THERE is only one way to frame tomorrow’s carbon tax announcement: a start. Assume Australia hits its very soft target, cutting annual greenhouse gas emissions by 5per cent by 2020, and the rest of the world does everything they’ve promised: we are on course to suffer global warming of 4 degrees or more by the end of the century.

A conference in Melbourne next week featuring a who’s who of climate scientists will explore what warming of 4 degrees or more means, including for Australia. Apocalyptic is the only word for it, and understanding the implications is equally important for policymakers, business and the community. Keynote speaker Professor Hans Joachim Schellnhuber, director of the Potsdam Institute and climate adviser to the German Chancellor and to the EU, has said that in a 4-degree warmer world, the population “carrying capacity estimates [are] below 1billion people”.

Professor Kevin Anderson, director of the Tyndall Centre for Climate Change in Britain, was quoted in The Scotsman ahead of the 2009 Copenhagen conference saying the consequences were ‘‘terrifying’’.

‘‘For humanity it’s a matter of life or death ... we will not make all human beings extinct, as a few people with the right sort of resources may put themselves in the right parts of the world and survive. But I think it’s extremely unlikely that we wouldn’t have mass death at 4 degrees.

‘‘If you have got a population of 9 billion by 2050 and you hit 4 degrees, 5 degrees or 6 degrees, you might have half a billion people surviving.’’