Are Southern Hemisphere 'Polar Blasts' caused by global warming?
Looking at the southern hemisphere polar jet, there is a large trough (meander) in the jet stream bringing cold air a long way north from the Antarctic to south eastern Australia at present. The relevance of the position and shape of the jet stream is thought to be important for keeping cold polar air in place above the antarctic/arctic, with a strong jet stream keeping cold air hemmed in above the poles while a weak jet stream meanders allowing cold waves/blasts to escape into the midlatitudes. This previous Stack Exchange question sets out how the theory of arctic/polar amplification which is thought to affect the position and shape of the jet stream is being studied in connection to climate change (Generally it has been proposed that global warming will make the jet stream more wobbly/meandering, and so increase instances of cold weather in the mid latitudes).

Single weather events such as this are not caused by global warming, but it has been hypothesised that their frequency of occurrence may change due to warming, though as you can read in the linked stack exchange this theory is not universally accepted.