Record heat is set to reach the Southern Hemisphere with the start of summer

Scientists say the Southern Hemisphere is facing an extreme summer, as climate change amplifies the effects of natural climate fluctuations. This comes on the heels of a Northern Hemisphere summer that saw extreme heatwaves across Europe, China and North America, setting new records for daytime and nighttime temperatures in some regions.

Andrew King, a climate scientist at the University of Melbourne in Australia, says there is a “high chance of seeing record high temperatures, at least on the global average, and seeing 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 send land and sea surface temperatures to record levels. These include a strong El Niño in the Pacific Ocean, and a positive dipole in the Indian Ocean.

“These types of large drivers can have a significant impact on drought and extreme events in the Southern Hemisphere,” says Ellie Gallant, a climate scientist at Monash University in Melbourne, Australia, and a senior researcher at the Australian Research Council Center of Excellence for Climate Extremes. . In Australia, these two phenomena tend to “cause significant drought conditions, especially across the east of the country.”

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

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

In South America, El Niño has a more volatile effect. It brings wet and flooded conditions to some parts of the continent, especially Peru and Ecuador, but brings hot and dry conditions to the Amazon and northeastern regions.

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

Combined with El Niño conditions, he says, the full impact of climate change is “right on display.”

At the same time, human activity continues to contribute to levels of greenhouse gases in the atmosphere.

The average global temperature in 2023 is now likely to reach 1.5 degrees Celsius

Heatwaves — one of the deadliest weather events — are a major concern for the summer of 2023, says climate scientist Danielle Verdon Kidd of Newcastle University in Australia. “We know that the conditions we have now… make it more likely that they will develop,” she says. “These types of systems during the summer.”

The Northern Hemisphere summer of 2023 saw unprecedented temperatures in China, parts of Europe and North Africa, the worst wildfire season on record in Canada, and extreme marine heatwaves in the Mediterranean. Large land masses in the Northern Hemisphere create areas of warm, dry, diffuse air known as heat domes, which block low-pressure systems that would bring cooler, wetter conditions.

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

In addition to these converging phenomena, the sun and water vapor in the atmosphere will affect the weather. The sun is approaching the peak of its 11-year cycle of activity, which may contribute to a small but significant increase in global temperatures, King says. Meanwhile, the eruption of the Honga Tonga-Hunga Haapai underwater volcano in January 2022 increased the amount of water vapor in the upper atmosphere, which is also expected to lead to a slight increase in global temperatures. The temperature changes are “hundredths of a degree compared to the global average, so it’s not anywhere near as important as climate change or even El Niño right now, but it’s a small factor,” King says.

Hot oceans

The oceans also feel the heat. Global average sea surface temperatures reached a record high in July this year, and some areas were more than 3 degrees Celsius warmer than normal. There were also record low levels of sea ice around Antarctica during the winter, which could trigger a feedback loop, says Ariane Burich, a climate scientist at Monash University. “Large areas of the Southern Ocean that would normally remain covered in sea ice in October are not,” she says. Instead of incoming sunlight being reflected off the white ice, it is more likely to be absorbed by the dark ocean surface. “This makes the surface warmer and will melt more sea ice so we can get this positive feedback.”

Another meteorological element this summer is the southern annular mode, also known as the Antarctic Oscillation, which describes a northward or southward shift of the belt of westerly winds that orbits Antarctica.

In 2019, the southern annular situation was going through a strong negative phase. “What this means is that across eastern Australia, there have been a lot of very hot, dry winds blowing from the Sahara into eastern Australia, which has really exacerbated the bushfire risk,” Burisch says. A positive southern annular mode is associated with increased rainfall over much of Australia and South Africa, but is associated with dry conditions in South America, New Zealand and Tasmania.

The southern annular situation is currently in a positive state, but is expected to return to neutral in the coming days. “I would say that we do not expect to have a very strong negative southern annular situation this spring,” Buric says. .

Although the summer may be hot, the worst is yet to come. Atmospheric scientist David Karolyi of the University of Melbourne, who was a member of the Intergovernmental Panel on Climate Change, says the greatest impact of El Niño is likely to be felt in the summer of 2024-2025. “We know that the effect on temperatures associated with El Niño occurs in the year following the event,” Karolyi says.