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The head of the U.N.'s top science panel on climate change said Tuesday the world needs to "do more and faster" to prevent global warming on a scale that would cause irreversible environmental damage and hit poor societies hard.

Hoesung Lee, who chairs the Intergovernmental Panel on Climate Change, told diplomats at the U.N. climate summit in Poland that scientists had conducted an exhaustive review of data for their recent special report on keeping average global temperature increases to 1.5 degrees Celsius (2.7 Fahrenheit).

"The report shows that not just action, but urgent action is needed," Lee said.

His comments come as national leaders and ministers gathered in Katowice for the final stretch of the two-week talks, with just days left to break through thorny issues that diplomats have struggled to resolve.

U.N. climate chief Patricia Espinosa urged delegates to show a "spirit of unity" through the end of the week.

Lack of unity was on full display Saturday, when the United States, Russia, Saudi Arabia and Kuwait blocked endorsement of the IPCC's report . The move prompted anger from environmental groups, who accused the four countries of putting their interests as oil exporters before the need to curb global warming.

Scientists say emissions of greenhouses gases such as carbon dioxide — which is produced through burning of fossil fuels — need to drop significantly by 2030 and reach near-zero by the middle of the century if the 2015 Paris accord's most ambitious goal is to be achieved.

"We are moving in the right direction in many areas, but we need to do more and faster," said Lee, adding that cutting emissions sooner would give the world more room for maneuver later.

"Doing more now reduces reliance on unproven and risky techniques to remove carbon dioxide from the atmosphere," he said. "Doing less now would commit people today to the known risks of overshooting 1.5 C, with severe risks of irreversible loss of ecosystems and shocks to the basic needs of the most fragile human societies."

Lee warned that new coal-fired plants currently being built are an environmental and economic risk.

"Building coal and other fossil fuel power stations now commits governments to using that infrastructure for decades, running counter to our collective ambition," he said. "Or it risks wasting that investment by creating stranded assets."

Negotiators have until Friday to finalize the rules of the Paris accord, including details such as how countries will record and report their emissions.

The talks are also meant to push countries to commit to more ambitious targets for greenhouse gas emission reductions.

Poor countries, meanwhile, want assurances on financial support to tackle climate change.

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Read more stories on climate issues by The Associated Press at https://www.apnews.com/Climate