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A global conference attracting global protest. Demonstrators were on the streets in

cities worldwide. Like me, the protesters have seen it all before, another climate

conference, more dashed hopes for scientists worried about the planet. But while the

noise outside is an echo from previous years, the noises coming from inside the conference

are very different. There's much more of an atmosphere of hope, of cooperation, a feeling

that perhaps we're reaching a tipping point in political will on climate change.

It's essentially the breakthrough that we have been looking for for 10 years in the climate

negotiations. I'm very impressed, very, very impressed. It has gone beyond our best case scenario

of wireless imagination. To appreciate how far the world has moved, we need to cast back to the

Shambolic UN conference in Copenhagen in 2009. After nearly two weeks of torturous and often

bitter debate, the climate change summit in Copenhagen has ended, without legally binding agreement

that many had wanted. China took much of the flak for the failings of that conference,

but in truth many were to blame, including the US, as the summit collapsed with no deal on

curbing emissions. The trust wasn't there between rich nations and poor, the will was missing.

To turn around in expectations this time, has surprised climate analysts like Bill Hare.

It would have been very difficult to predict in the dark period after Copenhagen,

absolutely. So it is a positive, and I think the trick now is to capture that momentum.

I'm Roger Haribin, and in this week's edition of changing climate change on the BBC World Service,

we're going to investigate exactly what has changed.

Well, this is one huge change. So on the computer in front of me, I've got a list of more than

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