U.N. Secretary-General António Guterres urged countries Monday not to lose hope in the fight against climate change, as representatives from nearly 200 countries gathered in Madrid for a two-week meeting on tackling global warming.

»MORE: AJC poll shows Georgia voters want more done to fight climate change

In his opening speech to delegates, Guterres cited recent scientific data showing that levels of heat-trapping gases have hit a record high, reaching levels not seen for at least 3 million years when sea levels were 33 feet to 66 feet higher than today.

Unless emissions of carbon dioxide and other greenhouse gases are sharply cut, temperatures could rise to twice the threshold set in the 2015 Paris accord by the end of the century, he warned.

“Do we really want to be remembered as the generation that buried its head in the sand, that fiddled while the planet burned?” Guterres asked.

His appeal came after Chile’s environment minister, Carolina Schmidt, said the Dec. 2-13 meeting needs to lay the groundwork for moving toward carbon-neutral economies while being sensitive to the poorest and those most vulnerable to rising temperatures — something that policymakers have termed “just transition.”

»RELATED: How word use evolved in climate 'change' vs. 'crisis'

“Those who don't want to see it will be on the wrong side of history,” said Schmidt, who is chairing the meeting. She called on governments to make more ambitious pledges to reduce emissions of greenhouse gases ahead of a deadline to do so next year.

The summit, which moved to the Spanish capital after Chile had to pull out amid anti-government protests, aims to put the finishing touches to the rules governing the 2015 Paris accord.

That involves creating a functioning international emissions-trading system and compensating poor countries for losses they suffer from rising sea levels and other consequences of climate change.

“We have a common challenge but with differentiated needs and urgencies, which we can only overcome if we work together,” said Schmidt.

Countries agreed in Paris four years ago to limit global warming to well below 2 degrees Celsius , ideally 1.5C by the end of the century compared with pre-industrial times. Already, average temperatures have increased by about 1C, leaving little room for the more ambitious target to be met.

Guterres called out big greenhouse gas emitters that are still building coal-fired power plants, saying that unless the world stops burning coal "all our efforts to tackle climate change will be doomed."

He noted that had countries started cutting their emissions drastically a decade ago, reaching the Paris goal would have been much easier.

"The impact on all life on the planet — including ours — would be catastrophic. The only solution is rapid, ambitious, transformative action by all — governments, regions, cities, businesses and civil society, all working toward a common goal." — U.N. Secretary-General António Guterres

“Ten years ago, if countries had acted on the science, they would have needed to reduce emissions by 3.3% each year,” he said. “Today, we need to reduce emissions by 7.6% each year.”

“The impact on all life on the planet — including ours — would be catastrophic,” he added. “The only solution is rapid, ambitious, transformative action by all — governments, regions, cities, businesses and civil society, all working toward a common goal.”

»RELATED: Al Gore kicks off 24 hours of climate talks around world

Organizers expect about 29,000 visitors at the meeting, including about 50 heads of state and government for Monday’s opening session.

In contrast to the European Union, which sent its newly sworn-in executive leadership team to the summit, the rest of the world’s largest carbon emitters — the United States, China and India — have sent lower-level ministers and officials.

The U.S. sent a delegation, led by Ambassador Marcia Bernicat, a senior State Department official, even though President Donald Trump has formally begun the process of pulling the country out of the Paris accord. However, that won’t be technically completed until Nov. 4, 2020.

But Democratic members of Congress led by House Speaker Nancy Pelosi said the nation remains committed to the 2015 agreement’s goals and that climate change poses a threat to public health, the economy and national security.

House Speaker Nancy Pelosi  speaks during a news conference at the COP25 climate talks summit Monday in Madrid.

Credit: Andrea Comas

icon to expand image

Credit: Andrea Comas

“We’re still in it,” Pelosi said.

Asked about comments by Spain’s interim prime minister, Pedro Sánchez, that “only a handful of fanatics deny the evidence” of man-made global warming, Pelosi responded that she had “three words that describe how we address this: science, science and science. And maybe four: science, again.”

“If we can stick with the science, I think we can come up with some sane solutions to it all,” she said.

In an interview with The Associated Press, the U.N. chief hoped that stricter goals in Europe would allow EU leaders to convince fellow big polluters “to understand that this must be a collective effort and that they all will have to correct their policies in order to drastically be able to reduce the emissions.”