The first person to face trial over the Extinction Rebellion protests in April has been found guilty of a minor public order offence for blocking a road in central London.

Angie Zelter, 68, was given a conditional discharge at Hendon magistrates court on Tuesday after being arrested for lying in the road near Parliament Square on 17 April. She had been taking part in protests in which thousands of people blocked key sites across the capital over 10 days to highlight the escalating climate emergency.

Defending herself, Zelter outlined the “clear and unequivocal” scientific evidence of climate chaos and the threat ecological breakdown posed to the future of humanity, citing a swath of scientific studies, UN-backed reports and academic papers.

She told the court that although this was only a “dry summary” and a “minute fraction” of the available evidence, it proved that her peaceful civil disobedience was both necessary and proportionate.

Zelter told magistrates that humans faced mass extinction unless governments implemented wide-ranging changes.

Q&A What is Extinction Rebellion? Show Extinction Rebellion is a protest group that uses non-violent civil disobedience to campaign on environmental issues. Launched in October 2018, with an assembly at Parliament Square to announce a 'declaration of rebellion' against the UK Government, the group has staged regular demonstrations against current environmental policies. More than 1,000 activists were arrested in April 2019 after protesters occupied four sites across London, as well as blocking roads, disrupting a railway line and conducting a protest at Heathrow. Other demonstrations have included a semi-naked protest inside the House of Commons and blockading streets in London, Cardiff, Leeds, Bristol and Glasgow. The group says climate breakdown threatens all life on Earth, and so it is rebelling against politicians who “have failed us”, to provoke radical change that will stave off a climate emergency. The movement has become global with groups set up in countries include the US, Spain, Australia, South Africa and India. Martin Belam Photograph: Anadolu Agency/Anadolu

The judge, Margot Coleman, said that although she was mindful of the evidence from Zelter, the case “was a matter of law not morality”. “Your argument does not provide you with a defence to these charges,” she said.

Zelter, who has been involved in various campaigns concerning the arms trade, environmentalism and nuclear weapons since the early 1980s, was convicted of breaching a section 14 order, which the court heard had been imposed because the Extinction Rebellion protests were causing widespread disruption to businesses and the wider community. The order gives police the power to clear static protests from a specified area.

The court heard she had been lying in the road near Parliament Square and refused to move when asked to do so by the police.

Zelter disputed the implementation of the section 14 order, arguing the disruption was minimal compared with the “chaos that will ensue from climate breakdown”.

“I am fearful for the future for myself, for my family and for all living creatures on this fragile planet,” she said. “I believe there is a real and substantial threat to all our lives, and that, in accordance with the science, urgent and systemic changes to our society must be taken now to mitigate the danger. That is why I took action.”

Zelter said her history of campaigning and protests – she has established various protest groups and been arrested and imprisoned several times – proved she had not made the decision to take part in the Extinction Rebellion action lightly.

“I hope it shows that my actions … were not taken spontaneously or lightly but came out of [a] lifetime [of] concerns and that I have tried everything I could think of to create the changes necessary to combat climate change and prevent catastrophic collapse.”

She said the overwhelming evidence of climate breakdown had left her feeling “frustrated, depressed and, at times, hopeless”.

“I cannot really understand why those ‘in power’ have refused to act. After all, it is their world too … ” she said. “When our society and ecosystem collapses around us, none of us will be able to eat, drink, or breathe money.”

Coleman ordered her to pay £640 costs, but Zelter said she would not.

Speaking outside the court she said she was considering an appeal. “I am sad that the judge did not take the broader view of finding me not guilty because of the severity and urgency of the climate emergency,” she said.