A fifth of London’s schools are now susceptible to flooding and millions of people living in the capital are at “high risk” of suffering from the effects of the climate crisis, according to analysis from City Hall, as Sadiq Khan warns time is running out to tackle the issue.

In a speech on Thursday, the London mayor is due to pile pressure on the UK government to ensure bold action is taken when it hosts world leaders for Cop26 in Glasgow in two months’ time, and add that without a significant commitment there will be “catastrophic” impacts on the environment and air quality.

The outcome of the UN conference will “determine whether we are going to avert the worst consequences of climate change, which could be devastating”, Khan is expected to say, alongside the launch of a public awareness campaign designed to encourage residents, communities and businesses in London to do their bit.

Figures have been published by the London mayor’s office showing that 200,000 homes and workplaces, as well as 25% of rail stations in the capital and 10% of the network, are at high risk of flooding if extreme temperatures and flooding get worse. The six boroughs at the highest risk are Hackney, Hammersmith and Fulham, Islington, Brent, Tower Hamlets and Newham.

London needs to become “greener, fairer and more prosperous for everyone”, the mayor will say, defending the expansion of the ultra-low emission zone up to the North and South Circular – taking in about 3.8 million people – that will come into force from 25 October. City Hall calculated the move would reduce road nitrogen oxides emissions by about 30%.

Khan is due to say: “The climate emergency remains one of the biggest threats London and the world faces. Average temperatures around the world, including in London, are already increasing. This summer, we saw the impact of the climate emergency first-hand with soaring temperatures and flash floods in London.”

He will recommit to London becoming a zero-carbon city by 2030 and announce that planning policies have led to on-site carbon reduction resulting in 44,000 tonnes of carbon saved a year – almost 50% more than set by building regulations.

Khan is expected to add: “We are delivering a climate action plan that is compatible with the highest ambition of the Paris agreement. I also want London to be a zero-pollution city so that no child has to grow up in our city breathing toxic air. That’s why I’m expanding the ultra-low emission zone next month.

“But I can’t do it all alone. That’s why today I’m launching my city-wide campaign to inspire all Londoners – individuals, businesses and communities – to take action. I also want to work with the government to unlock the powers and funding needed to meet our targets, which will help deliver national targets too.”