The US has unveiled an updated carbon pledge that will see its emissions nearly halved by 2030
President Joe Biden will host 40 leaders at a virtual summit in the White House to raise ambition on tackling climate change
The meeting will aim to re-assert US global leadership in the area after President Trump pulled the country out of the Paris agreement
President Biden has made the climate a key focus for his administration, re-joining the Paris agreement on his first day in office
Ahead of the meeting, officials urged greater ambition, particularly among countries perceived as "laggards" on climate
The leaders of China, the UK, India, Canada, France, Germany, South Africa, Bangladesh, Indonesia and Russia are all attending
Observers have been closely watching China - the world's top emitter - for any commitments it might make at the meeting
Image source, PoolEmmanuel Macron, the French leader, starts speaking.
Alas, there is no translator around.
His feed is abruptly cut off and confusion reigns temporarily as moderators try to move on to Russian president Vladimir Putin.
Putin sits silently for a moment, unaware that it is his turn to speak.
Image source, PoolChancellor Angela Merkel calls the climate fight "a Herculean task".
She says both Germany and the European Union are on track to reach net-zero emissions by 2050.
She calls carbon pricing, already implemented in Germany, "the right way forward" and says the country is both investing in renewable energy and phasing out coal.
Germany has doubled its financing of the global climate fight, Merkel adds, and will continue to provide support wherever possible.
Image source, PoolThe next leader to speak is Prime Minister Sheikh Hasina of Bangladesh.
She thanks the US for rejoining the Paris climate accords and re-engaging with the world in the climate fight.
Bangladesh is "a climate-vulnerable country" and therefore represents the interests of other small developing nations with similar vulnerability, says Hasina.
She points out they spend millions on climate-resilience and mitigation measures, and calls on the developed world to help lead that fight.
Image source, pool"You can no longer pollute in Canada for free," says Prime Minister Justin Trudeau of Canada.
He encourages other countries to follow Canada's lead as well as pledging to cut Canada's emissions even further.
"Today, Canada is in a position to raise our climate ambition once again. Our new climate target for 2030 is to reduce our 2005 emission levels by 40-45%."
Matt McGrath
Environment correspondent
China's President Xi Jinping re-iterated his previous commitments to peak China's carbon dioxide emissions before 2030 and achieve carbon neutrality before 2060.
While giving no new undertakings, Mr Xi hinted that coal may have a limited role in China's future.
According to Mr Xi, China "will strictly control the coal-fired power generation projects".
"We will strictly limit the increase in coal consumption over the 14th five-year plan period and phase it down in the 15th five-year plan period."
The 15th five-year plan will run from 2026.
Right now, coal is still king.
According to the International Energy Agency, China will be responsible for around half the growth in coal around the world this year, as economies recover from covid.
Image source, Getty ImagesPrime Minister Yoshihide Suga of Japan is now up.
Suga was the first world leader to meet President Biden face-to-face, at the White House earlier this week. Like the other leaders, he begins by commending Biden for calling today's summit.
"Japan is ready to demonstrate its leadership" on this issue, Suga says, and will reach its decarbonisation targets.
Suga pledges that Japan will aim to reduce emissions by 46% in 2030 compared to 2013 levels. Previously the country had pledged only a 26% cut in emissions.
Making Japan a greener society has been a top priority for Suga and he adds it will continue to push an ambitious top-level target for cutting carbon emissions.
The summit has started off with strong statements from leaders, but the tech team is clearly still getting the hang of operating a virtual worldwide conference.
Vice-President Kamala Harris' opening speech featured an echo of her saying the same speech, clearly the translation feed, that was unintentionally left on.
China's President Xi Jinping had no translation for the beginning of his speech.
And as Prime Minister Yoshihide Suga of Japan spoke, you could hear a tech operator say over him, "OK, Germany is up next".
Image source, PoolBoris Johnson is up next.
He thanks President Biden for returning the United States to the front of the fight for climate change and calls his announcement about cutting US greenhouse gas emissions "game-changing".
The UK is doing the same, he says.
"We can do this together across the world. It's going to mean the richest nations coming together and exceeding the $100b commitment they already made in 2009."
Johnson ends his speech by saying "we can build back better, by building back greener", referring to the job creation that can come with combatting climate change.
Reality Check
Most of us have heard of a carbon footprint by now - the amount of greenhouse gases released into the Earth’s atmosphere due to the activities of an individual or an organisation.
But what are these activities? And how do you reduce your carbon footprint?
There’s the direct impact of the energy we use to travel or power our homes.
Flying less and cutting down on the use of petrol or diesel cars can help lower your footprint.
There’s also the indirect impact as a result of the energy used to produce all the things we consume.
BBC Reality Check takes a look at ways we can change how we live to make a difference:
Image source, PoolPrime Minister of India, Narendra Modi, is the next world leader to speak.
"Humanity is battling a global pandemic right now and this event is a timely reminder that the grave threat of climate change has not disappeared," he says.
Climate change is "a lived reality" for millions and requires "concrete action", says Modi.
The Indian leader says the country has taken "bold action" with large-scale renewable energy development, afforestation and other moves.
He hails India as having a level of carbon emissions per capita to be 60% below the global average, and says it is because his countrymen's lifestyles are still "rooted in traditional practices".
"This shows the importance of lifestyle change" in the climate fight, Modi points out.
Image source, PoolThe summit is experiencing a few technical glitches with the translation feed, but appears to be smoothing it out.
China's President Xi Jinping is up next via video conference.
"We must be committed to harmony between man and nature," says President Xi.
He reiterates China's climate promises, including moving to sustainable energy sources and achieving carbon neutrality by 2060.
"China looks forward to working with the international community, including the United States," says President Xi.
Prime Minister Narendra Modi of India is up next.
United Nations Secretary General Antonio Guterres is now up, speaking on how to build a "net-zero climate coalition".
He lauds President Biden for his push to halve emissions by 2030, saying: "You have started the summit by talking the talk".
Guterres calls for phasing out coal, better financing and support for developed countries, and an end to the "war on nature".
Urging decisive action, he tells world leaders: "We are at the verge of the abyss, we must ensure that the next step is in the right direction."
Image source, Pool"This is a decisive decade," says President Biden.
"The steps our countries take between now and Glasgow will set our world up for success."
The UN Climate Summit will take place in Glasgow later this year.
"This is a moment of extraordinary possibility," he says, before ending his opening remarks.
The summit now turns to a round table of leaders and US Secretary of State Tony Blinken begins speaking.
"The cost of inaction keeps mounting. The United States isn't waiting. We are resolving to take action."
President Biden drills home the message that he sees combating climate change as an important way to create jobs, a political promise of his administration.
"By putting these people to work the United States aims to cut greenhouse gases in half by the end of this decade."
"We have to step up," he says.
"Together we come from very different places but we share this common concern," says Vice-President Kamala Harris.
She spoke about the wildfires in California that have grown in intensity before introducing President Biden.
"Meeting this moment is about more that preserving our planet," he says. "It's also about providing a better future for all of us."
The Leaders Summit on Climate has opened with an inspirational video about the need to combat climate change featuring pre-recorded videos from leaders around the world.
US President Biden and Vice-President Harris are expected to speak soon.
Matt McGrath
Environment correspondent
Image source, Getty ImagesThe Pope meeting with Vice President Biden back in 2016
Among the political leaders attending today's virtual Biden summit, there will also be a spiritual one in Pope Francis.
Climate change has been a major theme in his papacy, the importance of which he set out in his 2015 encyclical Laudato Si.
Given his involvement in this climate gathering, might it be a hint that the Pope will travel to Glasgow in November to attend COP26?
Matt McGrath
Environment correspondent
Image source, Getty ImagesJapan's prime minister gets his announcement of a new target in early
It looks like an early win for the Biden summit.
Wire reports suggest that Japan has responded to pressure from the US and from environmental groups by upping its emissions cutting pledge for 2030. Their new target will be a 46% cut in carbon by the end of the decade compared to 2013 levels.
"We aim to cut greenhouse gas (emissions) by 46% in fiscal 2030 from fiscal 2013," prime minister Yoshide Suga told a meeting hours before the discussions called by US President Joe Biden begin.
Japan's previous goal, often derided as inadequate by campaigners, was a 26% cut by 2030.
Matt McGrath
Environment correspondent
The US has pledged to cut carbon emissions by 50-52% below 2005 levels by the end of this decade.
This new pledge, which will be unveiled at virtual summit of 40 global leaders, essentially doubles their previous promise.
The Americans hope that their ambitious new plan will encourage China, India and others to go further before the crucial COP26 meeting, in Glasgow in November.
But there will be some scepticism about the ability of the US to deliver on their new target, given the divided nature of American politics.
Many commentators had pushed the US to go for a 50% cut in emissions as a clear signal of intent.
The fact that President Biden is prepared to go slightly beyond this level will be a welcome surprise to many scientists and campaigners.
“By announcing a bold target of cutting emissions 50-52% below 2005 by the end of the decade, President Biden has met the moment and the urgency that the climate crisis demands, said Nathaniel Keohane from the US Environmental Defense Fund.
“This target aligns with what the science says is necessary to put the world on the path to a safer climate, and vaults the U.S. into the top tier of world leaders on climate ambition.”
Biden: 'Time to act' on climate crisis
While campaigning for the presidency, Biden was criticised by the left wing of the Democratic Party for not signing up to the highly ambitious Green New Deal.
He answered his critics by promising he would make the environment a key plank of his presidency.
Here are a few things he’s achieved so far:
A new US carbon-cutting pledge for 2030 is expected, possibly today at the start of the summit. But Biden will face questions about what steps the world’s largest polluter, historically, will take to meet it.
Read more: What US rejoining Paris means https://www.bbc.co.uk/news/science-environment-55732386