El Nino later this year could make it likely the world will exceed 1.5C of warming in 2024

The forecast return of El Niño later this year could make it likely the world will exceed 1.5C of warming for the first time in recorded history, more likely in 2024 as the warming of the world’s atmosphere by El Niño will take a number of months. The hottest year in recorded history, 2016, was driven by a major El Niño.

The first "triple-dip" La Niña event of the 21st century is over, and the odds of an El Niño in the tropical Pacific Ocean this year, perhaps as early as this summer, are rising.

La Niña is the phase of the El Niño Southern Oscillation (ENSO) where waters in the Pacific Ocean are cooler than average, the opposite of the warmer El Niño phase.

CFS seasonal SST forecast shows the tropical Pacific warming over coming months

The three-year La Niña event, which started in September 2020, doesn’t happen very often. Previous triple-dip La Niña events spanned the years of 1998-2001, 1973-1976, and 1954-1956.

The protracted La Niña event has caused droughts in North and South America and the Horn of Africa. La Niña is also linked to floods in Asia, such as the devastating floods Pakistan endured last year and also the severe and record-breaking flooding in eastern Australia last year.

In theory, the cool phase of ENSO tends to put a temporary brake on the increase in global average surface temperatures, preventing a new record-setting warm year. Yet each La Niña year has tended to be the warmest La Niña year on record, as human-emitted greenhouse gases influence the natural ENSO cycle.

2022 was the sixth warmest year on record globally, the global average temperature for 2022 was 1.16 °C above the pre-industrial baseline; 0.04 °C warmer than the value for 2021. But for the UK, 2022 was the warmest year on record, with an average temperature of over 10°C and 40°C recorded for the first time. This all despite the slight cooling influence of La Niña: a pattern of climate variability in the tropical Pacific that typically acts to suppress global temperatures.

Even those years with a temporary cooling influence from La Niña, such as 2022, are now much warmer than all years before 2015, even those that had been boosted by a warm influence from El Niño.

The concern is El Niño events release a tremendous amount of ocean heat into the atmosphere and would increase the odds for a new record warm year in 2024. The warmest year on record was in 2016 when a strong El Niño boosted global temperatures.

Comparison of temperature of a few years in recent past, note 2016 was the warmest and coincides with El Nino

During an El Niño, the ocean transfers excess heat and moisture to the atmosphere. On top of the global warming trend, a strong El Niño can add up to 0.2°C to the average temperature of the Earth. Since the planet has already warmed by around 1.2°C relative to pre-industrial times and El Niño adds some extra heat to the atmosphere, it’s possible that Earth’s rising temperature will temporarily exceed the 1.5°C threshold of the Paris agreement some time after the peak of the El Niño in 2024

It is likely that the effects of the recent three-year La Niña event will linger longer than usual, leading to continued dryness in the Horn of Africa and elevated risks of flooding in Australia and Southeast Asia. And with El Niño likely to occur later this year and during the northern hemisphere winter its heating effect may takes months to be felt, meaning 2024 is much more likely to set a new global temperature record than this year.

But when the warming effects of El Niño do arrive, not only could we see possibility of a new global temperature record, it may also trigger other extreme weather events. Australia has had three years of above average rainfall due to prolonged La Niña conditions that brought severe floods, especially in the east. During El Niño, scientists expect the opposite: less rain, higher temperatures and increased fire risk, especially during winter and spring in the southern hemisphere. Elsewhere, South American weather is significantly disrupted every time an El Niño event occurs, with flooding on the west coasts of Peru and Ecuador and drought in the Amazon and northeast.

As a result of global warming, scientists also expect El Niño’s influence over the North Atlantic and northern European winter may strengthen too, which could mean a weaker jet stream and surface pressure difference between Iceland and the Azores – with wetter conditions for southern Europe, colder and drier conditions for northern Europe.