Forget a 1 or 2-degree increase. Due to chronic political failure, we're looking at 4 degrees.
NO DOUBT Australia's chief climate change adviser, Ross Garnaut, ''gets'' the urgency of the climate debate, but will the politicians listen this time, and what if the whole debate is still in the wrong ballpark?
In the first update to his 2008 Climate Change Review on Thursday, Professor Garnaut was clear about the link between recent extreme weather events - from Black Saturday to cyclone Yasi - and global warming.
What's more, he flagged that since his 2008 review, the science has only become more alarming.
With warming now at less than 1 degree above pre-industrial levels, and with the sort of emissions growth coming from the industrialisation of China, India, Indonesia and other developing countries, ''if we are seeing an intensification of extreme weather events now … you ain't seen nothing yet''.
A key argument in Garnaut's update is that although the costs of adapting to climate change are rising fast, ''there is no point in time at which it is wise to conclude that the damage already caused from climate change is so large that any subsequent damage is of minor importance''.
And, he writes, the costs rise significantly as warming rises from 1 to 2 degrees or more. ''The challenges and costs of climate change associated with an additional degree of warming, regardless of the warming the planet has already experienced, is likely to overwhelm any attempts at adaptation to reduce the costs.''
But Garnaut is stuck with the political reality in Australia, the proud ''world champions'' of greenhouse pollution per head - ''by a wide margin''.
The 2008 review recommended we cut our greenhouse gas emissions by 25 per cent by 2020 if the rest of the world moved ambitiously to limit warming - roughly, to 2 degrees, the goal in the Copenhagen Accord.
Our government is a long way short of accepting a 25 per cent emissions target, never mind the opposition.
But according to the Climate Tracker website, even if every country implemented its maximum pledge, the world faces warming of 3 to 4 degrees by the end of this century.
What does that mean? In a coming paper, David Spratt, author ofClimate Code Red, pulls together recent scientific work and warns that atmospheric carbon dioxide concentrations should not be allowed to exceed 350 parts per million (they are 400 ppm now).
While much policy discussion is about limiting warming to 2 degrees, Spratt writes, the scientists are telling us it should be kept to under 1 degree, and the planet is actually heading towards 4 degrees due to ''chronic political failure''.
The implications of 4 degrees will be canvassed at a Melbourne conference in July. Spratt writes that the subject ''cannot be discussed politely''.
Such a hot world would be:
■ ''Warmer than during any part of the period in which modern humans evolved.''
■ ''Half of the world would be uninhabitable.''
■ ''3C may be the 'tipping point' where global warming triggers events that produce more warming, leaving us powerless to intervene.''
Spratt cites work by Professor Kevin Anderson, director of Britain's Tyndall Centre for Climate Change.
Anderson argues previous large-scale exercises in decarbonisation - Britain's 'dash for gas', France's nuclear switch - achieved negligible emissions reductions.
The impact of economic downturns - after 9-11, and the GFC - was far more substantial.
He concludes that ''dangerous climate change can only be avoided if economic growth is exchanged, at least temporarily, for a period of planned austerity within (developed) nations and a rapid transition away from fossil-fuelled development within (developing) nations.''
That's the ballpark.