MADRID (AFP) -- Confronted with a climate crisis threatening civilization itself, humanity must choose between hope and surrender, UN chief Antonio Guterres told the opening plenary of a UN climate conference Monday.
"One is the path of surrender, where we have sleepwalked past the point of no return, jeopardizing the health and safety of everyone on this planet," Guterres said.
"Do we really want to be remembered as the generation that buried its head in the sand, that fiddled while the planet burned?"
In a separate forum moments earlier, U.S. Congressional leader Nancy Pelosi told the "COP25" conference that the world could still count on the United States despite President Donald Trump's decision to pull out of the Paris Agreement.
Leading the 15-strong Congressional delegation, Pelosi came to Madrid even as her colleagues in the House consider articles of impeachment against Trump.
Trump has dismissed global warming as a hoax, and dismantled many of the climate and environmental protection policies set in place by his predecessor Barack Obama.
Last month Trump gave formal notice of the U.S. withdrawal from the 196-nation Paris climate treaty, which calls for capping global warming at well below two degrees Celsius (3.6 degrees Fahrenheit), and 1.5C if possible.
In his impassioned appeal, Guterres cited new findings from the World Meterological Organization (WMO) confirming that the last five years have been the hottest ever recorded.
Concentration of planet-warming CO2 in the atmosphere has also reached levels not seen in three to five million years, the WMO will report this week.
"The last time there was a comparable concentration," Guterres said, "the temperature was two to three degrees Celsius warmer, and sea levels were 10 to 20 metres (32 to 66 feet) higher than today."
A major UN science report last year reset the Paris accord's threshold for a climate-safe world from 2C to 1.5C, concluding that the global economy must be "carbon neutral" by 2050 to stay under that threshold.
"What is still lacking is political will -- to put a price on carbon, to stop subsidies on fossil fuels, to stop building coal power plants," Guterres said.
"The best available science, through the Intergovernmental Panel on Climate Change (IPCC), tells us today that going beyond that (1.5C) would lead us to catastrophic disaster."