Rei
This is an example of the serious problem the political processes have when dealing with developing areas in science. The current state of knowledge can not tie up all the loose ends yet.
We have a general consensus among atmospheric researchers on global warming but we do NOT have unequivical proof. And the political decision makers want to be absolutely sure.
This wouldn't be a problem if we had time to wait and see. Do we? In truth we don't KNOW yet.
What if we act on the advice of he experts and it turns out global warming isn't happening. Let's make a wild assed guess that we spend 50 trillion US$ over the next 25 years that we didn't have to spend. It would have some benefits in technology advances and energy saveings (perhaps). Let's be optimistic and suggest 10 trillion in returns. We just blew 40 trillions. Real money!
What if we accept the idea that global warming isn't happening or that it is ok, in spite of the consensus among those best able to judge. Let's say we are wrong in this?
What are the estimated range of costs here. They vary a lot! It is hard to pin down. At one end we loose some farmland in one place, a few south sea island nations and bangladesh disappear but maybe the costs are only say 10 trillion over the next 50 years. But at the other end ----- we loose Holland, Bangladesh, Florida, Manhatten island the middle of california, LA, half of Seattle, London, Denmark, all of the corn and wheat growing areas of the USA, a larege fraction of the worlds temperate rain forests, etc etc etc. What are the costs then? Lets try 5,000 trillion (dammed if I know).
So what we face is an insurance cost of 40 trillion to cover a risk of between 10 trillion and 5,000 trillion. I'd sure want to narrow those numbers a bit.
And if there are hints that if we start too late we won't be able to stop the warming then I might spend some of that insurance money before I know everything and stop if I turn up evidence that I am wrong.
(btw - i don't think we know what the upper limit to the risks of ignoring global warming are)