When one in 10 year, one in 20 year, and one in 100 year floods occur multiple times in the same places in well under a decade it is obvious something has changed. And then, when so-called "rain bombs" deliver what have been described as one in 500 year and one in 1000 year floods, it is impossible to ignore what is happening up and down much of the eastern seaboard.

The floods, which have caused more than a dozen deaths, destroyed tens of thousands of homes, and forced hundreds of thousands of people to flee, are among the worst natural disasters in our history.

They have provoked a heroic response with ordinary Australians doing extraordinary things under the most challenging of circumstances. The "Dunkirk moments" in south eastern Queensland and on the north coast of NSW where locals used tinnies, inflatables, jet skis, canoes and almost anything that would float to rescue stranded neighbours were remarkable.

The courage and skill of the ADF crews who snatched victims from the jaws of death had to be seen to be believed. Credit is also due to the volunteers who rallied to feed and clothe the newly homeless and to join the "mud army" that is playing such an important role in the clean-up operation.

While the immediate challenge is to get through the crisis which saw 200,000 people under evacuation orders and another 300,000 on standby to evacuate in NSW on Thursday morning, it is important to put this, and the extreme weather that led to the "black summer" of 2019 and 2020, into context.

Neither should have come as a surprise. Ross Garnaut predicted a dangerous escalation in the bushfire risk as long ago as 2008. The Climate Council has been warning of extreme rainfall events for years.

It noted heavy downpours across south eastern Australia in the early 2010s were a clear indication climate change was intensifying extreme weather. It linked dangerous flooding in Victoria, NSW and Queensland to an atmosphere that was wetter and warmer as result of greenhouse emissions.

The latest floods coincided with the release of the sixth assessment report from the second working group of the Intergovernmental Panel on Climate Change. This document, which focussed on the damage climate change is already causing, could not have been more timely.

It devoted a chapter to Australia and delivered a scathing critique of the national response to the global warming challenge. The IPCC said that if the rest of the world adopted Australia's "steady as she goes" approach the earth would be heading towards catastrophic warming in excess of three degrees; far beyond anything it would be possible to adapt to.

A recent ACM survey of more than 7000 readers identified climate change as the most important single issue to voters in this year's federal election. The policies currently being espoused by both the LNP and the ALP just don't cut the mustard.

According to the Climate Council Australia should be aiming to reduce emissions below 75 per cent of 2005 levels by 2030 and to reach net zero by 2035. That is way beyond anything either Mr Morrison or Mr Albanese is willing to countenance on the grounds the cost would be prohibitive.

The trillion dollar question is whether or not the cost of doing much less is going to be even higher?

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