El Nino Labelling and the Natural Cycle
Context:
Scientists have recently updated how they label El Nino and La Nina events.
The US National Oceanic and Atmospheric Administration (NOAA) has altered its calculation methods to account for rapidly rising global ocean temperatures caused by climate change.
This change is likely to result in more events being classified as La Nina and fewer as El Nino in the future
The Natural Cycle (ENSO):
The El Nino/La Nina cycle is a natural oscillation of the ocean-atmosphere system in the Pacific Ocean that occurs every 3-7 years.
Together, they are called ENSO, which is short for El Niño-Southern Oscillation.
The ENSO pattern in the tropical Pacific can be in one of three states:
El Niño (the warm phase)
Neutral Phase
La Niña (the cool phase)
Trade winds blow from east to west, piling warm water up in the western Pacific (near Australia) and causing cold, nutrient-rich water to upwell off the coast of Peru.
El Nino:
El Niño means Little Boy in Spanish
Trade winds weaken.
Warm water flows back toward the eastern Pacific, suppressing upwelling.
This often leads to warmer global temperatures and altered weather patterns.
Rising air motion (which is linked to storms and rainfall) increases over the central or eastern Pacific.
Meanwhile, an increase in sinking air motion over Indonesia leads to higher surface pressure and dryness
Rainfall is below average over Indonesia and above average over the central or eastern Pacific.
La Nina:
Trade winds strengthen, pushing warm water further west.
Most of the tropical Pacific Ocean is cooler than average.
This exposes cooler waters in the east and typically depresses global temperatures.
Rainfall increases over Indonesia (where waters remain warm) and decreases over the central tropical Pacific (which is cool).
Over Indonesia, there is more rising air motion and lower surface pressure.
There is more sinking air motion over the cooler waters of the central and eastern Pacific.
Why the Label Change?
Shifting Baseline:
As global waters warm due to climate change, the threshold for what constitutes "unusual warming" (El Nino) has shifted.
The new labelling adapts to this hotter baseline.
Energy Imbalance:
A recent study attributes the sharp spike in Earth's temperature to a combination of human-caused climate change and the shift from a "triple dip" La Nina (2020-2023) to an El Nino.
During the "triple dip" La Nina, warm water was trapped at deeper depths, reducing the heat emitted into space (similar to a body holding in a fever).
When the cycle flipped to El Nino, this stored heat was released, exacerbating the energy imbalance.