Weather Bee | Does the end of El Niño signal a lull in global temperatures? - Hindustan Times
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Weather Bee | Does the end of El Niño signal a lull in global temperatures?

Apr 10, 2024 08:34 PM IST

Analysis of the ONI and temperatures shows a weak correlation, indicating that the end of El Niño may not result in immediate cooling of global temperatures

In recent months, every update to the forecast for the El Niño-La Niña cycle (periodic warming and cooling of sea-surface temperatures in the equatorial Pacific) has increased the probability of a La Niña taking place in the June-September Indian monsoon season. This expected transition from the ongoing El Niño to La Niña was a key reason private forecaster Skymet Weather said on April 9 that the 2024 monsoon is most likely to witness "normal" rainfall. Will this transition to a cooling of the Pacific Ocean also decrease the warming in global temperatures seen in the past year? The answer to this question is not as simple as the relation between El Niño and monsoon suggests.

There is reason to suggest that the end of the current El Niño cycle may not halt the warming seen in the past year in global temperatures, at least not immediately (File photo) PREMIUM
There is reason to suggest that the end of the current El Niño cycle may not halt the warming seen in the past year in global temperatures, at least not immediately (File photo)

The relation between the El Niño-La Niña cycle and the monsoon is well known. HT reported on this last year when El Niño was taking effect at the start of the monsoon season. This analysis showed that while an El Niño does not always bring drought-like conditions, it produces a strong probability of a deficit in rains. This was also seen last year, when an El Niño-affected monsoon season ended with a 5.6% deficit compared to the 1971-2020 average, currently considered the Long Period Average (LPA) by the India Meteorological Department (IMD). A 5.6% deficit of LPA met the IMD criteria of “below normal” rains, which is classified as a deficit in the 4%-10% range.

This relation of El Niño with dry weather suggests that it should also lead to warmer temperatures. While that may be true, there is reason to suggest that the end of the current El Niño cycle may not halt the warming seen in the past year in global temperatures, at least not immediately. Here is why.

The El Niño-La Niña cycle is tracked using the Oceanic Niño Index (ONI). ONI is also a type of temperature index, where increasing values imply warming. When the three-month running mean of ONI is 0.5°C or higher for at least five consecutive months, an El Niño is said to have taken hold. The chart below shows the warming in global temperatures (relative to a pre-industrial average) alongside the ONI since the current El Niño started. This shows that the warming in air temperatures (which is the usually reported temperature) was increasing every month when ONI was increasing, as expected. However, the level of warming in air temperatures has remained relatively flat despite the ONI rapidly decreasing after December. This is one reason why one must not expect warming in global temperatures to ease immediately after the El Niño ends. The explanation usually given for this is that it takes time for cooling on the ocean surface (which ONI measures) to transfer to global air temperatures.

 

While the chart above tracks only the current El Niño cycle, the trend it describes can also be seen in data for a longer period. HT compared the 12-month running mean of ONI with the 12-month running mean of global warming. This shows that there is a very weak correlation between the two. Global temperatures have increased and the warming became more rapid over time although El Niño has affected only 26% of the months from January 1979, the period analysed here. This acceleration in global warming is another reason why one must not expect temperatures to cool down after the current El Niño is over. Accelerated warming can offset any cooling benefits of La Niña.

Abhishek Jha, HT’s senior data journalist, analyses one big weather trend in the context of the ongoing climate crisis every week, using weather data from ground and satellite observations spanning decades.

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  • ABOUT THE AUTHOR
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    Abhishek Jha is a data journalist. He analyses public data for finding news, with a focus on the environment, Indian politics and economy, and Covid-19.

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