The scientific evidence is now overwhelming: climate change is a serious global threat and it demands an urgent global response.
Unless action is taken to reduce greenhouse gas emissions, global average temperature could rise by over 2°C and possibly as high as 5°C.
Such an increase "would be very dangerous indeed; it is equivalent to the change in average temperatures from the last Ice Age to today".
The scale of disruption "would be similar to those associated with the great wars and the economic depression of the first half of the 20th century".
The poorest countries on the planet will suffer earliest and most, even though they have contributed least to the causes of climate change.
The overall costs of climate change will be equivalent to losing at least 5 per cent and possibly as much as 20 per cent of global GDP every year.
The cost of taking action to reduce emissions to avoid the worst impacts of climate change could be as low as 1 per cent of global annual GDP.
Ultimately, stabilisation of greenhouse gases requires that annual emissions be brought down to more than 80 per cent below current levels.
Measures proposed include carbon pricing through taxation, emissions trading or regulation, and technology policy to drive the development of alternatives.
The benefits over time of actions to shift the world on to a the path of a "low-carbon economy" path could be as high as $2.5 trillion (€1.97 trillion) a year.