"On any kind of pragmatic timescale, I think we should see loss of the Amazon forest as irreversible."

Chris Jones, Met Office Hadley Centre, Exeter, UK

"I'm frustrated, as are many of my colleagues, that 30 years after the US National Academy of Sciences issued a strong warning on CO 2 warming, the full urgency of this problem hasn't dawned on politicians and the general public."

Stefan Rahmstorf, Potsdam Institute for Climate Impact Research, Germany

"Ice loss in Greenland has accelerated over the last decade. The upper range of sea level rise by 2100 might be 1 metre or more."

Konrad Steffen, University of Colorado, Boulder

"Do the politicians understand just how difficult it could be, just how devastating 4, 5, 6 degrees centigrade would be? I think, not yet."

Nicholas Stern former UK government economics adviser