“There can be no greater responsibility than protecting our planet, and no mission that a Global Britain is prouder to serve,” he will tell a London reception attended by David Attenborough.
However, the flagship announcement – to end sales of new polluting cars in 2035, rather than 2040 – will still fall short of the call by his independent climate advisers to act by 2030.
The government has faced growing criticism that it has failed to announce practical measures to achieve the net zero target, despite hailing it as a world-leading measure.
Mr Johnson barely mentioned the climate crisis during the election campaign – and a strategy for achieving net zero emissions will not emerge until the end of the year.
The speech on Tuesday is intended to launch the strategy for delivering success at the crucial ‘COP26’ summit in Glasgow in November, which the UK will host on behalf of the United Nations.
It is widely seen as the last realistic chance for countries to pledge the deep cuts in emissions to hold global heating to no more than 2C – and prevent catastrophic climate change.
She will be replaced by a minister, in a reshuffle expected next week, but that in turn has prompted fears of a conflict with the desire to strike post-Brexit trade deals, downgrading carbon commitments.
In the Commons, Rachel Reeves, the newly-elected chair of the business, energy and industrial strategy committee, tore into the “chaos and confusion”.
“Hosting the global climate conference COP26 is a huge opportunity for Britain to tackle the climate emergency and play an international leadership role,” she said.
“The prime minister has failed to chair a single meeting of the climate Cabinet committee and now he has sacked the conference president. Why is that?”
At the reception, the transport secretary Grant Shapps will announce a consultation on ending sales of petrol and diesel cars, including hybrids, by 2035 or “earlier if a faster transition is feasible”.
He will claim the switch to electric cars “is working”, adding: “We want to go further than ever before. That’s why we are bringing forward our already ambitious target to end the sale of new petrol and diesel cars.”
Giuseppe Conte, the Italian prime minister, will attend the event, along with prominent British figures from climate science and business.
“2020 must be the year we turn the tide on global warming – it will be the year when we choose a cleaner, greener future for all,” Mr Johnson will say.
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