November 30, 2023
Record summer expected to hit the southern hemisphere

Record summer expected to hit the southern hemisphere

A sugar cane field is set ablaze in a controlled burn at Home Hill, Burdekin Shire, Australia.

A similar combination of weather patterns in 2019-2020 resulted in the devastating “black summer” bushfires in Australia.Credit: Carla Gottgens/Bloomberg via Getty

The Southern Hemisphere faces a summer of extremes, scientists say, as climate change amplifies the effects of natural climate variability. This follows a northern hemisphere summer that saw extreme heatwaves across Europe, China and North America, setting new records for day and night temperatures in some areas.

Andrew King, a climate scientist at the University of Melbourne in Australia, says there is “a high probability that we will see record temperatures, at least on the global average, and that we will see some particularly extreme events in some parts of the world”.

Effects of El Niño

As 2023 draws to a close, meteorologists and climate scientists are predicting weather patterns that will lead to record land and sea surface temperatures. These include a strong El Niño in the Pacific Ocean and a positive Dipole in the Indian Ocean.

“These kinds of big factors can have a big influence on drought and extremes across the southern hemisphere,” says Ailie Gallant, a climate scientist at Monash University in Melbourne, Australia, and chief investigator at the Council’s Center of Excellence for Climate Extremes. Australian Research. . In Australia, both phenomena tend to “cause significant drought conditions, especially in the east of the country”.

During 2019 and 2020, the same combination of climate factors contributed to bushfires that burned for several months across more than 24 million hectares in eastern and southeastern Australia.

In East Africa, the combination of El Niño and a positive Indian Ocean Dipole is associated with wetter than normal conditions and a greater likelihood of extreme rainfall and flooding. Above-average rainfall is expected for much of southern Africa in mid to late spring (October to December), followed by hot and dry conditions in summer.

A man carries an elderly man across a flooded road during heavy floods in the village of Sir Lowry, South Africa.

South Africa suffered floods in the spring of 2023.Credit: Rodger Bosch/AFP via Getty

In South America, El Niño has a more checkered effect. It brings wet conditions and flooding to some parts of the continent, particularly Peru and Ecuador, but hot and dry conditions to the Amazon and regions of the Northeast.

Before 2023, three consecutive years of El Niño’s counterpart, La Niña, brought relatively cool and wet conditions to eastern Australia and led to record droughts and hot weather in the lower half of South America. But the “triple dip” La Niña helped mask global temperature increases associated with rising greenhouse gas emissions and climate change, King says.

He says that along with El Niño conditions, the full effect of climate change is “properly emerging.”

Meanwhile, human activity continues to contribute to greenhouse gas levels in the atmosphere.

Climate scientist Danielle Verdon-Kidd of the University of Newcastle, Australia, says heatwaves — one of the deadliest weather events — are a major concern for the summer of 2023. “We know that the conditions we have now… This type of system is more likely to develop during the summer,” she says

The summer of 2023 in the northern hemisphere saw unprecedented high temperatures in China, parts of Europe and North Africa, the worst forest fire season ever recorded in Canada and severe marine heat waves in the Mediterranean. Large landmasses in the Northern Hemisphere create areas of hot, dry air circulation, known as heat domes, that block low pressure systems that would otherwise bring cooler, wetter conditions.

In the Southern Hemisphere, heat domes are less of a concern. “We also have a large landmass in Australia,” says Verdon-Kidd, but the southern hemisphere has a much higher ocean-to-land ratio, “so our systems are different.”

In addition to these converging phenomena, the Sun and atmospheric water vapor will influence the climate. King says the Sun is approaching the peak of its 11-year activity cycle, which could contribute to a small but significant increase in global temperatures. Meanwhile, the eruption of the Hunga Tonga – Hunga Ha’apai underwater volcano in January 2022 has increased the amount of water vapor in the upper atmosphere, which is also expected to slightly increase global temperatures. Temperature changes are “hundredths of a degree from the global average, so they’re not nearly as important as climate change or even El Niño right now, but they’re a small factor,” says King.

Planet warming.  Graph showing the increase in global average temperature since 1970.

Source: Central Climate

Warm oceans

The oceans are also feeling the heat. Global average sea surface temperatures reached a record high in July this year, and some areas were more than 3°C warmer than usual. There were also record levels of sea ice around Antarctica during the winter, which could lead to a feedback loop, says Ariaan Purich, a climate scientist at Monash University. “Large areas of the Southern Ocean that would normally still be covered by sea ice in October are not,” she says. Instead of being reflected off the white ice, incoming sunlight is more likely to be absorbed by the ocean’s dark surface. “That warms the surface and melts more sea ice, so we can have that positive feedback.”

Melting icebergs are seen on Horseshoe Island in Antarctica.

As Antarctica’s ice melts, the darker water absorbs more sunlight, triggering more melting.Credit: Sebnem Coskun/Anadolu Agency via Getty

Another meteorological element present this summer is the Southern Annular Mode, also known as the Antarctic Oscillation, which describes the shift to the north or south of the belt of westerly winds that surrounds Antarctica.

In 2019, the Southern Annular Modality was in a strongly negative phase. “What this meant was that across eastern Australia there were a lot of very hot, dry winds blowing from the desert into eastern Australia, which really exacerbated the risk of bushfires,” says Purich. A positive Southern Annular Mode is associated with increased precipitation over most of Australia and southern Africa, but with dry conditions in South America, New Zealand and Tasmania.

The South Annular Mode is currently in a positive state, but is forecast to return to a neutral position in the coming days, and “I would say we don’t expect to have a very strong negative South Annular Mode this spring,” says Purich. .

And no matter how hot the summer is, the worst may be yet to come. Atmospheric scientist David Karoly of the University of Melbourne, who was a member of the Intergovernmental Panel on Climate Change, says the biggest impact of El Niño will likely be felt in the summer of 2024–25. “We know that the impact on temperatures associated with El Niño happens one year after the event,” says Karoly.

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