A metal sculpture sits in front of the Brandenburg Gate in Berlin Tuesday, Dec. 11, 2018 as Greenpeace activists protest against Germany's strategy against global warming. (Gregor Fischer/dpa via AP)

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.

The calls were echoed in speeches by the ministers as they took the floor on the first day of their plenary session. They urged all participants to show more ambition in setting national goals for the year 2020, and beyond. Coming from around the globe, they detailed the steps their governments and the financial contributions they are making to the cause of fighting climate change. They all stressed the urgency of the situation and the need for a joint approach.

Youth and indigenous groups protest against fossil fuels during US-hosted event at the UN climate talks in Katowice, Poland, Monday, Dec. 10, 2018, as the COP24 UN Climate Change Conference takes place in the city. (AP Photo/Frank Jordans)

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."

Participants in a U.N. climate conference walk by a screen showing high U.N. official for combatting climate change Patricia Espinoza, as she addresses the delegates in Katowice, Poland, Tuesday, Dec. 11, 2018. (AP Photo/Czarek Sokolowski)

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.

  • Delegates from Peru looking for a place to sit at the U.N. climate conference in Katowice, Poland, Tuesday, Dec. 11, 2018. (AP Photo/Czarek Sokolowski)

  • Participants in a U.N. climate conference sit on the floor during a break in their activities in Katowice, Poland, Tuesday, Dec. 11, 2018. (AP Photo/Czarek Sokolowski)