PM launches next UN climate change conference - COP26 - to be held in Glasgow later this year
He sets out plans to ban the sale of petrol, diesel or hybrid cars by 2035
Sir David Attenborough joins him for the event at London's Science Museum
Boris Johnson also launches a 'Year of Climate Action' in the UK
He says he wants to achieve the target of emitting virtually zero carbon by 2050
It comes as sacked head of COP26 attacks the PM over his handling of the summit
We're winding up now - if you want the detail of today's announcement, read our story on it here.
And if you want more on the issue of climate change, here are a few suggestions:
The PM's official spokesman says Downing Street has “no comment” to make on a letter written by COP26's former president Claire O’Neill, in which she accuses him of failing to support her work.
He thanks Ms O'Neill for her work towards COP26, and says details about her replacement - which will be a "ministerial post" - will be set out "in due course".
Asked about Ms O'Neill's comments that the PM doesn’t understand climate change, the spokesman points to the PM's speech and says the government is “going to ensure COP26 is a successful event”.
He dismisses the idea that the conference might be moved from Scotland to England.
Image source, Getty ImagesAs we told you earlier, while Boris Johnson has been launching COP26, he has been accused of a "failure of vision and leadership" by the woman who was in charge of preparing for that conference.
Claire O'Neill was sacked last week, and says the prime minister admitted to her that he "doesn't really get" climate change.
You can watch Mrs O'Neill speaking about this in more detail here.
Image source, PA WireA quick recap of this mornings announcements:
Image source, Getty ImagesSo we've heard that the next UN climate conference will be held in Glasgow. But what is Scotland doing about climate change?
Read up on targets here.
Image source, UK POOLEarlier, Boris Johnson told an audience at the Science Museum that the Earth has gone through a "catastrophic period" when "addiction" to fossil fuels got "out of control".
He added that global warming is now "taking its toll on the most vulnerable populations around the planet".
He also said it was important to link the issues of biodiversity and climate change.
He told the audience that the climate issue can only be solved when the "balance between humanity and nature" is restored.
Here's some more of what Sir David Attenborough said earlier at the launch.
"Now although we have agreed on the problem we have to do something about it," he tells the event.
He says it is "up to us" and co-hosts Italy "to put before the nations of the world what has to be done".
"We don’t need to emphasise," he says, "that the longer we leave it... the worse it is going to get.
"So now is the moment.
"It is up to us to organise the nations of the world to do something about it."
The Scottish government has released a statement on the climate conference and has called for a new president to be appointed "immediately" to replace sacked chief Claire O'Neill.
It says discussions are taking place in relation to costs and Scottish ministers "expect that all costs associated with COP26 will be borne by the UK government".
"This includes funding for police as well as the fire and ambulance services to both prepare for and deliver a safe, secure and successful event," it says.
"COP26 is hugely important for tackling the climate crisis and that must be the focus.
"A new president should be appointed immediately to make real progress in building the relationships that will be needed within the UK, and around the world, to deliver a successful outcome from the conference."
BBC Science Editor tweets...
The prime minister is questioned by David Shukman about the sacking of former climate change summit boss Claire O'Neill, and who might replace her. Boris Johnson does not answer the BBC's science editor's questions.
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The leader of Glasgow City Council, Susan Aitken, is at the conference launch.
She says Sir David Attenborough has confirmed the event will be in Glasgow.
It follows a suggestion this morning from sacked conference chief Claire O'Neill that there was doubt whether it would be held there or at an English location.
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Prime Minister Boris Johnson and Sir David Attenborough met some primary school children before speaking to experts, campaigners and politicians at the Science Museum in London.
Mr Johnson told them: "We want to get everybody to agree to use new technology such as electric batteries, wind turbines, solar panels, all that kind of thing, so they stop producing so much greenhouse gases."
He said the UK wanted to get to net zero and said "we think we've got to do it" because of Britain's role as a leader in the industrial revolution.
Today Programme
BBC Radio 4
Ed Miliband, a former Labour energy and climate change secretary, says the government needs to do more to make the COP26 summit a success.
"If we're saying to other countries that they've got to raise their ambitions to close the gap, we've got to raise our ambition," he says.
"We've changed our 2050 objective to zero emissions, which is a good thing, but if I was in charge of this issue I'd be saying to the independent climate change committee: 'Give us the advice quickly for how we should raise our ambitions for 2030', because fundamental to Glasgow is saying to other countries: 'You've got to step up, you've got to do more'.
"We'll be in a much stronger position to do that if we ourselves are stepping up our ambition."
David Shukman
Science editor, BBC News
The prime minister says that a "catastrophic addiction to fossil fuels is cloaking the planet like a tea-cosy".
It's taking its toll on the poorest people on the planet, he says, adding that only by repairing damage to the natural world can we address climate change.
He says the UK is calling on every country for credible targets to get to net zero.
"We were the first to industrialise, so we have a responsibility to lead the way," he says.
"People saying it's too expensive are wrong."
David Shukman
Science editor, BBC News
Image source, Getty ImagesSir David Attenborough is talking first, saying that "we all know the dangers" of climate change.
He says: "It's up to us to put us to put before the nations of the world what needs to be done...now is the moment."
He calls it "encouraging" that the UK government has declared a "Year of Climate Action" and he says he is looking forward to COP26 in Glasgow.
Prime Minister Boris Johnson calls it a "defining year of climate action for country and planet".
Scotland's First Minister Nicola Sturgeon tweets to say that her government is supporting COP26.
She says that political differences will not stop them working with the UK government to make it a success.
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Image source, PA MediaThe UK aviation industry is promising to reduce its net carbon emissions to zero by 2050.
The government has pledged to reduce the UK's carbon emissions to "net zero" by 2050.
This means emissions from areas like transport, farming and industry will have to be avoided completely or offset by sucking CO2 out of the atmosphere, for example by planting trees.
Boris Johnson has inherited the pledge from former prime minister Theresa May, who put the commitment into law in June last year.
The target was the subject of debate at December's election, with several opposition parties calling for the date to be brought forward.
The Lib Dems said the date should be brought forward to 2045, whilst Labour said the UK should be put "on track" to achieve net zero "within the 2030s".
The Green Party went even further, calling for net zero to be achieved by 2030.
Our science editor is at the Science Museum waiting for the climate conference launch to begin.
He says that most people seem to be talking about sacked conference head Claire O'Neill.
We've already heard from her this morning - she says the prime minister has said he "doesn't get climate change".
But cabinet minister Michael Gove says he disagrees with her, adding that Boris Johnson describes himself as a "green Tory".
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Greenpeace's policy director Doug Parr says he wants to see the government "rise above petty politicking and actually deliver the right sort of environment, the right sort of conference".
"What we need now is for this conference to be a success, it should be right at the heart of the Johnson government," he says.
"Everybody’s got to be engaged in this to make it happen."
He calls the proposed ban on new petrol and diesel cars in 2035 a "step forward" but "it really ought to be brought forward to 2030 as so many other countries have done in Europe".
"We need to move quicker to match what’s going on elsewhere in the world," he says.
Image source, Getty ImagesFlying is not "the enemy" in the fight against climate change, the chief executive of Heathrow Airport has said.
John Holland-Kaye told the BBC's Today programme: "The answer is not to stop people flying. It has to be about decarbonising aviation."
The UK's aviation industry is promising to reduce its net carbon emissions to zero by 2050.
Cleaner engines, new fuels and planting trees will all help, according to the industry group Sustainable Aviation.
Friends of the Earth's Mike Childs says the government is "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 says.
He says the government could show “real leadership" ahead of COP26 by reversing plans to develop "climate-wrecking roads and runways".