the El Niño currently building in the Pacific is on track to be the strongest recorded. Ocean temperatures in the central Pacific are forecast to reach new heights this summer—potentially 3.6°C hotter than normal. Air temperatures in the coming year will likely reflect these extremes.
Temperature hikes may be particularly dramatic because this El Niño is occurring against a backdrop of warmer-than-normal air and ocean temperatures caused by climate change. To understand the range of possible effects on Aotearoa's coast and marine life, we can look at similar past events. The last strong El Niño was about a decade ago in 2015–16, with prior strong events in 1982–83 and 1998–99.
Taken together, these events provide a good picture of what will happen on land—stronger, more consistent westerlies throughout the summer, heavier rain along the west coast and heightened drought and wildfire risk along the east coast. In the ocean, however, the picture is less clear, and ecological effects will likely be mixed. Unlike El Niño effects in the eastern Pacific, these phases typically bring slightly cooler-than-average sea surface temperatures to Aotearoa.
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