An homage to the scientist who produced the first big-picture view of the Southern Hemisphere's atmosphere reveals climate complexities long overlooked.
In the early 1970s, scientist Harry van Loon pulled together scattered island weather logs and the few radiosonde balloon measurements available to complete the first big picture overview of Southern Hemisphere weather.
His book, Meteorology of the Southern Hemisphere, written with Chester Newton, was limited by the thin data record available yet stood as the first real effort to address a longstanding blind spot in atmospheric science.
Roughly 81% of the Southern Hemisphere is ocean, compared with 61% in the north, creating climate systems that behave differently from their northern counterparts.
Understanding these vast ocean-atmosphere systems, which shape rain, temperature and wind, is central to grasping how the global climate machine operates.
It also helps people in the Southern Hemisphere gauge practical risks, from how much food they can grow to how safe their homes are from floods or fires.
Yet textbooks, modelling schemes and observational networks remain skewed towards the Northern Hemisphere, where most long-term records, funding and population sit.
A second edition of Meteorology of the Southern Hemisphere, edited by David Karoly and Dayton Vincent, wasn't published until 1998.
Scientists had, by then, discovered giant, powerful weather systems that weren't even mentioned in the first book, drawing on new data from the satellites and ocean buoys now covering great swathes of the Southern Hemisphere.
Now, a new monograph details a far more intricate and interconnected picture of the Southern Hemisphere's short-term weather forecast, but the giant, long-term climate systems set to shape the region's future.
The 550-page monograph, Meteorology and Climate of the Southern Hemisphere , written by more than 100 researchers from 22 countries, now offers the most complete account yet of the hemisphere's weather and climate, from the tropics to the Antarctic Plateau.
UNSW climate scientist Associate Professor Andrea Taschetto , one of three editors, says the update includes advances in understanding extreme events, including east-coast lows, heatwaves and atmospheric rivers - long, narrow corridors that transport vast volumes of water vapour.
When these atmospheric rivers reach Antarctica, they can trigger widespread melt; when they hit Australia or South America, they can deliver destructive rainfall.
The new book also covers systems that can drive extreme weather and heighten bushfire risk, including the Southern Annular Mode - which shifts storm tracks and high-latitude winds - and Sudden Stratospheric Warming, a rare polar event in which temperatures high above Antarctica can climb almost 20°C within days.
El Niño and La Niña's shifting guises
The past 25 years have also reshaped scientific understanding of the large-scale patterns that drive global weather - notably the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), which underpin Australia's drought-and-flood cycle.
"People often assume an El Niño guarantees a dry year, but that relationship doesn't hold," A/Prof. Taschetto says.
"ENSO doesn't operate as a single pattern. El Niño and La Niña come in different shapes and strengths, and those differences produce distinct rainfall outcomes."
ENSO also interacts with the Southern Annular Mode and the IOD. Their overlapping phases can amplify or mute each other, complicating seasonal forecasts.
Recent ocean trends present another challenge: the western Pacific has warmed faster than the east, whereas many models project more uniform warming.
"That discrepancy matters because the background state - the long-term temperature pattern - shapes how ENSO evolves," she says. "Natural variability may explain it, but scientifically it's important and can't be ignored."
Researchers are now pairing increasingly advanced models to determine whether the observed pattern is a temporary fluctuation or evidence of missing processes in current simulations.
"We'll always have uncertainties. That's true of every field that works with future scenarios. But we're developing a better understanding of what's plausible," A/Prof. Taschetto says.
We'll always have uncertainties. That's true of every field that works with future scenarios. But we're developing a better understanding of what's plausible.
The long-term outlook for Australia, she says, is unambiguous: warming will intensify extreme events, and southern Australia is projected to become drier.
"ENSO sits on top of that overall trend, adding year-to-year swings that matter enormously for agriculture and water."
A southern correction to a northern tilt
Associate Professor Thando Ndarana , a meteorologist at the University of Pretoria and a co-editor, says that, for the first time, most of the work comes from researchers living in the Southern Hemisphere.
"We know the weather and climate locally better than anyone else. If scientists in a region are not leading that work, then they're not being responsible for what needs to happen there."
That lived experience, he says, shapes research priorities. One example, he says, is South Africa's catastrophic April 2022 floods - which killed hundreds and caused tens of billions of rand in damage.
A/Prof. Ndarana says that event traces back to a chain of atmospheric processes that spanned the South Pacific, South America and the South Atlantic before reaching the South African coast.
Modern early-warning systems, he says, depend on modelling that captures those long-range dynamics.
A UN report found that countries with robust early-warning systems have disaster death rates about eight times lower than countries with only limited warning systems.
"Better understanding of atmospheric dynamics leads to better forecasts and stronger early-warning systems - and that saves lives," A/Prof. Ndarana says.
A community built on collaboration
He says working on the book was also personally rewarding.
"I didn't know Tercio Ambrizzi or Andrea, the other two editors, before starting this project but we've since become really close - as peers and as friends."
A/Prof. Taschetto says the project's collaborative spirit was part of its strength.
"Researchers at every career stage and from so many countries in the south came together. That shared purpose is what drives the science forward."
Researchers at every career stage and from so many countries in the south came together. That shared purpose is what drives the science forward.
The work, she says, also pays tribute to the "heroic" efforts behind the first edition.
"When van Loon and his colleagues wrote in the late 1960s, observations south of 30° were scarce. That they produced a hemispheric overview at all was a scientific feat."
The new work is dedicated to van Loon, who wrote five of the original monograph's nine chapters.
Born in Denmark in 1925, van Loon joined the resistance during the Nazi occupation.
After the war he discovered meteorology, worked at the Danish Weather Bureau and later joined major US research institutions.
During the '50s, he served as a weather forecaster in Antarctica, which helped support aviation during one of the era's largest scientific expeditions. A glacier on the continent now bears his name.
He published his final paper at 91. He died in 2021, at 96.
A/Prof. Taschetto says the new book builds on this legacy.
"It's a resource for researchers and postgraduate students, but it's also a marker of how far the field has come.
"We now have the data and the expertise in the south to understand our own climate system in new ways.
"The science has moved on, but it still relies on people helping each other and sharing their knowledge and time.
"This version was made possible by so many people, including David Karoly, who acted as a mentor for the book, generously sharing his experience editing the previous version."
