Early last week, the BoM declared that El Niño had arrived. As described in this article, during an El Niño Australia typically experiences warmer temperatures, drier conditions, an increase in fire weather and a decrease in cyclone activity. However, given that El Niño is a large-scale climatic factor, a single El Niño event has global implications.  

The changes in the Pacific Ocean surface temperature and density have impacts on the atmospheric circulation of the world through ocean-land-air connections called teleconnections. These result in repetitive patterns of warming/cooling, drier/wetter conditions, and increased/decreased chances of certain extreme weather events over all continents. When the Pacific Ocean exhibits El Niño conditions we see: 

Heating: 

El Niño is known to increase the global annual temperature by an average of 0.2 degrees. However, just because the annual average temperature increases during these events, it doesn’t mean that all locations around the global warm in an El Niño. Other than Australia, southern & eastern Asia and Africa also experience higher than average temperatures during an El Niño. In addition, El Niño generally pushes warm air to the south via a westerly air jet, resulting in a warmer than average winter in North America and western Canada, and a cooler than average winter in eastern Canada and Europe. While in summer, El Niño acts to enhance temperature differences leading to warmer than average temperatures in Europe and North America. 

Fig. 1) (Right) Plot of the average surface temperature anomalies worldwide during the southern Hemisphere summer during El Niño years. (Left) Plot of the average surface temperature anomalies worldwide during the southern Hemisphere winter during El Niño years. (Plots from NOAA, 2023)

Rainfall: 

The change in the strength/direction of the easterly tropical winds during El Niño lead to shifts in common seasonal rainfall patterns, particularly in the tropics. Australia, southeast Asia, the Pacific Islands, southern Africa, the Sahara, India, the Amazon, as well as some of the more northern areas of North America experience dry conditions and an increase in potential droughts, whilst Central America, eastern South America, northern Argentina, western Asia, south India and the Horn of Africa all experience wetter than average rainfall and an increase in flood potential. 

Fig. 2) (Right) Plot of the average rainfall anomalies worldwide during the southern Hemisphere summer during El Niño years. (Left) Plot of the average rainfall anomalies worldwide during the southern Hemisphere winter during El Niño years. (Plots from NOAA, 2023)

Generally speaking, El Niño results in greater socioeconomic impacts than La Niña worldwide, despite La Niña’s ability to produce extreme weather. This is due to a number of factors: 

1. La Niña is the name given to conditions characterised as “enhanced normal conditions”, whilst El Niño describes conditions opposite to normal conditions. Thus, extreme weather is more common during an El Niño. 
2. Stronger El Niño events are statistically more frequent than strong La Niña events, and when the event is stronger, the resultant impacts are also stronger. 
3. The formation of an El Niño event is less predictable than the formation of a La Niña event, making it harder to prepare for its impacts in advance. 

Despite all the above, what is known is that El Niño events do not linger for long, and generally last over the time span of months. So, despite the expected heat looming this Australian summer, we can take solace in the fact that next summer should not be as hot.