The world’s rising climate temperatures and warming oceans have forced Earth Sciences New Zealand (ESNZ) to change the way it monitors the El Nino-Southern Oscillation (Enso) — one of our main climate drivers.
ESNZ meteorologist Chris Brandolino said Enso was a fluctuation of ocean temperatures and atmospheric pressure in the Pacific, and was made up of opposite phases — El Nino and La Nina.
The phases have a considerable impact on global weather, including in New Zealand.
Mr Brandolino said the warming seas and climate were interfering with the long-standing method used to monitor the ocean component of Enso.
"Traditionally, Enso is tracked by measuring how unusually warm or cool sea surface temperatures are in certain areas of the Pacific.
"However, as the climate warms, so do our oceans, which can muddy the Enso waters.
"As ocean temperatures increase, we can overstate the frequency of the warm phase of Enso (El Nino), and understate the cool phase (La Nina)."
He said during the 2024-25 summer season, the traditional index did not reach the threshold of -0.7°C to classify it as La Nina.
However, La Nina-like conditions were still observed across New Zealand, with above average air temperatures, widespread marine heatwave conditions and rainfall totals that were above normal in eastern areas and below normal in western areas.
As a result, ESNZ was following a move by the Australian Bureau of Meteorology and changing the way it calculated the sea surface temperature anomalies that help it track and forecast Enso.
He said they would now assesses how unusually warm or cool ocean temperatures are in specific locations, rather than use the tropical mean temperature.
"Had this been applied during summer 2024-25, the La Nina classification threshold would have been met, demonstrating how the updated methodology better reflects Enso impacts in a warming climate," he said.
