A ban on selling new petrol, diesel or hybrid cars in the UK will be brought forward from 2040 to 2035 at the latest, under government plans.
The change comes after experts said 2040 would be too late if the UK wants to achieve its target of emitting virtually zero carbon by 2050.
Boris Johnson unveiled the policy as part of a launch event for a United Nations climate summit in November.
He said 2020 would be a “defining year of climate action” for the planet.
The summit, known as COP26, is being hosted in Glasgow. It is an annual UN-led gathering set up to assess progress on tackling climate change.
Sir David Attenborough said at the launch event at London’s Science Museum that he was looking forward to COP26 and found it “encouraging” that the UK government was launching a “year of climate action”.
“It’s up to us to put before the nations of the world what needs to be done. Now is the moment,” he added.
Mr Johnson said the ban on selling new petrol and diesel cars would come even earlier than 2035, if possible.
Hybrid vehicles are also now being included in the proposals, which were originally announced in July 2017.
People will only be able to buy electric or hydrogen cars and vans, once the ban comes into effect.
The change in plans, which will be subject to a consultation, comes after experts warned the previous target date of 2040 would still leave old conventional cars on the roads following the clean-up date of 2050.
Mr Johnson said the 2050 pledge was necessary because the UK’s “historic emissions” meant “we have a responsibility to our planet to lead in this way”.
The announcement comes as COP26’s former president Claire O’Neill, who was sacked on Friday, wrote a bitter letter accusing Mr Johnson of failing to support her work.
Mr Johnson did not answer the BBC’s David Shukman’s questions about the row.
Mr Johnson said: “Hosting COP26 is an important opportunity for the UK and nations across the globe to step up in the fight against climate change.
“As we set out our plans to hit our ambitious 2050 net zero target across this year, so we shall urge others to join us in pledging net zero emissions.
“There can be no greater responsibility than protecting our planet, and no mission that a global Britain is prouder to serve.”
The prime minister added that a “catastrophic period of global addiction” to hydrocarbons had led to the planet being “swaddled in a tea cosy” of carbon dioxide.
Friends of the Earth’s Mike Childs said the government was “right” to bring forward the ban, but that 2030 would be better than 2035.
“A new 2035 target will still leave the UK in the slow-lane of the electric car revolution and meantime allow more greenhouse gases to spew into the atmosphere,” he said.
He said the government could show “real leadership” ahead of COP26 by reversing plans to develop “climate-wrecking roads and runways”.
AA president Edmund King said: “Drivers support measures to clean up air quality and reduce CO2 emissions but these stretched targets are incredibly challenging.”
The chief executive of the society of motor manufacturers and traders (SMMT) accused the government of “moving the goalposts”.
“With current demand for this still expensive technology still just a fraction of sales, it’s clear that accelerating an already very challenging ambition will take more than industry investment,” Mike Hawes said.
He said the government’s plans must safeguard industry and jobs, as well as ensuring current sales of low emission vehicles were not undermined.
Meanwhile Mrs O’Neill accused Mr Johnson of promising money and people to support her work, but failing to deliver either.
The former Conservative energy minister said: “The cabinet sub-committee on climate that you promised to chair, and which I was to attend, has not met once.
“In the absence of your promised leadership… departments have fought internal Whitehall battles over who is responsible and accountable for [the conference].”
Cabinet minister Michael Gove said Mrs O’Neill was a “close friend” but that he disagreed with her comments.
He told BBC Radio 5 Live Mr Johnson described his own political outlook as “that of a green Tory”.
But Mrs O’Neill added Mr Johnson had “admitted” to her that “he doesn’t really understand” climate change.
“He ‘doesn’t really get it’, I think is what he said,” she told BBC Radio 4’s Today programme in her first interview since being sacked.
Mrs O’Neill said she was “not comfortable with the status quo” and her “absolute desire for action has not been comfortable for some”, adding that this was “not about me” or the prime minister – but about working towards “rapid decarbonisation”.
She said at COP26 the UK must “absolutely double down on taking our great leadership and ambitions in this space, and really energising the world as to why this is a huge opportunity”.
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