Some tens of millions of people will probably die as a result, or some hundreds of millions if we are really unlucky, but there is still time to avoid the worst. And anyway, it can not be helped: this is the way we do business.
An example: President Barack Obama has hired the best people in the business as his climate advisers. They know exactly how grave the situation is, and so does Mr Obama. Yet when his chief scientific adviser, John Holdren, was asked why the US would not commit to the same target for greenhouse gas emissions by 2020 as the European Union, he replied as follows.
"If we had not wasted the last eight years, we could probably achieve that target. But we did waste the last eight years and in consequence, it does not make a lot of sense for us to officially embrace a target that is not realistically within reach."
Analyse that sentence, and what it says is: We did not do what we should have for the past eight years, so we can not do what we should for the next 12 years either.
Get upset about it if you like, but this is how the system works. Mr Obama cannot ignore the fact that climate change denial is still stronger in the United States than anywhere else, and that much of the US Congress is a wholly owned subsidiary of the fossil fuel industries.
He is going as far as he can, for now. He can not go any further even if what he is doing is not good enough, which it is not.
All the parts of the system work like that, not just the American parts. The Indian government, for example, cannot ignore the resentment felt by most Indians when their country is asked to cut its greenhouse gas emissions and slow its own development to deal with a problem that India had little role in creating.
Almost all the excess greenhouse gas that is in the air now was put there by the old industrialised countries, yet the newly industrialising ones like India will be hurt first and worst by the resulting climate change.
Cutting their emissions means slowing their escape from poverty, which the old rich countries were never required to do - and if they refuse, climate change will hurt them even faster and worse. No matter which way they jump, India's decision-makers will face the anger of the voters.
Every country comes to the table with powerful lobbies at home to satisfy, and its something of a miracle that the 18 biggest emitters, countries that together account for 80% of human greenhouse gas emissions, all managed to agree that the average global temperature should never be allowed to rise more than 2deC (3.4degF) above the 1900 level. But there were other important things that they did not agree on.
The big industrialised countries of the G8 (US, Russia, Japan, Germany, Britain, France, Italy and Canada) said they would cut their emissions by 80%, and asked the developing countries to cut their emissions enough to produce 50% global cuts by the same date. The developing countries refused.
But those same rapidly industrialising countries of the G5 (China, India, Brazil, Mexico and South Africa) then called the rich countries' bluff by demanding that the G8 set an interim target for emissions cuts by 2020.
Any leader can make promises for 2050, safe in the knowledge that they will not be around by then. Promises for 2020, on the other hand, may fall due while you are still in the game - so the G8 leaders refused.
Nevertheless, the idea that all these countries, plus five other big emitters (the European Union, Indonesia, Egypt, South Korea and Australia) would actually agree in mid-2009 on a never-exceed target of +2deC would have been seen as fantasy only 18 months ago.
"It certainly doesn't give you a roadmap on how you should get there, but at least they've defined the destination," said Rajendra K. Pachauri, the chair of the Intergovernmental Panel on Climate Change.
Well, not quite, because even at only 2degC hotter, the world would be running out of food (global warming hits food production very badly), and that would lead to waves of refugees, failed states, and savage local wars over the remaining water, especially in the sub-tropical regions.
Moreover, the 2deg target gives us only a 50% chance of avoiding tipping points that would lead to runaway warming.
So we ought to have much more ambitious targets now, and strict penalties for those countries that miss or evade them. Our children's future really does depend on it. But we cannot have stricter targets yet, because the international political system does not work that fast - and we have no time to re-design it.
If we are lucky, some early disasters that do not kill too many people will frighten the world's countries into accepting tougher cuts in emissions while there is still time to avoid the worst, but this is the best that we are going to get for now.
So two cheers for the 2deg limit.
- Gwynne Dyer is an independent London journalist.
