France, Dec. 12 -- Earth has warmed by about 0.46C since the deal was signed and the past decade has been the hottest on record. Scientists say governments have not moved fast enough to break dependence on coal, oil and gas, even though the accord has helped lower long-term temperature forecasts.

Johan Rockstrom, director of the Potsdam Institute for Climate Research, warned that the gap between action and impacts has grown as temperatures continue to rise and extreme weather intensifies.

"I think it's important that we're honest with the world and we declare failure," he said, adding that climate harms are arriving faster and more severely than expected.

Other voices point to progress the agreement has helped drive. Former UN climate ...