Over on Beware of the Train some people are discussing what the optimal philanthropic strategy is for people who want to do their bit to help the world as a whole, save people's lives, etc.

The two options under consideration are: (a) Mitigating Anthropogenic Global Warming and (b) working on the risk of artificial intelligence. To quote pozorvlak:

Last night I made a serious strategic error: I dared to suggest to some Less Wrongers that unFriendly transcendent AI was not the most pressing danger facing Humanity.

In particular, I made the following claims:

• That runaway anthropogenic climate change, while unlikely to cause Humanity's extinction, was very likely (with a probability of the order of 70%) to cause tens of millions of deaths through war, famine, pestilence, etc. in my expected lifetime (so before about 2060).
• That with a lower but still worryingly high probability (of the order of 10%) ACC could bring about the end of our current civilisation in the same time frame.
• That should our current civilisation end, it would be hard-to-impossible to bootstrap a new one from its ashes.
• That unFriendly AI, by contrast, has a much lower (