As Australia’s climate changes, the study of compound events will become increasingly important.
They matter because as the consequences of carbon emissions play out via changes to Earth’s planetary systems, separate climate phenomena may converge.
Take the floods currently impacting New South Wales and Queensland.
Where it would be simple to assume high rainfall leads to a flooding event, climate extremes will potentially increase the frequency and severity of such hazards due to multiple environmental causes.
A follow-up La Niña event in 2022 again brought heavy rainfall across eastern Australia, but the already wet soils from previous rain and flooding events has likely amplified problem flooding.
In the future, rising ocean levels projected with increasing global temperatures will add another amplifier.
“A compound event is a natural disaster that’s caused by multiple hazards,” Dr Nina Ridder, a climate scientist at the Centre of Excellence for Climate Extremes (CLEX) at UNSW tells Cosmos.
“We see a lot with natural disasters that are caused by different hazards that they have a much higher impact.
“Some of the biggest disasters that we’ve seen over the past few years in Australia actually have multiple factors adding up together to cause devastating impacts: impacts we haven’t seen on record like the [Black Summer] bushfires and now floods in New South Wales.”
Ridder, about to start at large financial services provider Suncorp as a climate adviser, delivered the Penny Whetton Memorial Lecture at the annual Australian Meteorological and Oceanographic Society conference in Adelaide this week.
It’s perhaps appropriate that large insurers like Suncorp look to fill their ranks with climate experts.
The 2022 floods have caused $5.3billion in damage. Black Summer bushfires caused almost $2.5 billion in damage.
Opening her lecture with these figures helps quantify in people’s minds the physical damage caused by climate events that are now poised to become more frequent in a warmer world.
It’s also something that can cut through in a world saturated with climate information.
“[Those figures] catch people’s attention,” Ridder says.
“We’re doing science to reduce vulnerability, in my case, [the science] for the individual. Another thing is, also, if you open with damages, you get the attention of government.
“If we want to change something, if we want to raise awareness, if we want to spark a change in a system, we need to get attention first. And I think, unfortunately, our society runs on money.”
The study of compound events is a bit like being a doctor for climate
Climate experts like Ridder and her CLEX colleagues are effectively doctors for problems with the climate.
Like a GP, they assess a range of symptoms – events like floods or fires, storm surges, rising oceans – and try to diagnose their impacts.
A paper published by Ridder this year in the journal Weather and Climate Extremes uses specific models which perform “surprisingly well” at predicting increases in wet and windy, and hot and dry events in Australia.
The modelling anticipates Australia will find a significant shift towards increasing hot and dry events in future years, amplified by growing carbon concentrations in the atmosphere. Heatwaves and drought are expected to coincide, while northern Australia is likely to see increased risk of wind and rainfall extremes.
Ridder emphasises the predictive methods involved in climate analysis are not infallible, but do show plausible scenarios for the future.
She’s hopeful that increasing understanding of compound events in the scientific community will increasingly flow through to policymakers and the public.
“Starting from the impact and working our way up will be way more useful for the community, for Australia to prepare for future climate change,” she says.
“I’m really happy that people are starting to take notice [of compound events] and are interested in it.”
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