While pensioners on talkback debate the impact of a mooted carbon tax on their household budget, Julia Gillard wears out her shoe leather, and Tont Abbott sniffs another dead fish, another kind of carbon conference has been rolling out.

Over the past three days, Australian and international experts have gathered at Melbourne University to consider "Four degrees or more: Australia in a hot world".  In opening the conference, keynote speaker Professor Hans Joachim Schellnhuber, director of the Potsdam Institute, and former climate adviser to the German Chancellor and the EU, asked rhetorically: "What is the difference between two degrees (of temperature increase) and four degrees ?" His answer was concise. "The difference," he said, "is human civilisation".