Copenhagen Sketch: At last, a ray of light amid the gloom – Arnie's in town

He's an action hero in movies and a climate action hero for the globe

For the first time since negotiations began more than a week ago, a huge cheer erupted in the cavernous main chamber of the Bella Centre yesterday afternoon. People on the fringes rushed to see the source of the commotion – had there been a sudden breakthrough in the deadlocked talks? No. The spontaneous applause heralded the arrival of Arnold Schwarzenegger.

The Governor of California arrived in Copenhagen with a spring in his step and sunshine in his heart, determined to provide its increasingly morose participants at the summit with a dose of Austrian-American optimism. Hundreds of campaigners and journalists packed into the room where Arnie was due to speak. "He's an action hero in the movies and a climate action hero for the globe," gushed Gordon Campbell, the premier of British Columbia.

"Thank you for such a wonderful introduction – it's exactly how I wrote it," quipped Schwarzenegger. "I love giving these kind of speeches, simply because I'm not the only one who has an accent."

He had, he said, been to Copenhagen many times before – but admitted that these past visits were prompted by "movie promotions and bodybuilding and weightlifting seminars", rather than a determination to secure the future of the planet. Now, though, his aim was different: he praised the work of entrepreneurs, scientists and activists, and downplayed the idea that the lack of an agreement at the end of the week meant failure. "Movements begin with people, not governments," he said, urging the UN to organise another summit to discuss localised ways of fighting climate change.

The cheerful tone set by "The Governator" did not last long – especially for those who heard Al Gore speak shortly afterwards. The former US vice-president depressed his audience into submission with warnings about rising ocean acidity, the loss of coral reefs and the threat to the Amazon rainforest. "Let's not turn Copenhagen into Doha," he said, at the risk of offending any Qataris who might have been in the audience.

More upbeat was London Mayor Boris Johnson. "We need to stop overdosing on gloom, and start conveying a message of optimism to people [that] they can improve their lives and cut their CO2. There's too much mortification of the flesh and hairshirt-ism, too much gloom, too much negativity," he said.

Among the many Schwarzenegger fans present was John Prescott, the former deputy prime minister, who rolled into the Danish capital yesterday to fill his role as the rapporteur for climate change for the Parliamentary Assembly of the Council of Europe. A veteran of Kyoto, he is campaigning for a fairer deal for developing countries, and shared a plane with the Hollywood star on the way over.

"We had a chat about the American petition and how it comes across," he said. "That's the great thing about a place like this hall – you can meet people all the time, everything's going on, you're walking and talking all the time."

Prezza, like many others attempting to enter the Bella Centre, fell foul of the UN accreditation system and was left out in the cold for three hours. "I was absolutely frozen," he raged. "It's all right the blooming NGOs flooding in, but if you've got seats in the hall and you're there to move around and say something, you've got to wait in the same queue." His son David added: "You know who seemed to get in OK? Nick Griffin."

Yes, the leader of the British National Party (BNP), who has described climate change as a "hoax", was here, one of 15 representatives chosen to speak on behalf of the EU. "I feel obliged to point out that there's not a consensus on man-made global warming, and there's not a mandate for the politicians to tax people as a result," he told The Independent, adding that over-investment in biofuels would create a famine that would be "far worse than the effect of the regimes of Stalin and Mao put together".

"If people disagree with my point of view then I'm happy to have a debate," he said. "But I don't think anyone's going to attack me while I'm here."

Whatever you say about the leader of the BNP, he isn't afraid of tempting fate.