Why are greenhouse gasses such an important issue in Australia?

No, really.  Granting that anthropogenic global warming is a very important, serious problem . . . why is reducing Australia's emissions a major issue in Australian politics?  Australia emitted 1.28% of the world's carbon dioxide in 2007.  Estimates I see are Australian methane and other emissions are equivalent to about half the warming effect of their CO₂, so making the impact-maximizing assumption there are no other greenhouse gasses than carbon dioxide emitted by anyone else anywhere, Australia is responsible for about 2% of global greenhouse emissions, which share is declining as the developing world industrializes.

If Australia's emissions magically went to zero, it would have no discernible impact whatsoever on global warming.  The science says there is nothing Australia can do about global warming on its own that will have any effect.  So why is Australia even considering expensive, unilateral cuts in emissions that won't do anything to actually prevent global warming?