Human extinction within 100 years?

I think Peter Barrett underestimates our chances. While climate change threatens to make life exceedingly uncomfortable for a large part of humanity, and cause famine, the spread of disease, and even war, it does not pose a threat to the survival of humanity as a species. I don't think it even poses a threat to the survival of humanity as a technological civilization - though it may alter the nature and extent of that civilisation. We and our infrastructure are distributed enough to survive a major asteroid strike; we can endure climate change even at its worst.

This does not mean that climate change should be ignored. The threats it does pose justify taking strong action against it. But we should be clear about what those threats are, and avoid inflating them to ridiculous levels. By doing the latter, peter Barrett has done those fighting for action on climate change no favours whatsoever.