The speed of the changes we're seeing now - in terms of CO2 increase, ocean acidification, and global temperature rise - is unprecedented in the history of the human race.

Clearly, many species and whole ecosystems will struggle to cope as these shifts really take hold in the coming decades, undermining human economies, increasing the intensity and frequency of fires and floods, and likely leading to much more conflict and social breakdown than we have now.

The World Health Organisation estimates we already have 150,000 deaths a year due to climate impact, and a recent report by the Climate Vulnerable Forum, commissioned by 20 governments, puts the figure at 400,000.

Economically, the point of a carbon price is to shift the economy forward to a lower carbon basis in an efficient way.

This is as opposed to "direct action'', which attempts to reduce emissions at a cost of hundreds of dollars per tonne.

Smart thinking.