A 2007 report from the Intergovernmental Panel on Climate Change found "human influence" may have contributed to the climb in average global surface temperatures between 1951 and 2010, but the IPCC said increases have lessened since 1998, the BBC reported.
Arthur Petersen, lead scientist at the Netherlands Environmental Assessment Agency, told the BBC the trend would be a focal point of the IPCC agenda this week.
"Governments are demanding a clear explanation of what are the possible causes of this factor," he said in an interview published Monday.
Achim Steiner, executive director of the U.N. Environment Program, told delegates at an IPCC conference in South Korea in 2010 more work was needed to convince the public of the threats of global warming.
The BBC said climate-change skeptics may seize on the trends from 1998 by arguing that human influence is not as great as their rivals contend.