UN Secretary General Antonio Guterres opened two weeks of climate talks on Monday with a warning that countries could either increase their efforts to combat global warming or blindly stumble toward a disaster that imperils civilisation.
The COP25 conference in Madrid is the latest attempt to persuade world leaders to act on the peril of rising temperatures. It comes a month after the US formally announced that it would exit the Paris Climate Accord, struck in 2015.
That withdrawal – the agreement called for capping of global warming at well below 2°C, and 1.5°C if possible – hangs heavy over international efforts to address climate change.
The schism was increasingly evident by the attendance in Madrid of US House speaker Nancy Pelosi, who said Democrats would rejoin the Paris deal if they win back the White House from Donald Trump's Republicans in November next year.
Mr Guterres, however, centred his speech on a familiar refrain about the impact on future generations it there is a failure to act and how nations faced a stark choice.
“One is the path of surrender, where we have sleepwalked past the point of no return, jeopardising the health and safety of everyone on this planet,” he said.
“Do we really want to be remembered as the generation that buried its head in the sand, that fiddled while the planet burned?
“The other option is the path of hope ... where more fossil fuels remain where they should be – in the ground – and where we are on the way to carbon neutrality by 2050.”
Despite the intended US pullout from the Paris agreement, a State Department delegation is attending the Madrid talks “to ensure a level playing field that protects US interests”, according to a statement released on Saturday.
The disjointed stance of American politicians on climate, however, was laid bare by the appearance of Ms Pelosi at the head of a 15-member US congressional delegation. Her Democratic Party is pursuing the possible impeachment of President Trump.
“We're here to say to all of you, on behalf of the House of Representatives and the Congress of the United States, we're still in it, we're still in it,” Ms Pelosi said to applause at a forum of heads of state from climate-vulnerable nations.
“We see this as an existential threat. We have not lived up to the challenge.”
Mr Trump has dismissed global warming as a hoax, dismantling many of the climate and environmental protection policies set in place by his predecessor, Barack Obama.
US Secretary of State Mike Pompeo gave formal notice of the US withdrawal from the 196-nation Paris climate treaty on November 4, further isolating America from much of the rest of the world on climate issues after the Trump administration's backing of coal producers.
The 12-day meeting in Madrid is aimed at finalising the rules and procedures for the Paris deal, which becomes operational at the end of next year.
Virtually all Democratic candidates for the US presidency have made global warming a major issue in their campaigns. Some have called for ambitious economic aid programmes to address global warming, stressing that a failure to do so will damage not only human existence but also the American and wider global economy.
Nearly two-thirds of the US population and gross domestic product is under states or sub-national regions committed to adhere to the Paris temperature goals, according to "We Are Still In", a coalition of local governments, businesses and citizen groups.
“There is no doubt that a second Trump term of office would be a challenge not just to Paris, but to a whole range of multilateral agreements,” said Alden Meyer, director of strategy and policy for the Union of Concerned Scientists, a US non-profit founded in 1969 by scientists and students at the Massachusetts Institute of Technology.