President Obama is due to arrive at the UN climate change summit and inject momentum into getting a deal.
It comes amid a freshly leaked document and after his secretary of state, Hillary Clinton, announced a $100bn climate fund.
Rajendra Pachauri, who heads the UN's Intergovernmental Panel on Climate Change (IPCC), tells us how damaging a 1.5C rise would be for some places on the planet.
Congressman Earl Blumenauer from Oregon says Obama and Clinton make a great team and remains optimistic about a deal in Copenhagen.
Former executive director of Friends of the Earth Tony Juniper says we've been here before and the issues are no different than they were 17 years ago.
We also speak to Radiohead frontman Thom Yorke who tells us what he makes of the talks so far.
Also in today's programme, we discuss the state of UK policing.
Former Metropolitan police commander David Gilbertson says anti-terror laws have led some police to see their work as "the front line in the war on terror", an extreme example of the public's rights being shunted aside.
Civil liberties lawyer Anna Mazzola says police attitudes are linked to draconian legislation.
And Guardian reporter Paul Lewis, who broke the story of the death of Ian Tomlinson at April's G20 protests in London, says we citizens must take more responsibility for knowing our rights and appreciating the challenges faced by the modern police officer.
WARNING: contains strong language
