London
He told leaders Monday that "we are in roughly the same position" only now the "ticking doomsday device" is real and not fiction.
He was kicking off the world leaders' summit portion of a UN climate conference, which is aimed at getting agreement to curb carbon emissions fast enough to keep global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) below pre-industrial levels.
Britain's leader struck a gloomy note on the eve of the conference, after Group of 20 leaders made only modest climate commitments at their summit in Rome.
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