By ALESSANDRO TORELLO and SELINA WILLIAMS

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Su Wei, China’s chief negotiator on climate change, at the the second day of talks in Copenhagen.

COPENHAGEN — U.S. pledges to cut carbon-dioxide emissions 17% by 2020 aren’t ambitious enough, the Chinese lead negotiator at the climate-change talks said Tuesday, raising the pressure on rich nations to do more in reduction efforts and financial contribution to developing countries.

“We hope the U.S. will indeed bring a remarkable figure,” Su Wei told a news conference during the second day of talks. “This figure cannot be regarded as remarkable.”

The Chinese official also said that developed countries must provide money and technology for developing countries as they seek to limit their greenhouse-gas emissions and face the challenges of climate change. “They have the responsibility to provide financial support and technology transfer,” he said.

The U.K.’s Meteorological Office, meanwhile, said the current decade has been by far the warmest on record as it released new figures at the climate-change talks.

“Despite 1998 being the warmest individual year, the last 10 years have clearly been the warmest period in the 160-year record of global-surface temperature maintained jointly by the Met Office Hadley Centre and the Climatic Research Unit at the University of East Anglia,” the statement from the U.K.’s national weather service said.

The U.K. data are derived from a rolling average of 10 years in the 2000-09 period.

Independent analyses by the U.S. National Climatic Data Center and the National Aeronautics and Space Administration’s Goddard Institute for Space Studies show similar results, the statement said.

“These figures highlight that the world continues to see global temperature rise, most of which is due to increasing emissions of greenhouse gases into the atmosphere, and clearly shows that the argument that global warming has stopped is flawed,” the Met Office said.

The Met Office report comes despite recent temperature measurements showing average global temperatures were lower in 2006, 2007 and 2008 than in 2005. That measured dip in temperatures has sparked debate among scientists, even though 2006, 2007 and 2008 remain among the hottest on record.

Some scientists say the dip in temperatures from 2005, though slight, casts doubt on the premise that human activity is a main cause of climate change. Other scientists, in several recent papers, say the recent cooling is due to fleeting natural forces such as ocean currents that are likely to dissipate in the next several years, ushering a renewed period of global warming that they attribute largely to human activity.

But assessing the temperature increase over the decade 2000-2009 eclipses those annual details. Those who focus on examining temperatures over rolling ten-year periods say it is a more comprehensive way of showing temperature trends.

The U.K. measurements come from a global average temperature record made up of land-surface and sea-surface air temperatures. The Met Office compiles the data from sea measurements, and the Climatic Research Unit at the University of East Anglia compiles the data from land measurements.

However, though the rolling-10-year-average technique used for the study shows 2000-2009 as the warmest decade on record, the years since 2006, 2007 and 2008 each have been cooler than 2005, according to measurements from institutes including the University of East Anglia. The years 2006, 2007 and 2008 still are among the warmest on record. But they are cooler than 2005, according to these measurements.

The Met Office’s announcement follows controversy over leaked emails from the University of East Anglia’s Climatic Research Unit that have shaken climate science. Climate skeptics say the emails show that key data have been manipulated to strengthen the argument for climate change being man-made.

The Climatic Research Unit’s data are important as they were one of the global temperature records that have underpinned the Intergovernmental Panel on Climate Change’s assessment reports and numerous scientific studies.

However, a spokesman for the Met Office said the data used to show this decade was the warmest on instrumental record were reliable. “We’re 100% confident that the data are reliable and they are corroborated by two independent data sets in the U.S. which show similar warming,” Met Office spokesman Dave Britton said.

In a separate announcement, the World Meteorological Organization said that 2009 is likely to rank in the top 10 warmest years on record since the beginning of instrumental climate records in 1850.

Write to Alessandro Torello at alessandro.torello@dowjones.com and Selina Williams at selina.williams@dowjones.com