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You're right, it doesn't. But most of the books claims don't depend on a specific climate sensitivity. Climate Change is just one of the chapters. It also covers air pollution, deforestation, agriculture, biodiversity loss, ocean plastics and overfishing.

It combats the notion that we aren't achieving anything regarding long term sustainability because we're unable to coordinate on a global scale, by showcasing that we are not only moving in the right direction in many areas, we're also accelerating.

If Hansen is right and we live in a world with very high climate sensitivity then it's not looking good, but I'd still prefer to live in a world were we make noticeable progress and fall short, than in one were we watch the world turn into an uninhabitable ball of death while doing nothing.

>>Versio+(OP)
"Doing nothing" sounds like a straw man position. The question is rather whether optimism is warranted. I think there are some very worrying trends where we are not moving in the right direction at all, where it is even taboo to address the problem. I doubt she mentions those.