Tropical Cyclone Alfred is due to hit south-east Queensland about 1am on Friday morning, bringing the risk of destructive winds, extreme flooding and storm surges to millions of people around Brisbane, the Gold Coast and northern New South Wales.
After last year was recorded as the hottest on record around the world, and the hottest for Australia’s oceans, what role could the climate crisis be playing in Tropical Cyclone Alfred and its impacts?
What is climate change doing to cyclones?
Like all weather systems on the planet, tropical cyclones are forming in a world that is heating rapidly, mostly because of the burning of fossil fuels.
The planet – and the world’s oceans – are retaining more of the sun’s energy because of the extra greenhouse gases in the atmosphere.
But tropical cyclones are complex. They need ocean temperatures of at least 26.5C and the right setup of atmospheric conditions to form. In particular, they need low wind shear – that is, very little change in the wind, no matter how high they are blowing.
Studies have found that global heating is expanding the tropical belt – the region where cyclones can form – and other scientists have found that on average, the point at which cyclones achieve their maximum intensity has been shifting towards the poles.
Dr Savin Chand is an expert on tropical cyclones and climate change in the Australian region. “Climate change isn’t causing tropical cyclones to form because they have been forming for millennia, but the environment in which they’re forming is becoming more hostile [to their formation],” the associate professor at Federation University said.
“But when they do form, we know that sea surface temperatures that are their source of energy are much warmer now than they used to be.”
Chand has led research that has argued the number of tropical cyclones has fallen by 13% in the 20th century. This was in line with expectations from climate scientists that global heating could actually reduce the total number of cyclones that form – but, of those, there will be a shift to higher intensity systems.
“These sea surface temperatures and warming in the atmosphere provide fuel to the systems so, when they do form, they have more energy to feed on and this tends to make them more intense than they used to be,” said Chand.
How could climate change have affected Cyclone Alfred?
Cyclone Alfred formed in the Coral Sea towards the end of February when sea surface temperatures were almost 1C hotter than usual.
The same area of low pressure and rising air known as a monsoon trough that birthed Cyclone Alfred actually spawned two other cyclones, Rae and Seru, which moved east, while Alfred took a path south-east and off the Queensland coastline.
This year was the Coral Sea’s warmest summer on record.
Data from the Bureau of Meteorology shows ocean temperatures off Brisbane and to the south have been between 0.5C and 1C hotter than normal in recent days.
On Tuesday, Tropical Cyclone Alfred was far enough south to come into contact with a weather system common at lower latitudes – an area of high pressure – that grabbed Tropical Cyclone Alfred and pushed it west towards the south-east Queensland coastline.
On Wednesday, Cyclone Alfred was moving through this area as it approached the coast, where it was expected to cross on Friday morning as a category two system.
What is climate change doing to the impacts from cyclones?
There are three main impacts that scientists and authorities are concerned about from Tropical Cyclone Alfred’s move to the Queensland coast: damage from extreme winds, flooding from intense rain, and damage at the coast from storm surge and damaging waves.
A warmer atmosphere can hold more water that can fall as rain, and generally, the atmosphere can hold 7% more moisture for each 1C of warming. But rainfall intensities can be greater than this because, as raindrops form, they also release energy into a system.
Dr Andrew Dowdy, an associate professor and expert on tropical cyclones at the University of Melbourne, and his colleagues have advised that for Australia, infrastructure or building planners should consider that each degree of warming could increase rainfall by as much as 15%.
Dowdy points to several characteristics from climate change that can make the impacts from Cyclone Alfred worse. “Climate change has heated the oceans so the dice [are] loaded for a greater chance of hot water around Australia, like what we saw this summer,” he said.
“These hot ocean temperatures can help supercharge tropical cyclones with more extreme rainfall and flood risks.”
When ocean heat up from climate change, they expand, pushing up sea levels. The melting of ice attached to land like ice sheets and glaciers also raises sea levels.
Dowdy sea levels around the globe have already risen by 20cm due to climate change, “which can make damages worse when storms like Cyclone Alfred hit.”
“This includes more severe flood risks in tidal waterways like around the Gold Coast and the Brisbane River, as well as more severe coastal erosion.”
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