Expert comment: How does El Niño affect global warming?

A key global warming limit is set to be surpassed within the next four years, new data from the World Meteorological Organisation shows. 

Rising carbon emissions are playing a part in the surge in temperature, but a weather pattern called El Niño also affects warming. 

Professor Richard Allan, climate scientist at the University of Reading, explains what El Niño is and what it does.

He said: “The substantial warming of the eastern Pacific Ocean as El Niño develops and the heat it releases to the atmosphere helps to make the world as a whole one or two-tenths of a degree Celsius warmer. But this actually causes the world to lose more heat as the warmer sea surface loses more energy to the air above and this energy is eventually lost to space as thermal infrared radiative emission. During La Niña, the reverse is true. However, over the long term, rising greenhouse gases are causing overall planetary heating equivalent to every person currently alive using about 17 electric kettles each to continuously boil the ocean - this would generate quite an energy bill and babies would probably need supervision!

 “During strong El Niño events, the warmer atmosphere can hold as much as 300 cubic kilometres more water (that’s 120 million Olympic swimming pools!) as invisible vapour. This helps to increase the heating power of El Niño further since water vapour is a potent natural greenhouse gas. In the long-term, warming due to rising greenhouse gas levels is adding more than 100 cubic kilometres of water to the atmosphere every decade, which also adds to the warming of climate.

 “There have been an unusual number of La Niñas in the first decade of the 2000s as well as a very lengthy one recently (late 2020 to early 2023) and this unusual pattern of warming affects changes in clouds and their effect in amplifying or dampening global warming. However, satellite observations and complex computer simulations show that the recent 2015/16 El Niño caused low-altitude clouds to melt away in the parts of the Pacific and this resulted in more sunlight reaching the surface, adding to the warming effect. It will be important to monitor the water cycle as well as global temperatures as the developing El Niño takes hold. It is more likely than not that the warmth of the next El Niño will cause global surface temperatures to breach the threshold of 1.5 degrees Celsius above pre-industrial times, perhaps in 2024. Breaching this limit for two decades or more is linked with a dangerous level of climate change which should be avoided as set out in the Paris climate agreement.”