Australia never had a "catastrophic" fire danger rating until 2009. It was introduced in the wake of the then unprecedented Black Saturday bushfires in Victoria. Catastrophic conditions were forecast for the first time in Greater Sydney last month – on November 12 to be exact.

On Thursday, a little over a month later, while parts of Australia experienced record heatwaves into the 40s celsius, catastrophic conditions were forecast for Greater Sydney yet again, coupled with extreme heat for the entire state. The NSW Premier declared a state of emergency for the next seven days, including Christmas Day.

Connecting the dots ... the carbon we burn makes it hotter, and exposes us to more fire. Credit:Nick Moir

This is the second time a catastrophic bushfire danger rating has been declared over such a densely populated area, covering almost 5 million residents across eastern NSW. In catastrophic conditions, fires cannot safely be fought. Homes are not built to withstand fires in these conditions, and lives can be lost.

Already, it is estimated that more than 2.9 million hectares has been burnt in NSW and Queensland, with 2.7 million of that in NSW, where its perimeter runs to more than 19,235 kilometres. That's almost the equivalent of three return trips between Sydney and Perth.