Scientific consensus on the problems of global warming has taken a long time to emerge: on its extent; on its causes; and on its predicted consequences. It is just about achieved today. The article sets out the history of the negotiations that have led to the current situation, and then the setback (doubtless temporary, but none the less certain for all that) of the Copenhagen conference. It reminds us of what we know about global warming, and evokes its likely consequences: the deserti­fication of entire regions in the centre of our continents and in the Mediterranean region, reductions in biological diversity, rising sea lev­els, melting polar icecaps, and growing tensions in the energy economy