US President Joe Biden on Monday acknowledged that America and other developed nations bear much of the responsibility for climate change, and apologised for his predecessor Donald Trump's withdrawal from the Paris climate agreement.
The president said actions taken this decade to contain global warming will be decisive in preventing future generations from suffering.
“None of us can escape the worst that is yet to come if we fail to seize this moment,” Mr Biden declared.
He described the already visible crisis for the planet — flooding, volatile weather, droughts and wildfires — as a unique opportunity to reinvent the global economy.
Standing before world leaders gathered for the UN climate summit in Scotland, he sought to portray the enormous costs of limiting carbon emissions as a chance to create jobs by transitioning to renewable energy and electric automobiles.
The US leader went on to say sorry to the world for Mr Trump's withdrawal from the 2015 Paris climate deal.
“I shouldn’t apologise, but I do apologise for the fact the United States, the last administration, pulled out of the Paris Accords and put us sort of behind the eight ball a little bit," Mr Biden said.
The US is seeking to encourage other nations to make bold commitments on curbing the emissions blamed for Earth’s warming temperatures while his own domestic climate plan awaits a vote in the US Congress after a number of delays.
Speaking on Sunday ahead of the UN talks, Mr Biden also said fossil fuel use would remain necessary and he saw this as "not at all inconsistent" with climate goals as the world transitions to renewables.
“The idea we’re going to be able to move to renewable energy overnight and ... from this moment on not use oil or not use gas or not use hydrogen, it’s just not rational," Mr Biden said.
Speaking as he left the G20 summit in Rome on Sunday, Mr Biden said the US still needed petrol even as it aimed for electric vehicles to make up half of the traffic on US roads by 2030.
He also criticised China and Russia for their less-than-ambitious efforts to curb emissions.
On Monday, as Cop26 opened, UK Prime Minister Boris Johnson invoked James Bond and warned that delegates that younger generations would “not forgive us” if leaders did not seize the opportunity to deliver at the summit.
Mr Biden arrived at the Glasgow summit with his US envoy for climate, John Kerry, and was welcomed by former vice-president and environmental activist Al Gore.
Mr Biden will also attend some side events at the conference and a reception on Monday evening with other guests invited by the host, Mr Johnson.
The UN has warned countries that plans to cut climate-warming emissions in the next decade were not enough to put the world on track to limit warming to 1.5°C above pre-industrial levels.
Increasing temperatures above the 1.5°C target could lead to increasingly severe and extreme weather, rising seas levels and damage to crops, health and wildlife.
More than 120 leaders are set to attend the Cop26 summit, where countries are under pressure to deliver the financial support for poorer countries least responsible for, but most vulnerable to, climate change.
There will also be attempts to finalise parts of the Paris climate deal agreed to make it effective and operational.
Observers had hoped the meeting in Rome of leaders of the G20 nations, which between them emit nearly 80 per cent of global carbon output, would provide a strong impetus to Cop26, which was postponed for a year due to the pandemic.
Agencies contributed to this report