Why did Copenhagen fail to deliver a climate deal?

About 45,000 travelled to the UN climate summit in Copenhagen – the vast majority convinced of the need for a new global agreement on climate change.

So why did the summit end without one, just an acknowledgement of a deal struck by five nations, led by the US.

And why did delegates leave the Danish capital without agreement that something significantly stronger should emerge next year?

Our environment correspondent Richard Black looks at eight reasons that might have played a part.