By Suzanne Goldenberg, The Guardian.co.uk
No mention of global warming for the first time since Congress was briefed on the threat in 1988
The Pentagon ranks it as a national security threat and, left unchecked, climate change is expected to cost the US economy billions of dollars every year - and yet it has proved the great unmentionable of this election campaign.
Amid unprecedented melting of the Arctic summer sea ice, new temperature records in the US and a historic drought, the last of three presidential debates wound up on Monday night without Barack Obama or Mitt Romney ever uttering the words climate change.
It was the first time since 1988, the year Congress was first briefed on the emerging threat by the scientist James Hansen, that there had been no mention of climate change in an election debate.