El Nino occurs when the ocean surface temperature in the tropical Pacific region rises above average. Because this water area becomes hotter than the surrounding area, the atmosphere will react, leading to changes in weather patterns. That is why El Nino, as well as La Nina, are always closely monitored by meteorologists.
Previously, El Nino was determined by the Oceanic Nino Index (ONI). Scientists compared the ocean temperature in a specific area of the tropical Pacific - called the Nino 3.4 region - to the 30-year average. The greater the difference, the stronger El Nino.
However, this method ignores the changes taking place in the rest of the tropical Pacific.
Global climate change has made the old method ineffective. The entire tropical Pacific is heating up rapidly to the point of covering up unusual signals caused by El Nino. As the ocean simultaneously heats up, identifying El Nino becomes more difficult.
Therefore, scientists have switched to a new measurement method: the RONI - Relative Oceanic Nino Index. This method uses a simple but effective calculation: Subtract the abnormal temperature level in the key area of El Nino from the abnormal level in the rest of the tropical Pacific.
This new approach basically eliminates the impact of climate change from the calculation, making El Nino easier to identify. Thanks to that, scientists can detect earlier and improve long-term weather forecasts.
Predicting and accurately identifying El Nino and La Nina is vital, because they can change the weather thousands of kilometers away, causing billions of USD in economic damage due to floods in one place and droughts in another, and affecting the Atlantic hurricane season.
Two leading experts in this field: Michelle L'Heureux of the US National Oceanic and Atmospheric Administration (NOAA) and Emily Becker from the University of Miami believe that the new index better reflects the interaction between the ocean and the atmosphere throughout the tropical Pacific.
El Nino and La Nina are boundary phenomena, meaning changes in the ocean will be accompanied by changes in the atmosphere.
Ms. L'Heureux pointed out that the general temperature is increasing across the Pacific Ocean, causing the old method to gradually lose its ability to recognize El Nino. "The old index is like looking at the Pacific Ocean through blurry glasses. Now we have the right glasses, so we can see El Nino/La Nina more clearly," she said.
Ms. Becker believes that climate change caused by humans is the cause of blurred vision.
“We have observed that in the past decade, the intensity of El Nino and La Nina, measured by the traditional Nino 3.4 index, is increasingly out of sync with actual weather impacts. Research shows that the reason is that the global ocean is heating up too fast, exceeding the reflectivity of the old measurement,” she said.
According to her, the new index better reflects the strength and weakness of these phenomena and their impact on weather, while eliminating the impact of the changing climate.
