London’s mayor, Sadiq Khan, has declared a climate emergency and urged the UK government to do more to avert an ecological breakdown that he says poses an existential threat to future generations.

Speaking as City Hall outlined its new climate change plan, Khan said he was implementing measures to protect people from floods, fires and the political upheaval caused by climate change. He accused central government of “dragging its feet” on dealing with these issues.

“We are in the midst of a climate emergency which poses a threat to our health, our planet and our children and grandchildren’s future,” Khan told the Guardian. “City Hall is doing everything in our power to mitigate the risk in London but the stark reality is that we need urgent government action and funding.”

The acknowledgement of the scale and nature of the ecological crisis by the leader of one of the world’s major cities comes amid growing concern about the impact of climate change. A succession of scientific reports have laid bare the scale of the unfolding disaster, including one from the UN that said there were only 12 years left to avert the most extreme consequences of climate breakdown.

On Sunday 100 academics, philosophers and authors wrote to the Guardian to back a new civil disobedience group – Extinction Rebellion – and called for people around the world to rise up and organise against the “paralysis” of political leaders.

Khan’s intervention follows that of civic leaders in the UK and around the world. Last month Bristol declared a climate emergency and set a goal of becoming carbon neutral by 2030, while Manchester said it would become “carbon zero” by 2038. Both are more ambitious than the UK’s national target of an 80% reduction in emissions by 2050. It follows similar moves by several US cities.

Justine Simons, London’s deputy mayor, and Michael Bloomberg, the UN’s special envoy for climate action, with part of Olafur Eliasson’s Ice Watch melting glacier artwork on Tuesday. Photograph: Ray Tang/REX/Shutterstock

London’s existing plan, unveiled by Khan in May, was for the city to be carbon neutral by 2050. But last week the London Assembly passed a motion saying that target should be brought forward to 2030 and called on Khan to draw up “a specific emergency plan”.

Caroline Russell from the Green party, who proposed the motion, said it was crucial Khan backed a more radical target and called on the government to give him the appropriate powers and funding.

“Catastrophic climate breakdown might be as little as 12 years away,” she said. “This would have profound impacts on every aspect of our lives in London from flooding and overheating in summers, disruption in our food supply chains as well as in the wider natural world.

“The mayor needs to be at the forefront of this challenge, declaring a climate emergency and an urgent updating of his carbon reduction targets to make London carbon neutral by 2030, decades ahead of his current plans, setting a precedent for other major and world cities.”

Khan said he had already introduced a series of measures to tackle climate breakdown – from investing £500m in low carbon technologies to divesting pension funds from fossil fuels.

But he said a City Hall analysis due to be published on Wednesday showed London would need a huge programme of investment as well as new powers to bring forward its zero-carbon target to 2030. The cash would be used to:

• Retrofit hundreds of thousands of homes and offices to make them more energy efficient.

• Decarbonise the national grid.

• Install low-carbon heating systems, such as heat pumps.

• Move private and public transport away from diesel and petrol, and towards electric.

Khan said: “My message to ministers is clear – stop dragging your feet and gambling with our future and give London and cities across the UK the real powers and funding needed to protect our future generations.”

The Green party welcomed Khan’s move and backed his call for more help from central government. But Russell said there was more that could be done now. “Sadiq should start this mission by cancelling the Silvertown road tunnel and fighting harder against things that will make the climate crisis worse.

“He should call right now for a halt to climate-wrecking aviation expansion, including at Gatwick, and ask his C40 [global green city network] counterparts to join him.”