A child makes a snowman in Mt Macedon, Victoria
A child makes a snowman in Mt Macedon, Victoria

A bitter cold snap is bringing extremely cold weather to south-eastern Australia today, accompanied by low level snow in places like Canberra and Ballarat and storm force winds. So how unusual is this weather? Is it climate change or is it just winter? It’s a bit of both, so let’s discuss.

A fairly uncommon weather set up in the Southern Ocean is to blame, with low pressure systems stacked vertically on top of each other all the way from Antarctica up to Australia. Winds move in a clockwise direction around lows, so there’s a conveyor belt of icy southerly winds carrying polar air directly from Antarctica to us. Normally cold snaps are caused by south-westerly winds that have a bit of time to warm up before they get to Australia, but not so this time, which is why it’s so cold. Not only have temperatures been as much as 10 degrees below average today, but we’ve also seen snow down to low levels such as Melbourne’s and Hobart’s higher suburbs.

But before we scream “snowmageddon!” it’s worth noting that we actually saw snow down to even lower levels last winter. Extreme cold events like this are common during winter, as are heatwaves during summer. It’s the nature of the weather. Therefore, one can’t attribute any such single weather event to climate change because climate isn’t just about one single weather event; rather it refers to pattern of weather over at least a few decades.

There’s actually a bigger picture with this current event, too. What’s quite unusual at the moment is that while we have an Antarctic blast affecting southeastern Australia, meaning unseasonal tropical rain is falling over northern Australia, which is usually bone dry at this time of year. Jabiru in Kakadu National Park has already picked up 21.8mm in 24 hours, seven times what it would typically get during the entire month of July. But wait, there’s more. This tropical moisture across the Northern Territory is moving eastwards and intensifying, and it’s expected to clash with the cold Antarctic air from the south. This has the potential to causing record-breaking rain in parts of Queensland from Friday to Sunday. Flooding is possible, with the heaviest falls from about Bundaberg to Mackay.

So we have unusual cold weather and unusual tropical weather — both happening at the same time. Thus the real question is: are we seeing more such extremes in hot and cold weather in Australia? Yes we are, there is certainly a pattern emerging and this pattern is consistent with a warming atmosphere.