US special climate envoy John Kerry said his country was rejoining the effort against climate change as he called for a "warlike enterprise" to tackle global warming.
"We rejoin the international climate effort with humility and ambition," Mr Kerry told an online meeting of the World Economic Forum on Wednesday.
"Humility, because we know we've wasted four years in which we were inexcusably absent.”
He said US President Joe Biden was putting climate change at the top of his agenda, promising the “most massive mobilisation of government around this issue in history".
But Mr Kerry said international efforts to curb global warming were falling short, calling temperature projections catastrophic.
“Even if we did everything that was promised in the Paris Agreement, the Earth’s temperature is going to rise," he said. "That’s where Paris left off."
Mr Kerry said he hoped talks in November at the UN climate conference in Glasgow, known as Cop26, would result in actionable steps.
"Glasgow, I believe is the last, best chance we have," the former US secretary of state told the panel.
“We have to go to Glasgow to hold ourselves accountable at a time when we know so much more about what it takes.”
Innovation from private enterprises would be crucial in helping the world to meet its climate objectives.
“I’m an optimist," Mr Kerry said. "I do believe we can get there but it will take a warlike enterprise, where B-24s are coming off the assembly line every hour. That’s how you have to approach this."
He was taking part in the Mobilising Action on Climate Change talk alongside Alok Sharma, president of the Cop26 Convention.
"We are in a fight for the very survival of our planet, for humanity, for nature, for biodiversity," Mr Sharma said. "It’s a matter of trust and countries have to deliver."
At the Accelerating Clean Energy Transitions discussion at Davos, Fatih Birol, executive director of the International Energy Agency, said there was no way the world could meet clean air targets without greatly increasing energy investments outside developed nations.
More than two thirds of emissions come from developing nations and that trend will continue in the coming decades, he said.
Focusing only on targets in the western world will not work because “emissions don’t have a passport”.
“If you want to avoid the effects of climate change in California, what happens in Jakarta or Delhi is extremely important,” he said.
"When you look at the clean energy investments in emerging countries, we need to multiply it almost by a factor of three.
"And when I look at the numbers, I don't see currently a big increase or big jump in the appetite of the investors."
EU Energy Commissioner Kadri Simson said that the coronavirus pandemic had not altered Europe’s commitment to clean air targets.
“We do understand the scale of the change needed," Ms Simson said. "Reducing greenhouse gases by 3 per cent to 5 per cent will need a lot on our side."
She said that 37 per cent of the EU recovery budget would go on the Green Deal, which invests in clean technology and businesses.
But Ms Simson made clear that Europe would be not be taking on the challenges alone, and that international co-operation would be “very important”.