This year, dozens of bodies have been recovered from floodwaters in Australia as some of the worst floods in recent memory have occurred across New South Wales and Queensland.
Just two years ago, we had some of our worst bushfires, with 34 human deaths and an estimated three billion animals killed. I took this photograph at St Kilda Beach in January 2020, as smoke from these bushfires blanketed the city, creating eerily beautiful sunsets while Melbourne’s air quality temporarily became the worst on the planet. While it’s indisputable that climate change is making these events worse than they otherwise would be, I thought I’d put my degree in atmospheric science to use today, and explain some of the other drivers behind these events.
Australia’s climate is largely influenced by two important ‘oscillations’. The first is the El Niño Southern Oscillation (ENSO), and the second is the Indian Ocean Dipole (IOD). They relate to changes in temperature in the Pacific Ocean and Indian Ocean respectively, and both have warmer phases, neutral phases and colder phases. You may have heard of El Niño and La Niña, the warm and cold phases of ENSO, being referred to in weather forecasts.
Without going into crazy amounts of detail, both oscillations work like this: Changes in ocean temperature lead to changes in atmospheric pressure, changes in atmospheric pressure lead to changes in winds, and changes in winds lead to changes in temperature and rainfall. The result is that when ENSO is in its El Niño phase or the IOD is in its positive phase, Australia experiences hotter and drier weather – and vice versa.
The Black Saturday bushfires in 2009 occurred at the end of three consecutive positive IOD years (an event that has only happened once before since records began). In 2010/11, a combined La Niña and negative IOD led to devastating floods in Victoria and Queensland that claimed dozens of lives. The 2020 bushfires were the result of a strong positive IOD, and this year’s floods have come on the back of two consecutive La Niña years and a negative IOD.
Australia’s extreme weather events are always caused by strong phases of ENSO or the IOD (or both), and these extremes are further exacerbated by climate change, with increased global temperatures causing Australia to be drier in El Niño/positive IOD years, and wetter in La Niña/negative IOD years.
You can think of ENSO and the IOD as pendulums swinging between hot/dry and cold/wet at different and varying speeds. Every now and then they’ll line up together at the extreme hot/dry or cold/wet points, leading to particularly bad bushfires or floods respectively. Climate change is like humanity coming and putting some WD40 on the pendulums, allowing them both to move beyond their earlier extremes.
The Bureau of Meteorology accurately predicts both ENSO and the IOD months in advance, and of course we have been warned about the dangers of climate change for decades now. Australia’s bushfires and floods are only going to worsen in the years to come, and periods where ENSO and the IOD are both in their warmer or cooler phase together will be devastating.
Last year, a negative IOD was announced on July 20th, and La Niña was declared on November 23rd, with warnings beginning as early as September 14th. The deaths from this year’s floods are devastating, but especially so because they were entirely predictable.
The window of opportunity for preventing these kinds of events has long passed, but adaptation, preparation and long-term mitigation is still possible. How we adapt and prepare ourselves for these events is up to us, but it starts with electing governments that listen to climate scientists and take their warnings seriously.
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Bushfire Sunset, St Kilda Beach, Australia