US President Joe Biden's administration has promised to rally the world on climate, as adversaries China and Russia confirmed participation in a summit, and the European Union and Britain locked in far-reaching carbon reductions.
Just three months into office, Mr Biden will tomorrow and Friday welcome 40 leaders for a virtual Earth Day summit, heralding a US return to the climate frontlines amid mounting worries over the rapid heating of the planet.
Officials said that Mr Biden, who is promoting a green-friendly $2 trillion infrastructure package at home, would announce an ambitious new US target for slashing emissions responsible for climate change over the next decade.
"Climate change is a national security issue. It's my belief that no nation can be truly secure without meeting it head on," said Defense Secretary Lloyd Austin, who along with much of Mr Biden's cabinet will participate in the summit.
With Mr Biden's expected announcement at the summit, a senior administration official said the United States was looking for others also "to make announcements to raise their ambition, to indicate next steps that they intend to be taking, to help solve the climate problem."
China confirmed that President Xi Jinping will take part - his first summit, even if virtual, with Mr Biden as president amid soaring tensions between the two powers on issues from human rights to trade to defense.
Xi will give an "important speech" at the meeting, the Chinese foreign ministry said.
His trip comes days after John Kerry, the former secretary of state turned globe-trotting Biden climate envoy, visited Shanghai and reached a joint statement on cooperation.
China is by far the largest carbon producer and with the United States emits around half of the pollution responsible for climate change, meaning any solution is impossible without both countries.
China last year promised to go carbon neutral by 2060 with emissions peaking at around 2030 but it has also kept up reliance on coal, the dirtiest form of energy, and bristled at EU-led calls for a carbon tax that would hit its exports.
Russian President Vladimir Putin - under fire by Mr Biden over Moscow's purported election interference and hacking and the treatment of ailing jailed dissident Alexei Navalny - also accepted the invitation to participate.
"We must respond to the challenges of climate change," Mr Putin said in his annual national address, saying that Russia, the world's fourth largest emitter, needed to adapt its "entire infrastructure."
Waiting for Biden
Environmental watchers and a series of media reports have indicated that Biden may double the US ambitions on climate change.
Former president Barack Obama, after negotiating the 2015 Paris Agreement, promised that the United States would reduce emissions by 26-28 percent by 2025 compared with 2005 levels.
Mr Obama's successor, Donald Trump, pulled out of the Paris accord, calling it unfair to the world's largest economy, but the United States is still largely on track to meet Mr Obama's goal thanks to continued commitment at the level of states, especially California, and a sharp drop in industrial production last year during the Covid-19 pandemic.
But studies say far more needs to be done to meet the Paris goal of checking warming at 2 degrees Celsius (5.4 Fahrenheit) above pre-industrial levels, let alone its aspiration of no more than 1.5 Celsius.
A UN study late last year found that the world is on track to 3 degrees warming - a level at which the planet is forecast to see many glaciers and ice caps melt, low-lying areas submerged and increasingly severe droughts, floods and disasters that could trigger mass migration.
Britain yesterday announced the most ambitious target of any major economy, saying it will slash emissions by 78 percent by 2035 from 1990 levels.
Prime Minister Boris Johnson announced the commitment as Britain prepares to host a UN conference in November in Glasgow which is aimed at raising ambitions beyond Paris.
Following the announcement by former member Britain, the European Union in marathon talks approved a law that confirms the 27-nation bloc's commitment to reduce carbon by at least 55 percent by 2030 compared with 1990 levels.
Some European parliament members had pushed for greater ambition but European leaders, the historic champions of global climate efforts, hailed what they said was at last a legal framework to achieve targets.
"This climate deal is a game changer," the chair of the European Parliament's environmental commission, Pascal Canfin, told reporters.
He said that 52.8% of the cuts would be direct reductions in carbon output with the rest made up by carbon sinks - plants, waterways and other areas that can suck up the pollution.
Environmentalists are urging nations to take immediate action, not just to make longer-term promises.
"To get closer to the 1.5 pathway, significant political will and action are required," said Jennifer Morgan, executive director of Greenpeace International.
"The world's richest countries must do more than just halve their emissions by 2030, having profited from extractive and polluting industries leading to the climate crisis."