In reply to stp:
> A couple of ways spring to mind. An all out nuclear war would be pretty damaging,
Nowhere near enough to kill all life. I don't think the current arsenal and resultant short term "nuclear winter" could even kill all the humans unless you rounded them all up at the ground zeros first.
> possibly triggered by the energy crisis.
Have you looked at the falls in price per kW of solar over the last decade? One of the great successes of environmental lobbying groups. It's still falling.
> Secondly, run away climate change. The most pessimistic forecasts suggest ending up with a climate somewhat like Venus,
If you have a forecast like that from actual scientists I'd be keen to see it. For starters I'd love to know where the extra 89 atmospheres worth of gas will come from.... Tosh.
> not a place where scientists believe life could exist.
Speak for yourself. We are only just starting to understand extermophile life on earth and in near earth orbit. Hydrothermal vents are similar in many ways to Venus in terms of extremes. Venus is more extreme in most cases but the real problems on Venus are related to the sulfuric acid and the paucity of certain elements, not problems connected with anthropogenic global warming.
A credible scientist would know enough to recognise that we do not understand the limits of life based on known terrestrial biology, let alone that based on unknown terrestrial or even non-terrestrial biology.
> What makes you think that?
It's what life does. There are other species now that we are learning are moving in that direction. We're going to make machines that do it. Everything from the composition of the universe up seems intended to lead to life and beyond.
> After all it's only happened once so far in 4.6 billion years.
You don't know that, and nor does anyone else.
> And that was only down to the chance collision of a stray asteroid 65 million years ago.
There are been plenty of mass extinctions over the aeons. It wasn't simply dinosaurs *bang* humans you know.
Post edited at 22:54