Since its launch last year, members have shut bridges, poured buckets of fake blood outside Downing Street, blockaded the BBC and stripped semi-naked in Parliament.
It has three core demands: for the government to "tell the truth about climate change", reduce carbon emissions to zero by 2025, and create a citizens' assembly to oversee progress.
Controversially, the group is trying to get as many people arrested as possible.
One of the group's founders, Roger Hallam, believes that mass participation and civil disobedience maximise the chances of social change.
Oxford Circus is usually one of the busiest crossroads in London, but only scores of protesters and bemused onlookers can be found in the middle of the road today.
Food stalls offering free porridge, and clothing lines for dirty laundry have been erected.
Children as young as six are making use of the freshly-drawn hopscotch, running around the tents and flying colourful banners.
One campaigner, who attended the protest with her two children, says she was protesting for the people who are "the most vulnerable, and least responsible for climate change".