Bali will be successful if countries do not walk away and if they can agree to negotiate for the next two years.
Failure is not an option. But success means the industrialised world meeting the developing world way beyond the halfway point.
These are the four steps they need to take during these talks.
They need to agree, according to the latest and best science to what extent greenhouse gas emissions need to be cut and by when. This should be a global cut of around 80% by 2050 with a peak no later than 2015.
Second, rich countries need to agree to take on legally binding emissions reduction targets which exceed the global goal; so at least 80% by 2050.
An index needs to be agreed that ranks all countries based on their responsibility for climate change (their emissions since, say, the Rio Earth Summit) and the extent to which they can afford to pay for cuts.
A new series of financial mechanisms need to be established to ensure that countries whose responsibility and capability is low receive finance to help them develop sustainably and cleanly.