On Friday afternoon, two members of Extinction Rebellion, Tamsin Omond and Sara Arnold, spoke at Port Eliot festival in Cornwall to Emily Sheffield, a former deputy editor of Vogue, about the role of the fashion industry in the climate emergency.

Addressing an orangery packed with people who looked as if they knew their way round a vintage boutique, Arnold talked of the need for a “complete cultural change around clothes”.

She also listed a number of facts to convince even the most diehard fashion fan that change is necessary: the industry is set to grow by 63% by 2030; 100bn items are produced each year, “far more than we need”; fashion is a contributor to about 10% of carbon emissions; it is one of the biggest polluters, responsible for the release of a huge amount of microfibres and plastics into the ocean.

Extinction Rebellion, she said, is promoting a fashion boycott, urging people not to buy any new clothes for a year. “We must curb our consumption very, very rapidly … We already produce enough clothes. We can swap clothes between one another, we can customise clothes, we can upcycle them.”

Sara Arnold of Extinction Rebellion at the Fashion Foundation, Port Eliot Festival. Photograph: REX/Shutterstock

The talk took place as part of the festival’s Fashion foundation, where events are taking place all weekend, including from the likes of designer Alice Temperley, and Turner-prize winning artist Jeremy Deller, as well as workshops in brooch-making and “energetic drawing”.

Speaking after the event, Arnold explained more about the boycott’s aims, saying it does not need to mean going without. Indeed, she loves clothes. She trained in fashion design at Central Saint Martins in London and dreamed of being the next Alexander McQueen; she is wearing what Sheffield described as a “frow-ready” outfit – 50s glasses, her mum’s old dress and red lipstick.

It comes down to “challenging your relationship with clothes”, she says. Arnold points out that even with secondhand clothes there are problems, such as whether they are being shipped from afar. “With everything you do, you need to ask questions and challenge … The best thing we can do is swap things with the people that are close to us.”

Sheffield broadened the discussion by asking environmental questions of the audience, including: “How many single-use outfits will the British purchase this summer?” and “How many of those are for festivals?” The answers are 50m and 7.4m respectively. She followed by asking people to raise a hand if they bought a new outfit for the festival. Predictably, no one put their hand up. There was scope for taking heart, though, given the fact that doubling the useful life of clothing from one to two years reduces emissions by 24%.

Extinction Rebellion at London fashion week. Photograph: Yui Mok/PA

Extinction Rebellion is planning disruptions for London fashion week in September. It used direct action last time, blocking roads across the city to hinder those trying to travel from one show to another. For the next instalment, it is planning a funeral for fashion week, because, according to Arnold, “that should be where it stops for ever … During this absolute emergency, celebrating new fashion, which is essentially what fashion week is doing, is not relevant.”

Arnold looked to the example of fashion during the second world war, when, she says, it was frowned upon to wear ostentatious dress. “Yet we are in an existential crisis and fashion weeks are going on as usual,” she said. For Arnold, it is not business as usual. She was working for a luxury brand when the UN Intergovernmental Panel on Climate Change released a special report saying there were 12 years to limit climate catastrophe. The sense of emergency took hold and she “walked out of the job leaving a resignation letter that said ‘we have 10 years left to fight for the planet so, goodbye’”.

Omond agrees that the conversations the industry has need “to be about how we are dealing with the climate emergency and nothing else. That is the state of the emergency we’re in. We need to focus on how we can transition, not in 10 or 20 years, but today or tomorrow. Into a future where we are regenerating the earth rather than ransacking it.”

They looked to the example of the recently cancelled Stockholm fashion week, pledging instead to become a platform that helps the industry be more sustainable. The next London fashion week, she says, “should be a declaration of emergency, not a celebration”. It should “be the death of fashion”, after which there will be rebirth.

Tamsin Ormond, one of the founders of Extinction Rebellion. Photograph: REX/Shutterstock

Omond spoke more broadly about the Extinction Rebellion movement, about its origins and how its rapid growth and success was rooted in the research of two academics, Roger Hallam and Dr Gail Bradbrook, into non-violent civil disobedience. As the black civil rights and Indian independence movements were the defining issues of their era, so climate change, she said, is the defining issue of ours. “What we see is that climate change is not a once-in-a-lifetime or once-in-a-generation or once-in-a-century issue. It is a once-in-a-species moment. It will be our defining moment.”

• This article was amended on 29 July. It is Stockholm fashion week that has been cancelled, not Copenhagen.