Al Gore has sought to inject fresh momentum into the Copenhagen build-up, saying he is certain Barack Obama will attend and predicting a rise in civil disobedience against fossil-fuel polluters unless drastic action is taken over global warming.

Amid increasing incidents of climate protesters disrupting the operations of fossil-fuel industries and airports in Britain and elsewhere, Gore suggests the scale of the emergency means non-violent lawbreaking is justified. "Civil disobedience has an honourable history, and when the urgency and moral clarity cross a certain threshold, then I think that civil disobedience is quite understandable, and it has a role to play," he says. "And I expect that it will increase, no question about it."

In his only UK newspaper interview to mark the publication of his new book, entitled Our Choice, Gore says it is crucial for Obama to attend Copenhagen in person, adding: "I feel certain that he will."

He remains optimistic, he insists, that the US Senate will pass a climate change bill before Copenhagen – a move widely seen as vital for persuading the world, especially developing countries, that the US is serious about reducing emissions.

But Gore was speaking before reports this week that Harry Reid, the Senate Democratic leader, would back Republican demands for a full cost analysis of any such legislation – a process that could take five weeks, postponing debate until after the Copenhagen summit.

On Thursday the UK climate change secretary, Ed Miliband, acknowledged that hopes were fading that Copenhagen would result in a full treaty.

Nevertheless, there are "surprises … in store" on a potential Senate bill, Gore says, citing confidential conversations between Democrats and Republicans in which he has been involved. This week Democrats made small but significant progress when they pushed the bill through a vital committee stage despite a Republican boycott.