The developing El Niño climate phenomenon is now the strongest on record, according to scientists monitoring Pacific Ocean temperatures. Daily sea surface temperatures in a key region of the central-eastern Pacific were 3.05C above average on 19 September - exceeding the previous record of 3.02C set during the very strong El Niño of 2015. Some longer-term measures of El Niño have not yet hit record levels but this is likely to change, with the peak not expected until later this year.
El Niño can cause major shifts in weather patterns around the world, with the Met Office saying many of the expected impacts are already being felt. El Niño set to be 'strongest in living memory', says Met Office What is El Niño and why could it mean record temperatures? El Niño is a naturally-occurring pattern, which happens about every two to seven years and tends to last for around a year.
Trade winds that typically blow from east to west across the Pacific Ocean can weaken or even reverse, allowing warm water to spread eastwards. Heat is then released from the ocean into the atmosphere which can boost global temperatures and drive changes in weather patterns around the world. Forecasters track the development of El Niño by watching temperatures in a key region of the Pacific Ocean.
When these are consistently 0.5C above normal, an El Niño is declared. There are different ways of measuring the strength of El Niño, however. The records that have now been broken relate to daily measurements of sea surface temperature compared with the long term historical average.
This is called the Oceanic Niño Index (ONI). Many scientists - including forecasters in the USA and Australia - also consider an alternative measure known as the Relative Oceanic Niño Index (RONI). This measures how warm the key El Niño region is relative to the rest of the tropical oceans, meaning it takes into account the background warming caused by climate change.
By the RONI index the current El Niño is not yet a record-breaker - but it is likely that more announcements will follow in the coming weeks. Professor Adam Scaife, Head of Long Range Prediction at the Met Office, said: "We have been signalling for months that the developing El Niño will be an unprecedented event. "The fact that it has already exceeded previous records – with several weeks to go before it peaks later this year – shows the enormity of this El Niño." Every El Niño is different, therefore impacts on global weather patterns are not guaranteed.
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