Set aside for the moment the embarasingly emissions-hogging US, and consider the prospects for a greener China and India.
We now know the planet cannot support these countries at a US output level with US emissions.
They must grow much more green than America has. Or else.
Or, maybe not. It's not obvious that either country can afford it, for one thing.
And it's just possible they wouldn't need to if the US did (amid further outrage yesterday in Nairobi).
India must choose between getting rid of poverty or reducing emissions, says Surya P. Sethi, the principal energy policy advisor to the Indian government (via globalization and the environment).
Sethi has not doubt what that choice will be.
"I do not have the funds for both. My choice is to improve the lot of India's poor or reduce CO2 emissions so the developed world can breathe easier."
Sethi noted that India's estimated cost of carbon reduction goals is equivalent to its entire budget for poverty reduction.
Meanwhile, China confronts the worst of both worlds. It's economic growth has stunted its human development, as the costs of massively increased pollution show up in worsening health (via great red comet).
The degradation of China's environment is reaching a critical point where health and social stability are under threat, says Zhou Shengxian, China's top government official on the environment
Zhou noted that half the country's rivers were severely polluted and a third of its territory was damaged by acid rain.
"In some places, environmental problems have affected people's health and social stability, and damaged our international image."
Rapid industrialisation over the past two decades had transformed China into one of the world's most polluted countries, with local governments and industries shunning ecological protection in the pursuit of short-term gains.
In either case, it seems unlikely that China or India can afford the cleanup.
The question is: Can the US afford a cleanup? And, if so, will that be enough?