Following three consecutive La Niña years of above-average rainfall, Australia could swing to one of the hottest El Niño periods in 2023 on record. This “shift from one extreme to the other” could bring “record-challenging heat” to Australia, reports Sky News Australia.
The latest Bureau of Meteorology climate models show an increasing likelihood that La Niña will end this year. Scientists say predictions will be more accurate following April’s “autumn predictability gap” – when the Pacific enters a reset mode. However, following three consecutive La Niña years, the ocean is set for a switch. “The Pacific must be quite charged with heat ready to have an El Niño”, Cai Wenju, a senior CSIRO climate scientist, told Guardian Australia. “I wouldn’t be surprised if we had an El Niño by the end of the year.”
La Niña has a relative cooling effect on average global temperatures. Despite this, the last three years of La Niña have been some of the hottest on record. Periods of El Niño typically raise global average temperatures by 0.2°C. Therefore, a shift to an El Niño this year could mean the world breaches 1.5°C of warming above pre-industrial levels for the first time in 2024, according to the UK Met Office.
Climate change is supercharging weather extremes
El Niño and La Niña have perhaps the most influence on year-to-year climate variability in Australia, explains Australia’s Bureau of Meteorology. They are a part of a natural cycle of sustained periods of warming or cooling in the Pacific Ocean. This is the El Niño–Southern Oscillation (ENSO) cycle, which operates over timescales from one to eight years.
While the ENSO cycle is a natural phenomenon, human-produced greenhouse gas (GHG) emissions from burning fossil fuels are heating the planet and making extreme climate events more frequent and intense. “Extreme El Niño and La Niña events may increase in frequency from about one every 20 years to one every 10 years by the end of the 21st century under aggressive greenhouse gas emission scenarios”, said Michael McPhaden, Senior Scientist at the National Oceanic and Atmospheric Administration (NOAA). “The strongest events may also become even stronger than they are today.”
El Niño and La Niña: Impacts for Australia
Australia is already suffering the effects of more frequent and extreme weather events due to climate change. The country is enduring three straight years of above-average national rainfall, with many regions experiencing record-breaking annual rainfall. The resulting severe flooding cost the economy AUD $5 billion last year alone, with a further AUD $3.5 billion spent on disaster recovery payments. Treasurer Jim Chalmers has warned economic pressure from climatic disasters will continue through 2023.
Should this year swing to El Niño, these wetter conditions could switch to hotter, dryer conditions bringing bushfires and drought.
Already, Australia’s climate has warmed by around 1.47°C in the period 1910–2021, the Australian Bureau of Meteorology has confirmed. Furthermore, scientists predict the country’s average temperature will continue to rise unless the world’s big polluters drastically abate their greenhouse gas (GHG) emissions. This hotter climate will also increase the frequency and intensity of extreme weather events across Australia.
Due to such projections, researchers warn more than 2,400 lives will be lost to bushfires in Australia in the decade to 2030. This is along with profound physical and mental health impacts for many more, according to modelling led by Monash University. The cost to the economy over the period would be AUD $17.2 billion. “Even based on conservative assumptions, the health and economic burden of bushfires in Australia looms large”, the paper concluded.
What causes El Niño and La Niña?
El Niño occurs when water surface temperatures in the central and eastern tropical Pacific become significantly warmer than average. This causes a shift in atmospheric circulation. Generally, the equatorial trade winds blow east to west across the Pacific. El Niño events are associated with a weakening or reversal of these winds.
For Australia, El Niño typically leads to hotter temperatures, reduced rainfall, fewer tropical cyclones, later monsoon onset and increased fire danger in southeast Australia.
La Niña occurs when equatorial trade winds become stronger. This changes ocean surface currents and draws up the cooler deep water from below, resulting in a cooling of the central and eastern tropical Pacific. These stronger winds also contribute to warmer surface waters to the north of Australia. The warming of ocean temperatures in the western Pacific primes the area for rising air, cloud development and rainfall.
La Niña typically means cooler daytime temperatures (south of the tropics), warmer overnight temperatures (in the north), increased rainfall and flooding, greater tropical cyclone numbers and earlier monsoon onset.