Thousands of people, including primary school children and members of the Women’s Institute, have lobbied MPs, calling for urgent action to tackle the climate emergency and critical loss of nature.

About 12,000 people gathered in Westminster on Wednesday to put pressure on politicians, according to the organisers the Climate Coalition and Greener UK, whose members include aid agencies, social groups and conservation organisations.

The Time Is Now lobby comes after months of growing environmental protests, from school strikes to actions by members of Extinction Rebellion, and increasing warnings of the need for unprecedented action to tackle the global climate.

Gareth Redmond-King, head of climate change at WWF, said: “Public concern is at its highest level. It is a mainstream issue. There are lots of organisations working hard to raise the profile and focus their MPs’ minds on policies and actions to make sure we take action.”

A recent survey showed two-thirds of Britons wanting faster action to tackle climate change.

Q&A Why is the Guardian changing the language it uses about the environment? Show The Guardian has updated its style guide to introduce terms that more accurately describe the environmental crises facing the world. Instead of “climate change”, the preferred terms are “climate emergency, crisis or breakdown” and “global heating” is favoured over “global warming”. The scale of the climate and wildlife crises has been laid bare by two landmark reports from the world’s scientists. In October 2018, they said carbon emissions must halve by 2030 to avoid even greater risks of drought, floods, extreme heat and poverty for hundreds of millions of people. In May 2019, global scientists said human society was in jeopardy from the accelerating annihilation of wildlife and destruction of the ecosystems that support all life on Earth. The editor-in-chief, Katharine Viner, says: “We want to ensure that we are being scientifically precise, while also communicating clearly with readers on this very important issue. The phrase ‘climate change’, for example, sounds rather passive and gentle when what scientists are talking about is a catastrophe for humanity.” Other terms that have been updated include the use of “wildlife” rather than “biodiversity”, “fish populations” instead of “fish stocks” and “climate science denier” rather than “climate sceptic”. Damian Carrington Environment editor

Theresa May, in one of her last acts as prime minister, is signing into law a target of net zero greenhouse gas emissions by 2050, which was being debated by the Lords on Wednesday.

Campaigners, religious leaders and people of various faiths, led by the former archbishop of Canterbury Rowan Williams proceeded along Whitehall on a “walk of witness”.

Williams said he was proud the UK was taking the climate crisis seriously. “I compare it with the great struggle 200 years ago with ending the slave trade. Parliament took an option that wasn’t easy, it must have felt risky at the time facing massive entrenched global culture – and things changed,” he said.

At least 195 MPs who met campaigners were encouraged to mark their constituency with a pin on a large map of the UK before being taken by rickshaw to speak to their constituents.

At 2pm the thousands present rang alarm clocks, mobile phone alarms and sirens, and cheered loudly to symbolise “the time is now”.

Jane Alexander, a primary school headteacher from London, brought five pupils from her school, North Harringay primary, to the lobby. She said: “Our children may be too young to vote but they are not too young to have their voices heard.”

Michelle Lowe, from Winchester, said she had joined the mass lobby to speak to her MP because “the time is now”. She said: “I have children, who are 22, 20 and 16, and I’m worried about their futures.”

The Liberal Democrat leadership contender Sir Ed Davey was among MPs who met constituents. He said it was absolutely clear that the British public was telling politicians to get tough on climate change.

Benjamin Halfpenny, from Greener UK, said one of the demands made of MPs was for a strong environment bill to tackle air pollution, water quality and declines in wildlife such as hedgehogs.